Chemistry: A Volatile History
Encyclopedia
Chemistry: A Volatile History is a 2010 BBC
documentary on the history of chemistry
presented by Jim Al-Khalili
. It was nominated for the 2010 British Academy Television Awards
in the category Specialist Factual.
is – a substance that cannot be broken down further by chemical reaction
.
The Ancient Greeks, with no way of breaking open substances, could only base their ideas of the elements on what they could see: Earth, Fire, Water and Air.
In the 16th century alchemists were busy trying to turn base metals like lead, into gold.
who first challenged the Ancient Greek idea of four elements.
In 1526 Paracelsus was in Basel, when the famous printer Frobenius
was told he would have to have his leg amputated in a life-saving operation. Instead of accepting the received wisdom, he called upon Paracelsus who cured him in the unconventional way of using his alchemical knowledge. This established him as a radical thinker, giving weight to his ideas, principal amongst which was the idea that the world was actually made of three elements: the tria prima comprising salt, sulphur and mercury.
Paracelsus did not succeed in convincing the establishment – instead he managed to enrage them by burning their established medical texts, and eventually had to flee Switzerland for Germany.
It was, however, the alchemical pursuit for gold that lead to the first breakthrough in the hunt for new elements.
was looking for a way of extracting gold
from the human body, and struck upon the idea of using urine, thinking that urine might contain some part of the ‘life force’ vital to sustaining human life. To get rid of the unimportant parts, primarily water, Brand boiled the urine for several days until he was left with a thick paste. Finally, fragments of a substance emerged which burned brighter than any Medieval candle available at the time, but which left the vessel it burnt in cold: Brant named this new substance icy noctiluca – ‘cold night light’.
Soon after its discovery, icy noctiluca toured the Royal Houses of Europe and in 1677 it came before the Royal Society
in London, then under the chairmanship of Charles II
, where one of its members decided to investigate.
In his book New Experiments and Observations Made Upon the Icy Noctiluca Robert Boyle
describes an experiment in which sulphur and phosphorus powders are mixed causing them to burn fiercely. This discovery was the basis for the invention of the match.
Phosphorus
, as icy noctiluca is now known, is used in everything from match heads to toothpaste and ultimately in the Second World War bombs which destroyed the very city in which Brand discovered it – Hamburg.
Whilst Brand never discovered gold, his accidental discovery of the element now known as phosphorus gave rise to the idea that elements could be hidden inside other substances.
Boyle was willing to share his discoveries to allow others to build on his work and further the scientific understanding of the elements. He wanted to put alchemy on a more scientific footing – ditching the metaphysical baggage it had brought with it from the previous century.
Unfortunately, this new age of chemical enlightenment was fraught with blind alleys.
proposed that fire was caused by an ethereal, odourless, tasteless, colourless, weightless entity called phlogiston. The idea was that phlogiston causes things to burn, reducing them to their pure form. For example, burning wood releases phlogiston, leaving the pure form of wood – ash, therefore wood is composed of ash (pure wood) and phlogiston.
Phlogiston was accepted as scientific truth, paralysing the scientific community’s ability to discover more, true elements. One scientist even claimed to have isolated phlogiston.
with royal connections, Henry Cavendish
was a painfully shy character, who made the vital chemical contribution of discovering the first elemental gas.
He added some zinc to spirit of salt (hydrochloric acid
) and collected the evanescence given off as bubbles. The gas he collected was tasteless, odourless and colourless, and moreover it produced a squeaky pop in the presence of a flame – this lead Cavendish to name the gas inflammable air, which he believed to be one and the same as phlogiston.
Cavendish made an important observation, though little did he realise it, about burning phlogiston in air, a dewy liquid was formed on the inside of the glassware: water
. This should have had enormous repercussions for the whole scientific community in the 1700s, who still believed water to be an elemental substance. Yet, if water could be made by burning inflammable air, then water is not an element, but a compound
.
However, it simply did not occur to Cavendish that water was a compound – instead he assumed that the airs contained a form of water, which phlogiston modified into liquid, elemental water.
Phlogiston had given the Ancient Greek idea of water as an element a brief reprieve, but the Greek system was now under heavy scrutiny as the Royal Society commissioned its members to investigate the invisible airs.
It was this last air which caught the attention of Joseph Priestly, a Unitarian minister whose favourite pastime was the investigation of airs – specifically, fixed air, given off by the fermentation process in breweries.
Priestly’s passion for science lead to an invitation to Bowood House
, to tutor the children of Lord Shelburne. This was an excellent opportunity, given that Priestly did not have the money of earlier chemists like Boyle and Cavendish, and would still be free to pursue his own research.
In 1774 Priestly performed a hugely important experiment: he heated mercuric calc and collected the gas given off. He discovered that this gas was able to relight the embers of a previously lit wooden splint. He concluded that the splint was introducing phlogiston to the gas, only after which could it burn, therefore the gas must be ‘without phlogiston’ – this lead Priestly to name it dephlogisticated air.
In October 1775 Priestly accompanied Lord Shelburne on a trip to Paris where they were invited to dine with the preeminent scientists of the time. It is here that Priestly met the French scientist Antoine Lavoisier
.
Lavoisier weighted a sample of tin, then reweighed after he had heated it and found it had increased in mass. This was an unexpected result given that the tin was thought to have released phlogiston during the burning process. Lavoisier was struck with a ground-breaking thought – maybe the tin had absorbed something from the air, making it heavier, but if so, what?
To investigate this further, Lavoisier reran Priestly’s experiment in reverse – he heated some mercury in a sealed container until it turned into mercuric calc and measured the amount of air absorbed. He then heated the mercuric calc and measured the amount of air released and discovered the quantities were the same. Lavoisier realised that something was absorbed from the air when mercury was heated to make mercuric calc, and that same gas was released when the mercuric calc was heated. Lavoisier concluded that this gas was unrelated to phlogiston, but was in fact a brand new element, which he named oxygen
.
Lavoisier had successfully dispensed with the need for the theory of phlogiston and recognised Priestly’s ‘dephlogisticated air’ as the element oxygen. Despite the fact it was Priestly’s original work that laid the foundations for his discovery, Lavoisier claimed he had discovered oxygen; Priestly, after all, had failed to recognise it as a new element.
Lavoisier went on to give science its first definition of an element: a substance that cannot be decomposed by existing chemical means. He also set about drawing up a list of all the elements – now 33 elements replaced the ancient four. His list was grouped into four categories: gases, non-metals, metals and earths.
On top of this, Lavoisier created a classification system for the ever increasing array of chemicals being discovered. As mentioned, ‘dephlogisticated air’ became oxygen, ‘inflammable air’ became hydrogen
, but the nomenclature of compounds was also put on a more logical footing as ‘oil of vitriol’ became sulphuric acid, ‘philosophical wool’ became zinc oxide and ‘astringent mars saffron’ became iron oxide.
Unfortunately, whilst Lavoisier had rid the world of the phlogiston paradigm, he introduced two new erroneous elements now known to be pure energy: lumière and calorique; light and heat.
In revenge for his sympathies with the revolutionaries in France, Priestly’s home in England was targeted by arsonists in 1791, luckily he escaped thanks to a tip-off, but decided to flee to America. Lavoisier’s contributions to science were cut short in 1794 by the revolutionaries, who arrested him on grounds of being an enemy of the French people, and had him guillotined.
because he was unconvinced potash was an element, but by the end of the previous century, Lavoisier had been unable to break it down further.
Since then however, the first electric battery
had recently been invented (rows of metal plates and cardboard soaked in saltwater). Although scientists were aware that the production of a continuous electric current was due to some property of the metals, Davy believed that a chemical reaction was taking place. If that was true, then maybe the reverse was also true: an electric current could cause a chemical reaction.
Davy heated the potash until it was liquid, then introduced two electrodes and passed a current through the molten potash. A lilac flame was observed, the result of successfully breaking down potash into its constituent elements – one of which, was the previously never before seen element potassium
.
Davy went on to add six new elements to Lavoisier’s list, as well as confirming that substances like chlorine
and iodine
were also elements. By the time of his death in 1829 the idea of the elements was firmly established, 55 separate elements had been discovered, and the world had a new science: Chemistry.
thought that for this to happen, each element had to be made of its own unique building blocks, which he called atoms
.
Dalton suggested that everything in the universe was made of atoms, and that there are as many kinds of atoms as there are elements, each one with its own signature weight. Based on these ideas, working completely alone, Dalton attempted to impose some order on the elements by drawing up a list, where each element was represented by an alchemical-looking symbol, ordered by atomic weight
.
Although Dalton did not get all his atomic weights correct, he was pointing science in the right direction. Sadly, in the early 1800s few scientists accepted the idea that elements had different weights.
was one of the few scientists who strongly believed in the idea of atomic weights, and thought that knowing as much as possible about their weights was vitally important. When he heard of Dalton’s theory, he set about the gargantuan task of measuring the atomic weight of every single known element – without any proof that Dalton’s atoms actually existed.
This was even more challenging than it first seems once you consider the fact that very little of the chemical glassware necessary for such precise measurements had been invented. Berzelius had to manufacture much of it himself.
Berzelius’ experiences with glass-blowing had an additional bonus, in 1824 he discovered that one of the constituents of glass was a new element – silicon
. Having already discovered three other elements prior to silicon: thorium
, cerium
and selenium
, Berzelius spent the next ten years obsessively measuring more than two thousand chemical compounds in pursuit of accurate atomic weights for the elements. Eventually Berzelius had remarkably accurate atomic weights for 45 elements; his value for chlorine was accurate to within 0.2% of the value we know today.
However, by the time Berzelius had produced his results, other scientists were now measuring atomic weights – and getting conflicting results. In fact, scientists were looking for all sorts of patterns throughout the elements.
The problem was that Döbereiner’s triads only worked for a few of the elements and got scientists no further than atomic weights.
to St Petersburg – walking a significant portion of the route – so her son Dmitri Mendeleev
could continue his education in the capital of the Russian Empire
.
At the time the scientific community was grappling with the problem of how to bring order to the 63 elements that were now known. Mendeleev was still a student when he attended the world’s first international chemistry conference – convened to settle the confusion surrounding atomic weights.
chemist Stanislao Cannizzaro
was still convinced that atomic weights held the key to the order of the elements and had found a new way of measuring them. Cannizzaro knew that equal volumes of gases contain equal numbers of particles, therefore instead of working with solids and liquids and all the unreliability that entails, he proposed measuring the densities of gases to measure the weights of individual gaseous atoms.
Whereas Berzelius’ results had failed to convince anyone, Cannizzaro’s method set an agreed standard for measuring atomic weights accurately. Chemists soon found that even with accurate atomic weights, the elements still seemed unordered, but then, a solitary English chemist made a curious discovery.
noticed that when ordered by weight, every eighth element seemed to share similar properties, such as carbon and silicon in the sequence: carbon, nitrogen, oxygen, fluorine, sodium, magnesium and silicon. He called this a Law of Octaves.
Three years later, in 1866, he presented his ideas to the Chemical Society
, unfortunately for Newlands, the musical analogy was not well received – the audience suggesting he might as well have ordered the elements alphabetically.
Today, Newland’s Octaves are known as the Law of Periodicity, and Mendeleev was thinking along the same lines.
To date, chemist had tried to group elements in one of two ways:
Mendeleev’s genius was to combine those two methods together. However, the odds were stacked against him – little more than half the known element had been discovered: he was playing with an incomplete deck of cards.
He stayed up for three days and nights then, finally, on 17 February 1869, he fell asleep and dreamt of all 63 known elements laid out in a grand table
.
Mendeleev’s table reveals the relationship between all the elements in their order:
Notice carbon and silicon are in Group IV and the volatile gases fluorine, chlorine and bromine are in Group VII.
Mendeleev was sufficiently confident in the layout of his table that he was willing to leave gaps for unknown elements to make the pattern fit – believing other elements would later be discovered that filled the gaps.
So, for Mendeleev to be vindicated, the gaps needed to be filled, and luckily, in 1859, new instrumentation had been developed for discovering elements.
knew that when certain elements burned in the flames of his burner they each turned the flame a different colour. Copper burned green, strontium red and potassium lilac – Bunsen wondered if every element had a unique colour.
Bunsen was joined in his research by Gustav Kirchhoff
. Kirchhoff used the concept of the dispersion of white light by a prism in the invention of the spectroscope, a device with a prism at its centre which split the light from Bunsen’s flames into distinct bands of its constituent colours – the element’s spectral lines.
Kirchhoff and Bunsen realised these spectral lines were unique to each element, and, using this technique they discovered two new elements, caesium and rubidium.
used a spectroscope to discover a new metallic element. It was a silvery-white, soft metal with an atomic weight of 68, which he named gallium
, after his native France. It also turned out to have a very low melting point, thus matching all the expected properties of the element Mendeleev expected to fill the gap he had left after zinc; indeed, this is exactly where the element was placed in the periodic table.
Even though Mendeleev had left the necessary gap for gallium as well as other elements, it was becoming clear there was an entire group that was missing altogether.
that occurred in August of that year. As well as his telescope, he also went equipped with a spectroscope, to study the spectral lines of the light emitted from the sun. Normally, due to the intensity of sunlight many weaker spectral lines are not visible next to the extreme brightness of the stronger lines. Janssen hoped that he would observe more spectral lines during the eclipse when the sun’s light was less intense.
The eclipse allowed Janssen to observe a spectral line never seen before, which was not associated with any known element. The same spectral line was confirmed by the English astronomer Norman Lockyer, who thinking the element only existed in the sun, named it helium
, after the Greek Sun God.
However, it wasn’t long before another British scientist had discovered helium on Earth.
was able to collect a gas trapped within the rock, which had an atomic weight of 4, and the same spectral lines which Lockyer had observed: helium. Prior to this, Ramsay had already isolated a new gas from the atmosphere; argon
, with an atomic weight of 40.
A problem now arose – Mendeleev had not left any gaps which were suitable for either of these two new elements, which lead Ramsay to conclude an entire group was missing from the periodic table – only two of whose members were now known to exist, helium and argon.
Ramsey successfully discovered all the other stable elements in the group which he named neon
(Greek for new), krypton
(Greek for hidden) and xenon
(Greek for stranger). All the elements of this new group had one overwhelming characteristic; their lack of reactivity. It was this particular characteristic that brought to mind a name for the new group: the noble gases.
.
The periodic table does not however tell us why some elements are highly reactive, others completely inert, why some are volatile, whilst others less so. It wasn’t until the beginning of the 20th century that an entirely different branch of science began to unravel the answers to these questions.
proposed the structure of the atom was like that of a solar system: mostly empty space with electrons floating around a dense nucleus.
Subsequently the Danish Physicist Niels Bohr
introduced the idea that electrons occupied “fixed shells” around the nucleus, which was further developed when it was suggested that each such shell could only accommodate a fixed number of electrons: 2 in the first shell; 8 in the second shell; 18 in the third shell, and so on, each shell holding an increasing number of electrons.
The chemical behaviour of all elements is explained by the number of electrons in their outer shells: to increase the energetic stability of their electron configurations atoms have a tendency to gain or lose electrons in such a way so as to achieve a full outer shell. Sodium, with 11 electrons – one in its outer-most occupied shell, will transfer an electron in the presence of fluorine to its outer-most occupied shell, which contains seven electrons. The result is both sodium and fluorine now have a full outer shell, and Sodium Fluoride is formed.
This theory explained why all elements react in the way they do and why some formed the compounds they do, while others did not. It also explained why elements had the physical properties they did, which in turn explained why the periodic table had the shape it did. However, there was one fundamental question left unanswered: how many elements were there – could there be an infinite number of elements between Hydrogen and Uranium?
speculated that the answer to the number of elements lay in the nucleus. By firing a radioactive source at copper, he was able to knock electrons from their atoms, releasing a burst of energy in the form of an x-ray
. When measured, the x-rays always had the same energy, unique to copper. He discovered each element released x-rays of different energies. Moseley’s brilliance was to realise the x-ray energy is related to the number of protons inside the atom: the atomic number
.
Because this is the number of protons, the atomic number must be a whole number – there cannot be any fractional values. Mosley realised it was the atomic number, not the atomic weight that determines the order of the elements. What’s more, because the atomic number increases in whole numbers from one element to the next there can be no extra elements between Hydrogen (atomic number 1) and Uranium (atomic number 92) – there can only be 92 elements, there is no room for any more.
Moseley was just 26 when he completed this research. Aged 27 he was killed in action during the First World War – shot through the head by a sniper.
. Glass is made of silicon and oxygen.
Since prehistoric times, people have been engaging in ‘bucket chemistry’ – adding all sorts of chemicals together, just to see what would happen. As a result, many early discoveries in chemistry were accidental.
, Heinrich Diesbach
was trying to produce a synthetic red paint. He started by heating potash (potassium carbonate), with no idea that his potash had been contaminated with blood. When heated, the proteins in blood are altered, allowing them to combine with the iron in the blood, whilst the carbonate reacts with the haemoglobin to produce a solid.
After heating the resulting solid to an ash, filtering and diluting, Diesbach added green vitriol (iron sulphate) to create a complex ion: ferric ferrocyanide. Finally, adding sprit of salt (hydrochloric acid) draws out a brilliant colour: Prussian Blue
.
, had become obsessed with trying to better understand the elements by creating explosive combinations. Specifically, he was interested in the explosive compound silver fulminate.
In 1825 he read a paper written by Friedrich Wöhler
in which he describes a compound called silver cyanate, made in equal parts of silver, carbon, nitrogen and oxygen, which he described as harmless and stable. von Liebig immediately wrote back a furious letter condemning Wöhler as a hopeless analyst: those elements combined in equal proportions were exactly what made the explosive silver fulminate.
Instead of backing down, Wöhler challenged von Liebig to make silver cyanate for himself. The results would have astounded him – the same elements that combined according to von Liebig’s method, when combined according to Wöhler’s method made two completely different compounds.
Wöhler and von Liebig had inadvertently discovered isomerism: the same number of atoms of the same elements combining in different ways to make different compounds. In time, this would explain how just 92 elements could make the vast array of compounds we know today.
Chemists started to realise that understanding the arrangement of atoms within compounds was crucial if they wished to design new compounds, and the first step in this direction was taken by studying carbon.
was experimenting on diamonds when he decided to burn one. Using only sunlight and a magnifying glass he managed to ignite a diamond sufficiently for it to produce a gas, which he collected and was able to identify as carbon dioxide.
Having started with only diamond and oxygen, and produced a gas which contains only carbon and oxygen, Tennant had discovered that diamonds are made of carbon.
Unaware of atomic theory at the time, scientists were unable to explain how carbon, already known to exist as one of the softest substances in the form of graphite
, could also be the sole constituent element of the hardest known substance: diamond
.
Exactly 50 years later, a young Scottish chemist discovered there are no prizes in Science for coming second.
went to work for a French chemist, Charles-Adolphe Wurtz
. Whilst in Paris he came up with the idea of links between atoms that could explain how individual atoms formed compounds. He called these links bonds. Somehow, Couper realised that carbon can form four bonds, thereby attaching itself with different strengths to other carbon atoms in a compound:
The ability of carbon to form four bonds also means it can exist in a huge variety of chemical structures, such as long chains and even rings, making it a rarity amongst the elements. This helped to explain the abundance of carbon in all life forms, from protein and fat, to DNA and cellulose, and why carbon exists in more compounds than any other element.
All that remained for Couper was to get his paper published...
Meanwhile in Paris, Wurtz had been slow to publish Couper’s paper and Kekulé, whose work appeared in print first, claimed all the credit. When Couper discovered Wurtz had delayed in sending his paper to be published he flew into a rage and was promptly expelled from the laboratory by Wurtz.
The crushing disappointment at having lost out on his chance of scientific recognition led him first to withdraw from Science and then to suffer a nervous breakdown. He spent years in and out of an asylum.
However, now that scientists were beginning to understand the way carbon combines with itself and other elements, it was possible to create new compounds by design and industrial chemistry was born.
successfully drew off a fibre from the interface of two liquids: hexane-1,6-diamine and decanedioyl-dichloride, which could be spun into a very fine, very strong thread. It was given the name nylon
.
Shockingly, only three weeks after the patent for nylon had been filed, a depressed Carothers slipped another carbon based compound into his own drink, potassium cyanide, and killed himself.
Evidently, industrial chemistry wasn’t without its downsides, and one chemist was arguably responsible for single-handedly polluting the entire Earth with lead
.
, Thomas Midgley
experimented with a myriad of different compounds, which he added to petrol in an attempt to prevent engines from knocking. Eventually, he discovered one compound that worked brilliantly: tetra-ethyl lead
.
By the 1970s the use of leaded petrol was ubiquitous worldwide, but research was emerging about the damage that it was doing to humans and the environment. In 1983, a Royal Commission
asked the question: “Is there any part of the Earth’s surface, or any form of life that remains uncontaminated?”
Today nearly all petrol is unleaded, although lead lives on in motor vehicles in their batteries.
was working with uranium
crystals when he found UV light made them glow. Leaving the uranium crystals on an unexposed photographic plate overnight, he returned the next morning to discover they had caused the part of the plate they were sat on to develop.
Becquerel correctly reasoned the only source of energy that could have caused this was the crystals themselves. He had discovered radioactivity, and a young Polish scientist began to investigate.
began her investigations by testing a uranium ore called pitchblende with an electrometer. She discovered it was four times more radioactive than pure uranium, and wondered if this was due to the presence of an even more radioactive element in the pitchblende.
Curie began stockpiling tonnes of pitchblende, then in the most basic of workshops with primitive equipment she undertook a multitude of complex and dangerous procedures in an attempt to isolate this new element.
In the event, Curie discovered two new elements, polonium
named after her native Poland and radium
. Whilst these were naturally occurring elements, they fuelled a scientific desire to create entirely new, artificial elements.
had already revealed the structure of an atom to consist mostly of empty space with a dense nucleus of protons at the centre, and Henry Mosley had shown that it is the number of protons that gives an atom its identity as a particular element. An atom of the element carbon has 6 protons, whilst an atom with 7 protons is one of nitrogen.
Rutherford came to the conclusion that the number of protons in a radioactive element could change – through a process of decay where parts of the nucleus are ejected from the atom. Rutherford named these fragments of ejected nucleus alpha particles.
Rutherford realised that if an atom is losing protons, its identity is changing at the same time, since an atom’s identity is governed by its proton number. Radioactive decay causes atoms of one element to transmute into atoms of a different element. He then sought to artificially engineer a specific transmutation.
Rutherford fixed a source of alpha particles – each of which contains two protons – at one end of a cylindrical chamber. At the other end he fixed a screen. Each time an alpha particle reached the screen it produced a flash. He then introduced nitrogen into the chamber and observed additional, different flashes on the screen. Occasionally, an alpha particle would collide with a nitrogen nucleus and get absorbed by it, knocking out a proton in the process. These protons then travelled on through the chamber to the screen to produce the additional flashes.
However, the nucleus of nitrogen – having absorbed two protons but lost only one – had gained a proton and become a nucleus of oxygen. Rutherford’s work gave hope to scientists trying to create new elements, but one final discovery about the atom was necessary.
In 1932 the Cambridge scientist James Chadwick
discovered the neutron – electrically neutral particles which also sit inside the nucleus along with the protons.
– nicknamed ‘the pope’ by his colleagues for his infallibility, realised the potential of the newly discovered neutron in the search for elements heavier than uranium. Until now, scientists had been bombarding uranium with alpha particles in the hope they would enter the nucleus. Unfortunately, this was very unlikely because both alpha particles and nuclei are positively charged – the alpha particles could never overcome the electrostatic repulsion of the nucleus.
Fermi reasoned that because neutrons carried no electric charge, they would have a much better chance of penetrating the nucleus of a uranium atom. So Fermi set about firing neutrons at uranium. Fermi thought that this, coupled with his knowledge of beta decay
, whereby an unstable nucleus attempts stabilisation by converting one neutron to a proton and ejecting a newly formed electron, would result in an element with one extra proton than uranium: element 93.
Indeed, Fermi discovered elements he did not recognise. He tested for elements below uranium in the periodic table: radon, actinium, polonium, as far back as lead – it was none of these. So, in 1934, the infallible Fermi declared to the world he had created elements heavier than uranium.
, decided to investigate Fermi’s bold claim. Unfortunately for Fermi, they quickly disproved his assertion; one of the elements produced was barium
, which, with 56 protons, was nowhere near the 92 protons the nucleus started with when it was uranium.
Hahn wrote of his confusion to his colleague Lisa Meitner who, as an Austrian Jew, had recently fled Nazi Germany for Sweden.
.
However, in doing the calculations for such an event, Meitner was unable to make the equations balance. She calculated that the products of the fission reaction were lighter than the initial uranium, by about one fifth of a proton. Somehow, a small amount of mass had disappeared. Then slowly, the solution to this discrepancy occurred to Meitner – Einstein and E = mc2
– the missing mass had been converted to energy.
aimed at creating the first atomic bomb.
For an explosion to occur, there must be a rapid release of energy – a slow release of energy from uranium nuclei would give a uranium fire, but no explosion. Both sides poured their effort into creating the necessary conditions for a chain reaction
.
In 1942 Enrico Fermi, now living in America, successfully induced a chain reaction in uranium, but processing uranium for bombs was both difficult and costly. America had just come up with a different solution to win the atomic race.
Now finally, scientists’ dream of creating an element beyond the end of the periodic table was about to be realised.
Edwin McMillian and Phillip Ableson blasted uranium with a beam of particles to create the first synthetic element, heavier than uranium – element 93, which they named neptunium
.
The next synthetic element, plutonium
, quickly followed in 1941, which scientists realised was readily able to undergo fission in a way capable of producing the desired chain reaction. It was soon being made into a bomb.
A mere seven years after the discovery of nuclear fission, on 6th August 1945, half a gram of uranium was converted into energy when the world’s first atomic bomb was dropped on Hiroshima
. As Lisa Meitner’s calculations suggested, this conversion released energy equivalent to 13,000 tonnes of TNT. A plutonium bomb was dropped on Nagasaki
three days later.
These physicists have become the new chemists – testing the foundations of the periodic table, and hence our understanding of the universe, in light of new discoveries.
In addition to producing new elements, scientists are also attempting to discern their properties. Copernicium is found to be a volatile metal that would be liquid at room temperature if enough were ever made – exactly what Mendeleev would predict for element 112 – which sits directly beneath mercury in the periodic table.
BBC
The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...
documentary on the history of chemistry
History of chemistry
By 1000 BC, ancient civilizations used technologies that would eventually form the basis of the various branches of chemistry. Examples include extracting metals from ores, making pottery and glazes, fermenting beer and wine, making pigments for cosmetics and painting, extracting chemicals from...
presented by Jim Al-Khalili
Jim Al-Khalili
Jim Al-Khalili OBE is an Iraqi-born British theoretical physicist, author and science communicator. He is Professor of Theoretical Physics and Chair in the Public Engagement in Science at the University of Surrey...
. It was nominated for the 2010 British Academy Television Awards
British Academy Television Awards 2010
The 2010 British Academy Television Awards were held on 6 June 2010. The nominations were announced on 10 May.This year new awards were added including the award for Best Actor/Actress in a Supporting Role. Graham Norton hosted the ceremony...
in the category Specialist Factual.
Introduction
Only in the last 200 years have we known what an elementElement
- Chemistry, electronics, or the geosciences :* Chemical element, a building block in chemistry* Electrical element, an abstract part of a circuit* Heating element, a device that generates heat by electrical resistance...
is – a substance that cannot be broken down further by chemical reaction
Chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...
.
The Ancient Greeks, with no way of breaking open substances, could only base their ideas of the elements on what they could see: Earth, Fire, Water and Air.
In the 16th century alchemists were busy trying to turn base metals like lead, into gold.
Paracelsus and the Tri Prima
It was the Swiss alchemist and surgeon ParacelsusParacelsus
Paracelsus was a German-Swiss Renaissance physician, botanist, alchemist, astrologer, and general occultist....
who first challenged the Ancient Greek idea of four elements.
In 1526 Paracelsus was in Basel, when the famous printer Frobenius
Johann Froben
Johann Froben, in Latin: Johannes Frobenius , was a famous printer and publisher in Basel...
was told he would have to have his leg amputated in a life-saving operation. Instead of accepting the received wisdom, he called upon Paracelsus who cured him in the unconventional way of using his alchemical knowledge. This established him as a radical thinker, giving weight to his ideas, principal amongst which was the idea that the world was actually made of three elements: the tria prima comprising salt, sulphur and mercury.
Paracelsus did not succeed in convincing the establishment – instead he managed to enrage them by burning their established medical texts, and eventually had to flee Switzerland for Germany.
It was, however, the alchemical pursuit for gold that lead to the first breakthrough in the hunt for new elements.
Hennig Brand and the Icy Noctiluca
In 1669 BrandHennig Brand
Hennig Brand was a merchant and alchemist in Hamburg, Germany. He discovered phosphorus around 1669.-Early life:The circumstances of Brand's birth are unknown. Some sources describe his origins as humble and indicate that he had been an apprentice glass-maker as a young man...
was looking for a way of extracting gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
from the human body, and struck upon the idea of using urine, thinking that urine might contain some part of the ‘life force’ vital to sustaining human life. To get rid of the unimportant parts, primarily water, Brand boiled the urine for several days until he was left with a thick paste. Finally, fragments of a substance emerged which burned brighter than any Medieval candle available at the time, but which left the vessel it burnt in cold: Brant named this new substance icy noctiluca – ‘cold night light’.
Soon after its discovery, icy noctiluca toured the Royal Houses of Europe and in 1677 it came before the Royal Society
Royal Society
The Royal Society of London for Improving Natural Knowledge, known simply as the Royal Society, is a learned society for science, and is possibly the oldest such society in existence. Founded in November 1660, it was granted a Royal Charter by King Charles II as the "Royal Society of London"...
in London, then under the chairmanship of Charles II
Charles II of England
Charles II was monarch of the three kingdoms of England, Scotland, and Ireland.Charles II's father, King Charles I, was executed at Whitehall on 30 January 1649, at the climax of the English Civil War...
, where one of its members decided to investigate.
In his book New Experiments and Observations Made Upon the Icy Noctiluca Robert Boyle
Robert Boyle
Robert Boyle FRS was a 17th century natural philosopher, chemist, physicist, and inventor, also noted for his writings in theology. He has been variously described as English, Irish, or Anglo-Irish, his father having come to Ireland from England during the time of the English plantations of...
describes an experiment in which sulphur and phosphorus powders are mixed causing them to burn fiercely. This discovery was the basis for the invention of the match.
Phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
, as icy noctiluca is now known, is used in everything from match heads to toothpaste and ultimately in the Second World War bombs which destroyed the very city in which Brand discovered it – Hamburg.
Whilst Brand never discovered gold, his accidental discovery of the element now known as phosphorus gave rise to the idea that elements could be hidden inside other substances.
Robert Boyle and The Sceptical Chemist
More than a decade earlier in 1661, a year after the Royal Society opened, Boyle deposited The Sceptical Chemist in its vaults. This book is usually regarded as the turning point that signalled the transition from alchemy to chemistry. The Sceptical Chemist was innovative in several ways: it was not written in Latin, as had been the tradition for alchemical books, but in English; it dispensed with the old alchemical symbols for various elements, using English names instead; and most crucially it was actually published, as opposed to kept secret.Boyle was willing to share his discoveries to allow others to build on his work and further the scientific understanding of the elements. He wanted to put alchemy on a more scientific footing – ditching the metaphysical baggage it had brought with it from the previous century.
Unfortunately, this new age of chemical enlightenment was fraught with blind alleys.
Johann Becher and Phlogiston
In 1667 the German scientist Johann BeckerJohann Becker
Johann Becker was a German organist, teacher, and composer, born in Helsa-Wickenrode, near Kassel. He studied with Bach in Leipzig from about 1745 to 1748. He taught in Hartmuthsachsen, Bettenhausen, and Kassel, where in 1761 he was appointed municipal organist. In 1770 he was appointed court...
proposed that fire was caused by an ethereal, odourless, tasteless, colourless, weightless entity called phlogiston. The idea was that phlogiston causes things to burn, reducing them to their pure form. For example, burning wood releases phlogiston, leaving the pure form of wood – ash, therefore wood is composed of ash (pure wood) and phlogiston.
Phlogiston was accepted as scientific truth, paralysing the scientific community’s ability to discover more, true elements. One scientist even claimed to have isolated phlogiston.
Henry Cavendish and Inflammable Air
A major shareholder in the Bank of EnglandBank of England
The Bank of England is the central bank of the United Kingdom and the model on which most modern central banks have been based. Established in 1694, it is the second oldest central bank in the world...
with royal connections, Henry Cavendish
Henry Cavendish
Henry Cavendish FRS was a British scientist noted for his discovery of hydrogen or what he called "inflammable air". He described the density of inflammable air, which formed water on combustion, in a 1766 paper "On Factitious Airs". Antoine Lavoisier later reproduced Cavendish's experiment and...
was a painfully shy character, who made the vital chemical contribution of discovering the first elemental gas.
He added some zinc to spirit of salt (hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
) and collected the evanescence given off as bubbles. The gas he collected was tasteless, odourless and colourless, and moreover it produced a squeaky pop in the presence of a flame – this lead Cavendish to name the gas inflammable air, which he believed to be one and the same as phlogiston.
Cavendish made an important observation, though little did he realise it, about burning phlogiston in air, a dewy liquid was formed on the inside of the glassware: water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
. This should have had enormous repercussions for the whole scientific community in the 1700s, who still believed water to be an elemental substance. Yet, if water could be made by burning inflammable air, then water is not an element, but a compound
Compound
Compound may refer to:* Chemical compounds, combinations of two or more elements* Compound , a cluster of buildings having a shared purpose, usually inside a fence or wall...
.
However, it simply did not occur to Cavendish that water was a compound – instead he assumed that the airs contained a form of water, which phlogiston modified into liquid, elemental water.
Phlogiston had given the Ancient Greek idea of water as an element a brief reprieve, but the Greek system was now under heavy scrutiny as the Royal Society commissioned its members to investigate the invisible airs.
Joseph Priestly and Dephlogisticated Air
By the mid 1700s there were three known ‘airs’:- Common air – the air we breathe;
- Cavendish’s inflammable air;
- Fixed air.
It was this last air which caught the attention of Joseph Priestly, a Unitarian minister whose favourite pastime was the investigation of airs – specifically, fixed air, given off by the fermentation process in breweries.
Priestly’s passion for science lead to an invitation to Bowood House
Bowood House
Bowood is a grade I listed Georgian country house with interiors by Robert Adam and a garden designed by Lancelot "Capability" Brown. It is adjacent to the village of Derry Hill, halfway between Calne and Chippenham in Wiltshire, England...
, to tutor the children of Lord Shelburne. This was an excellent opportunity, given that Priestly did not have the money of earlier chemists like Boyle and Cavendish, and would still be free to pursue his own research.
In 1774 Priestly performed a hugely important experiment: he heated mercuric calc and collected the gas given off. He discovered that this gas was able to relight the embers of a previously lit wooden splint. He concluded that the splint was introducing phlogiston to the gas, only after which could it burn, therefore the gas must be ‘without phlogiston’ – this lead Priestly to name it dephlogisticated air.
In October 1775 Priestly accompanied Lord Shelburne on a trip to Paris where they were invited to dine with the preeminent scientists of the time. It is here that Priestly met the French scientist Antoine Lavoisier
Antoine Lavoisier
Antoine-Laurent de Lavoisier , the "father of modern chemistry", was a French nobleman prominent in the histories of chemistry and biology...
.
Antone Lavoisier and the end of Phlogiston
Priestly told Lavoisier all the details of his experiments upon the production of dephlogisticated air. Unlike Priestly, Lavoisier had one of the best equipped laboratories in Europe and now turned his attention to the highly accurate measurement of the masses of substances before and after they were heated.Lavoisier weighted a sample of tin, then reweighed after he had heated it and found it had increased in mass. This was an unexpected result given that the tin was thought to have released phlogiston during the burning process. Lavoisier was struck with a ground-breaking thought – maybe the tin had absorbed something from the air, making it heavier, but if so, what?
To investigate this further, Lavoisier reran Priestly’s experiment in reverse – he heated some mercury in a sealed container until it turned into mercuric calc and measured the amount of air absorbed. He then heated the mercuric calc and measured the amount of air released and discovered the quantities were the same. Lavoisier realised that something was absorbed from the air when mercury was heated to make mercuric calc, and that same gas was released when the mercuric calc was heated. Lavoisier concluded that this gas was unrelated to phlogiston, but was in fact a brand new element, which he named oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
.
Lavoisier had successfully dispensed with the need for the theory of phlogiston and recognised Priestly’s ‘dephlogisticated air’ as the element oxygen. Despite the fact it was Priestly’s original work that laid the foundations for his discovery, Lavoisier claimed he had discovered oxygen; Priestly, after all, had failed to recognise it as a new element.
Lavoisier went on to give science its first definition of an element: a substance that cannot be decomposed by existing chemical means. He also set about drawing up a list of all the elements – now 33 elements replaced the ancient four. His list was grouped into four categories: gases, non-metals, metals and earths.
On top of this, Lavoisier created a classification system for the ever increasing array of chemicals being discovered. As mentioned, ‘dephlogisticated air’ became oxygen, ‘inflammable air’ became hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
, but the nomenclature of compounds was also put on a more logical footing as ‘oil of vitriol’ became sulphuric acid, ‘philosophical wool’ became zinc oxide and ‘astringent mars saffron’ became iron oxide.
Unfortunately, whilst Lavoisier had rid the world of the phlogiston paradigm, he introduced two new erroneous elements now known to be pure energy: lumière and calorique; light and heat.
In revenge for his sympathies with the revolutionaries in France, Priestly’s home in England was targeted by arsonists in 1791, luckily he escaped thanks to a tip-off, but decided to flee to America. Lavoisier’s contributions to science were cut short in 1794 by the revolutionaries, who arrested him on grounds of being an enemy of the French people, and had him guillotined.
Humphrey Davy and Potash
In 1807, the Professor of Chemistry at the Royal Institution in London was the Cornishman Humphrey Davy. He was investigating crystalline salts of potashPotash
Potash is the common name for various mined and manufactured salts that contain potassium in water-soluble form. In some rare cases, potash can be formed with traces of organic materials such as plant remains, and this was the major historical source for it before the industrial era...
because he was unconvinced potash was an element, but by the end of the previous century, Lavoisier had been unable to break it down further.
Since then however, the first electric battery
Voltaic pile
A voltaic pile is a set of individual Galvanic cells placed in series. The voltaic pile, invented by Alessandro Volta in 1800, was the first electric battery...
had recently been invented (rows of metal plates and cardboard soaked in saltwater). Although scientists were aware that the production of a continuous electric current was due to some property of the metals, Davy believed that a chemical reaction was taking place. If that was true, then maybe the reverse was also true: an electric current could cause a chemical reaction.
Davy heated the potash until it was liquid, then introduced two electrodes and passed a current through the molten potash. A lilac flame was observed, the result of successfully breaking down potash into its constituent elements – one of which, was the previously never before seen element potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
.
Davy went on to add six new elements to Lavoisier’s list, as well as confirming that substances like chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
and iodine
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
were also elements. By the time of his death in 1829 the idea of the elements was firmly established, 55 separate elements had been discovered, and the world had a new science: Chemistry.
Introduction
At the beginning of the 19th century only 55 of the 92 naturally occurring elements had been discovered. Scientists had no idea how many more they might find, or indeed if there was an infinite number of elements. They also sought to answer a fundamental question, namely: is there a pattern to the elements?John Dalton’s Atoms
Scientists had recently discovered that when elements combine to form compounds, they always do so in the same proportions, by weight. John DaltonJohn Dalton
John Dalton FRS was an English chemist, meteorologist and physicist. He is best known for his pioneering work in the development of modern atomic theory, and his research into colour blindness .-Early life:John Dalton was born into a Quaker family at Eaglesfield, near Cockermouth, Cumberland,...
thought that for this to happen, each element had to be made of its own unique building blocks, which he called atoms
Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
.
Dalton suggested that everything in the universe was made of atoms, and that there are as many kinds of atoms as there are elements, each one with its own signature weight. Based on these ideas, working completely alone, Dalton attempted to impose some order on the elements by drawing up a list, where each element was represented by an alchemical-looking symbol, ordered by atomic weight
Atomic weight
Atomic weight is a dimensionless physical quantity, the ratio of the average mass of atoms of an element to 1/12 of the mass of an atom of carbon-12...
.
Although Dalton did not get all his atomic weights correct, he was pointing science in the right direction. Sadly, in the early 1800s few scientists accepted the idea that elements had different weights.
Jöns Jacob Berzelius’ Pursuit of Atomic Weights
The Swedish scientist BerzeliusBerzelius
Berzelius is a secret society at Yale University named for the Swedish scientist Jöns Jakob Berzelius, considered one of the founding fathers of modern chemistry...
was one of the few scientists who strongly believed in the idea of atomic weights, and thought that knowing as much as possible about their weights was vitally important. When he heard of Dalton’s theory, he set about the gargantuan task of measuring the atomic weight of every single known element – without any proof that Dalton’s atoms actually existed.
This was even more challenging than it first seems once you consider the fact that very little of the chemical glassware necessary for such precise measurements had been invented. Berzelius had to manufacture much of it himself.
Berzelius’ experiences with glass-blowing had an additional bonus, in 1824 he discovered that one of the constituents of glass was a new element – silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
. Having already discovered three other elements prior to silicon: thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....
, cerium
Cerium
Cerium is a chemical element with the symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air. Cerium was named after the dwarf planet . Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight...
and selenium
Selenium
Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...
, Berzelius spent the next ten years obsessively measuring more than two thousand chemical compounds in pursuit of accurate atomic weights for the elements. Eventually Berzelius had remarkably accurate atomic weights for 45 elements; his value for chlorine was accurate to within 0.2% of the value we know today.
However, by the time Berzelius had produced his results, other scientists were now measuring atomic weights – and getting conflicting results. In fact, scientists were looking for all sorts of patterns throughout the elements.
Johann Döbereiner’s Triads
One such pattern hunter was German chemist Johann Döbereiner. He believed the key to understanding the elements lay not with their atomic weights but with their chemical properties. He noticed that one could often single out three elements that exhibited similar properties, such as the alkali metals, which he called triads.The problem was that Döbereiner’s triads only worked for a few of the elements and got scientists no further than atomic weights.
Dmitri Mendeleev moves to St Petersburg
In 1848 a huge fire destroyed the factory of the widow Maria Mendeleeva. Facing destitution she decided to embark on the 1,300 mile journey from Western SiberiaSiberia
Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...
to St Petersburg – walking a significant portion of the route – so her son Dmitri Mendeleev
Dmitri Mendeleev
Dmitri Ivanovich Mendeleev , was a Russian chemist and inventor. He is credited as being the creator of the first version of the periodic table of elements...
could continue his education in the capital of the Russian Empire
Russian Empire
The Russian Empire was a state that existed from 1721 until the Russian Revolution of 1917. It was the successor to the Tsardom of Russia and the predecessor of the Soviet Union...
.
At the time the scientific community was grappling with the problem of how to bring order to the 63 elements that were now known. Mendeleev was still a student when he attended the world’s first international chemistry conference – convened to settle the confusion surrounding atomic weights.
Stanislao Cannizzaro’s Standard for Measuring Atomic Weights
SicilianSicily
Sicily is a region of Italy, and is the largest island in the Mediterranean Sea. Along with the surrounding minor islands, it constitutes an autonomous region of Italy, the Regione Autonoma Siciliana Sicily has a rich and unique culture, especially with regard to the arts, music, literature,...
chemist Stanislao Cannizzaro
Stanislao Cannizzaro
Stanislao Cannizzaro, FRS was an Italian chemist. He is remembered today largely for the Cannizzaro reaction and for his influential role in the atomic-weight deliberations of the Karlsruhe Congress in 1860.-Biography:...
was still convinced that atomic weights held the key to the order of the elements and had found a new way of measuring them. Cannizzaro knew that equal volumes of gases contain equal numbers of particles, therefore instead of working with solids and liquids and all the unreliability that entails, he proposed measuring the densities of gases to measure the weights of individual gaseous atoms.
Whereas Berzelius’ results had failed to convince anyone, Cannizzaro’s method set an agreed standard for measuring atomic weights accurately. Chemists soon found that even with accurate atomic weights, the elements still seemed unordered, but then, a solitary English chemist made a curious discovery.
John Newland’s Octaves
In 1863 John NewlandsJohn Newlands
John Newlands may refer to:*John Alexander Reina Newlands , English analytical chemist*John Newlands , Australian Senator...
noticed that when ordered by weight, every eighth element seemed to share similar properties, such as carbon and silicon in the sequence: carbon, nitrogen, oxygen, fluorine, sodium, magnesium and silicon. He called this a Law of Octaves.
Three years later, in 1866, he presented his ideas to the Chemical Society
Chemical Society
The Chemical Society was formed in 1841 as a result of increased interest in scientific matters....
, unfortunately for Newlands, the musical analogy was not well received – the audience suggesting he might as well have ordered the elements alphabetically.
Today, Newland’s Octaves are known as the Law of Periodicity, and Mendeleev was thinking along the same lines.
Mendeleev’s Periodic Table
By 1869 Mendeleev had been trying to find an order for the elements for a decade. One day he struck upon the idea of making up a pack of cards with the elements’ names on and began playing a game he called ‘chemical solitaire’. He began laying out the cards, over and over, just to see if he could form a pattern where everything fitted together.To date, chemist had tried to group elements in one of two ways:
- By their atomic weights (Berzelius’ and Cannizzaro’s Atomic Weights);
- By their chemical properties (Döbereiner’s Triads and Newland’s Octaves).
Mendeleev’s genius was to combine those two methods together. However, the odds were stacked against him – little more than half the known element had been discovered: he was playing with an incomplete deck of cards.
He stayed up for three days and nights then, finally, on 17 February 1869, he fell asleep and dreamt of all 63 known elements laid out in a grand table
Periodic table
The periodic table of the chemical elements is a tabular display of the 118 known chemical elements organized by selected properties of their atomic structures. Elements are presented by increasing atomic number, the number of protons in an atom's atomic nucleus...
.
Mendeleev’s table reveals the relationship between all the elements in their order:
- Atomic weights increase reading from left to right;
- Triads and Octaves are visible reading down the columns.
Notice carbon and silicon are in Group IV and the volatile gases fluorine, chlorine and bromine are in Group VII.
Mendeleev was sufficiently confident in the layout of his table that he was willing to leave gaps for unknown elements to make the pattern fit – believing other elements would later be discovered that filled the gaps.
- After Calcium (Ca, weight 40) he left a gap, predicting a metallic element slightly heavier than calcium;
- After Zinc (Zn, weight 65) he left a gap, predicting a metal with a low melting point and atomic weight 68;
- Immediately after that gap, he left a further gap, predicting another metal, dark grey in colour.
So, for Mendeleev to be vindicated, the gaps needed to be filled, and luckily, in 1859, new instrumentation had been developed for discovering elements.
Bunsen’s Burner and Kirchhoff’s Spectrometer
Robert BunsenRobert Bunsen
Robert Wilhelm Eberhard Bunsen was a German chemist. He investigated emission spectra of heated elements, and discovered caesium and rubidium with Gustav Kirchhoff. Bunsen developed several gas-analytical methods, was a pioneer in photochemistry, and did early work in the field of organoarsenic...
knew that when certain elements burned in the flames of his burner they each turned the flame a different colour. Copper burned green, strontium red and potassium lilac – Bunsen wondered if every element had a unique colour.
Bunsen was joined in his research by Gustav Kirchhoff
Gustav Kirchhoff
Gustav Robert Kirchhoff was a German physicist who contributed to the fundamental understanding of electrical circuits, spectroscopy, and the emission of black-body radiation by heated objects...
. Kirchhoff used the concept of the dispersion of white light by a prism in the invention of the spectroscope, a device with a prism at its centre which split the light from Bunsen’s flames into distinct bands of its constituent colours – the element’s spectral lines.
Kirchhoff and Bunsen realised these spectral lines were unique to each element, and, using this technique they discovered two new elements, caesium and rubidium.
Paul Emile Lecoq de Boisbaudran discovers Gallium
In 1875 the Parisian chemist Paul Emile Lecoq de BoisbaudranPaul Emile Lecoq de Boisbaudran
Paul Émile Lecoq de Boisbaudran was a French chemist known for his discoveries of the chemical elements gallium, samarium and dysprosium.-Biography:...
used a spectroscope to discover a new metallic element. It was a silvery-white, soft metal with an atomic weight of 68, which he named gallium
Gallium
Gallium is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies...
, after his native France. It also turned out to have a very low melting point, thus matching all the expected properties of the element Mendeleev expected to fill the gap he had left after zinc; indeed, this is exactly where the element was placed in the periodic table.
Even though Mendeleev had left the necessary gap for gallium as well as other elements, it was becoming clear there was an entire group that was missing altogether.
Pierre Janssen and Norman Lockyer discover Helium
In 1868, the French astronomer Pierre Janssen travelled to India in time for the total solar eclipseSolar eclipse
As seen from the Earth, a solar eclipse occurs when the Moon passes between the Sun and the Earth, and the Moon fully or partially blocks the Sun as viewed from a location on Earth. This can happen only during a new moon, when the Sun and the Moon are in conjunction as seen from Earth. At least...
that occurred in August of that year. As well as his telescope, he also went equipped with a spectroscope, to study the spectral lines of the light emitted from the sun. Normally, due to the intensity of sunlight many weaker spectral lines are not visible next to the extreme brightness of the stronger lines. Janssen hoped that he would observe more spectral lines during the eclipse when the sun’s light was less intense.
The eclipse allowed Janssen to observe a spectral line never seen before, which was not associated with any known element. The same spectral line was confirmed by the English astronomer Norman Lockyer, who thinking the element only existed in the sun, named it helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
, after the Greek Sun God.
However, it wasn’t long before another British scientist had discovered helium on Earth.
William Ramsay discovers the noble gases
By dissolving the radioactive ore cleveite in acid, William RamseyWilliam Ramsey
William Ramsey may refer to:*William Marion Ramsey , American politician and judge in Oregon*William of Ramsey, 13th century English Benedictine monk of Croyland Abbey*William Ramsey , 14th century English architect...
was able to collect a gas trapped within the rock, which had an atomic weight of 4, and the same spectral lines which Lockyer had observed: helium. Prior to this, Ramsay had already isolated a new gas from the atmosphere; argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
, with an atomic weight of 40.
A problem now arose – Mendeleev had not left any gaps which were suitable for either of these two new elements, which lead Ramsay to conclude an entire group was missing from the periodic table – only two of whose members were now known to exist, helium and argon.
Ramsey successfully discovered all the other stable elements in the group which he named neon
Neon
Neon is the chemical element that has the symbol Ne and an atomic number of 10. Although a very common element in the universe, it is rare on Earth. A colorless, inert noble gas under standard conditions, neon gives a distinct reddish-orange glow when used in either low-voltage neon glow lamps or...
(Greek for new), krypton
Krypton
Krypton is a chemical element with the symbol Kr and atomic number 36. It is a member of Group 18 and Period 4 elements. A colorless, odorless, tasteless noble gas, krypton occurs in trace amounts in the atmosphere, is isolated by fractionally distilling liquified air, and is often used with other...
(Greek for hidden) and xenon
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...
(Greek for stranger). All the elements of this new group had one overwhelming characteristic; their lack of reactivity. It was this particular characteristic that brought to mind a name for the new group: the noble gases.
Mendeleev vindicated
Mendeleev’s periodic table had brought order to all the elements, allowing him to make predictions that future scientists tested and found to be true. By the time he died he was world-renowned in chemistry. His periodic table was set in stone in St Petersburg and an element was eventually named after him: mendeleviumMendelevium
Mendelevium is a synthetic element with the symbol Md and the atomic number 101. A metallic radioactive transuranic element in the actinide series, mendelevium is usually synthesized by bombarding einsteinium with alpha particles. It was named after Dmitri Ivanovich Mendeleev, who created the...
.
The periodic table does not however tell us why some elements are highly reactive, others completely inert, why some are volatile, whilst others less so. It wasn’t until the beginning of the 20th century that an entirely different branch of science began to unravel the answers to these questions.
Niels Bohr’s fixed shell model
In 1909, the physicist, Ernest RutherfordErnest Rutherford
Ernest Rutherford, 1st Baron Rutherford of Nelson OM, FRS was a New Zealand-born British chemist and physicist who became known as the father of nuclear physics...
proposed the structure of the atom was like that of a solar system: mostly empty space with electrons floating around a dense nucleus.
Subsequently the Danish Physicist Niels Bohr
Niels Bohr
Niels Henrik David Bohr was a Danish physicist who made foundational contributions to understanding atomic structure and quantum mechanics, for which he received the Nobel Prize in Physics in 1922. Bohr mentored and collaborated with many of the top physicists of the century at his institute in...
introduced the idea that electrons occupied “fixed shells” around the nucleus, which was further developed when it was suggested that each such shell could only accommodate a fixed number of electrons: 2 in the first shell; 8 in the second shell; 18 in the third shell, and so on, each shell holding an increasing number of electrons.
The chemical behaviour of all elements is explained by the number of electrons in their outer shells: to increase the energetic stability of their electron configurations atoms have a tendency to gain or lose electrons in such a way so as to achieve a full outer shell. Sodium, with 11 electrons – one in its outer-most occupied shell, will transfer an electron in the presence of fluorine to its outer-most occupied shell, which contains seven electrons. The result is both sodium and fluorine now have a full outer shell, and Sodium Fluoride is formed.
This theory explained why all elements react in the way they do and why some formed the compounds they do, while others did not. It also explained why elements had the physical properties they did, which in turn explained why the periodic table had the shape it did. However, there was one fundamental question left unanswered: how many elements were there – could there be an infinite number of elements between Hydrogen and Uranium?
Henry Moseley’s proton numbers
Early 20th century chemist Henry MoseleyHenry Moseley
Henry Gwyn Jeffreys Moseley was an English physicist. Moseley's outstanding contribution to the science of physics was the justification from physical laws of the previous empirical and chemical concept of the atomic number. This stemmed from his development of Moseley's law in X-ray spectra...
speculated that the answer to the number of elements lay in the nucleus. By firing a radioactive source at copper, he was able to knock electrons from their atoms, releasing a burst of energy in the form of an x-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
. When measured, the x-rays always had the same energy, unique to copper. He discovered each element released x-rays of different energies. Moseley’s brilliance was to realise the x-ray energy is related to the number of protons inside the atom: the atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
.
Because this is the number of protons, the atomic number must be a whole number – there cannot be any fractional values. Mosley realised it was the atomic number, not the atomic weight that determines the order of the elements. What’s more, because the atomic number increases in whole numbers from one element to the next there can be no extra elements between Hydrogen (atomic number 1) and Uranium (atomic number 92) – there can only be 92 elements, there is no room for any more.
Moseley was just 26 when he completed this research. Aged 27 he was killed in action during the First World War – shot through the head by a sniper.
Introduction
Just 92 elements combine to form all the compounds on Earth. Iron, when combined with chromium, carbon and nickel makes stainless steelStainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
. Glass is made of silicon and oxygen.
Since prehistoric times, people have been engaging in ‘bucket chemistry’ – adding all sorts of chemicals together, just to see what would happen. As a result, many early discoveries in chemistry were accidental.
Heinrich Diesbach produces the first synthetic paint
In 18th century PrussiaPrussia
Prussia was a German kingdom and historic state originating out of the Duchy of Prussia and the Margraviate of Brandenburg. For centuries, the House of Hohenzollern ruled Prussia, successfully expanding its size by way of an unusually well-organized and effective army. Prussia shaped the history...
, Heinrich Diesbach
Heinrich Diesbach
Heinrich Diesbach was a German painter and colormaker known for his accidental discovery of a method for making a blue known as Prussian blue, AKA iron blue, Berlin blue....
was trying to produce a synthetic red paint. He started by heating potash (potassium carbonate), with no idea that his potash had been contaminated with blood. When heated, the proteins in blood are altered, allowing them to combine with the iron in the blood, whilst the carbonate reacts with the haemoglobin to produce a solid.
After heating the resulting solid to an ash, filtering and diluting, Diesbach added green vitriol (iron sulphate) to create a complex ion: ferric ferrocyanide. Finally, adding sprit of salt (hydrochloric acid) draws out a brilliant colour: Prussian Blue
Prussian blue
Prussian blue is a dark blue pigment with the idealized formula Fe718. Another name for the color Prussian blue is Berlin blue or, in painting, Parisian blue. Turnbull's blue is the same substance but is made from different reagents....
.
Justus von Liebig and Friedrich Wöhler encounter isomerism
Ever since seeing fireworks as a child, another German chemist, Justus von LiebigJustus von Liebig
Justus von Liebig was a German chemist who made major contributions to agricultural and biological chemistry, and worked on the organization of organic chemistry. As a professor, he devised the modern laboratory-oriented teaching method, and for such innovations, he is regarded as one of the...
, had become obsessed with trying to better understand the elements by creating explosive combinations. Specifically, he was interested in the explosive compound silver fulminate.
In 1825 he read a paper written by Friedrich Wöhler
Friedrich Wöhler
Friedrich Wöhler was a German chemist, best known for his synthesis of urea, but also the first to isolate several chemical elements.-Biography:He was born in Eschersheim, which belonged to aau...
in which he describes a compound called silver cyanate, made in equal parts of silver, carbon, nitrogen and oxygen, which he described as harmless and stable. von Liebig immediately wrote back a furious letter condemning Wöhler as a hopeless analyst: those elements combined in equal proportions were exactly what made the explosive silver fulminate.
Instead of backing down, Wöhler challenged von Liebig to make silver cyanate for himself. The results would have astounded him – the same elements that combined according to von Liebig’s method, when combined according to Wöhler’s method made two completely different compounds.
Wöhler and von Liebig had inadvertently discovered isomerism: the same number of atoms of the same elements combining in different ways to make different compounds. In time, this would explain how just 92 elements could make the vast array of compounds we know today.
Chemists started to realise that understanding the arrangement of atoms within compounds was crucial if they wished to design new compounds, and the first step in this direction was taken by studying carbon.
Smithson Tennant discovers what diamonds are made of
In 1796 Smithson TennantSmithson Tennant
Smithson Tennant FRS was an English chemist.Tennant is best known for his discovery of the elements iridium and osmium, which he found in the residues from the solution of platinum ores in 1803. He also contributed to the proof of the identity of diamond and charcoal. The mineral tennantite is...
was experimenting on diamonds when he decided to burn one. Using only sunlight and a magnifying glass he managed to ignite a diamond sufficiently for it to produce a gas, which he collected and was able to identify as carbon dioxide.
Having started with only diamond and oxygen, and produced a gas which contains only carbon and oxygen, Tennant had discovered that diamonds are made of carbon.
Unaware of atomic theory at the time, scientists were unable to explain how carbon, already known to exist as one of the softest substances in the form of graphite
Graphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
, could also be the sole constituent element of the hardest known substance: diamond
Diamond
In mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions...
.
Exactly 50 years later, a young Scottish chemist discovered there are no prizes in Science for coming second.
Archibald Scott Couper formulates the theory of chemical bonds
In 1856 Archibald Scott CouperArchibald Scott Couper
Archibald Scott Couper was a Scottish chemist who proposed an early theory of chemical structure and bonding...
went to work for a French chemist, Charles-Adolphe Wurtz
Charles-Adolphe Wurtz
Adolphe Wurtz was an Alsatian French chemist. He is best remembered for his decades-long advocacy for the atomic theory and for ideas about the structures of chemical compounds, against the skeptical opinions of chemists such as Marcellin Berthelot and Etienne Henri Sainte-Claire Deville...
. Whilst in Paris he came up with the idea of links between atoms that could explain how individual atoms formed compounds. He called these links bonds. Somehow, Couper realised that carbon can form four bonds, thereby attaching itself with different strengths to other carbon atoms in a compound:
- In diamond all four bonds are connected to other carbon atoms in three-dimensions, making it so hard.
- In graphite only three bonds are connected to other carbon atoms in a two-dimensional hexagonal lattice, allowing layers to slide over each other, making graphite soft.
The ability of carbon to form four bonds also means it can exist in a huge variety of chemical structures, such as long chains and even rings, making it a rarity amongst the elements. This helped to explain the abundance of carbon in all life forms, from protein and fat, to DNA and cellulose, and why carbon exists in more compounds than any other element.
All that remained for Couper was to get his paper published...
Friedrich Kekulé formulates the same theory of chemical bonds
Friedrich Kekulé was a German scientist who spent some time studying in London. It was apparently whilst riding a London bus he struck upon the idea of atoms ‘holding hands’ to form long chains. Kekulé rushed to compose a paper formalising his ideas on an equivalent theory of chemical bonds.Meanwhile in Paris, Wurtz had been slow to publish Couper’s paper and Kekulé, whose work appeared in print first, claimed all the credit. When Couper discovered Wurtz had delayed in sending his paper to be published he flew into a rage and was promptly expelled from the laboratory by Wurtz.
The crushing disappointment at having lost out on his chance of scientific recognition led him first to withdraw from Science and then to suffer a nervous breakdown. He spent years in and out of an asylum.
However, now that scientists were beginning to understand the way carbon combines with itself and other elements, it was possible to create new compounds by design and industrial chemistry was born.
Wallace Carothers invents nylon
Two decades after the world’s first plastic – Bakelite – had been invented in 1907, Wallace CarothersWallace Carothers
Wallace Hume Carothers was an American chemist, inventor and the leader of organic chemistry at DuPont, credited with the invention of nylon....
successfully drew off a fibre from the interface of two liquids: hexane-1,6-diamine and decanedioyl-dichloride, which could be spun into a very fine, very strong thread. It was given the name nylon
Nylon
Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station...
.
Shockingly, only three weeks after the patent for nylon had been filed, a depressed Carothers slipped another carbon based compound into his own drink, potassium cyanide, and killed himself.
Evidently, industrial chemistry wasn’t without its downsides, and one chemist was arguably responsible for single-handedly polluting the entire Earth with lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
.
Thomas Midgley Junior prevents engines from knocking
In his capacity as an engineer with General MotorsGeneral Motors
General Motors Company , commonly known as GM, formerly incorporated as General Motors Corporation, is an American multinational automotive corporation headquartered in Detroit, Michigan and the world's second-largest automaker in 2010...
, Thomas Midgley
Thomas Midgley
Thomas Midgley was an English professional footballer who played as an inside forward. Born in the town of Burnley, Lancashire, he initially played rugby union for the Burnley Rovers club before they changed codes to association football in May 1882 and changed their name to Burnley...
experimented with a myriad of different compounds, which he added to petrol in an attempt to prevent engines from knocking. Eventually, he discovered one compound that worked brilliantly: tetra-ethyl lead
Tetra-ethyl lead
Tetraethyllead , abbreviated TEL, is an organolead compound with the formula 4Pb. An inexpensive additive, its addition to gasoline from the 1920's allowed octane ratings and thus engine compression to be boosted significantly, increasing power and fuel economy...
.
By the 1970s the use of leaded petrol was ubiquitous worldwide, but research was emerging about the damage that it was doing to humans and the environment. In 1983, a Royal Commission
Royal Commission
In Commonwealth realms and other monarchies a Royal Commission is a major ad-hoc formal public inquiry into a defined issue. They have been held in various countries such as the United Kingdom, Australia, Canada, New Zealand, and Saudi Arabia...
asked the question: “Is there any part of the Earth’s surface, or any form of life that remains uncontaminated?”
Today nearly all petrol is unleaded, although lead lives on in motor vehicles in their batteries.
Henri Becquerel discovers radioactivity
In 1896 the French scientist Henri BecquerelHenri Becquerel
Antoine Henri Becquerel was a French physicist, Nobel laureate, and the discoverer of radioactivity along with Marie Curie and Pierre Curie, for which all three won the 1903 Nobel Prize in Physics.-Early life:...
was working with uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
crystals when he found UV light made them glow. Leaving the uranium crystals on an unexposed photographic plate overnight, he returned the next morning to discover they had caused the part of the plate they were sat on to develop.
Becquerel correctly reasoned the only source of energy that could have caused this was the crystals themselves. He had discovered radioactivity, and a young Polish scientist began to investigate.
Marie Curie investigates radioactivity
Marie CurieMarie Curie
Marie Skłodowska-Curie was a physicist and chemist famous for her pioneering research on radioactivity. She was the first person honored with two Nobel Prizes—in physics and chemistry...
began her investigations by testing a uranium ore called pitchblende with an electrometer. She discovered it was four times more radioactive than pure uranium, and wondered if this was due to the presence of an even more radioactive element in the pitchblende.
Curie began stockpiling tonnes of pitchblende, then in the most basic of workshops with primitive equipment she undertook a multitude of complex and dangerous procedures in an attempt to isolate this new element.
In the event, Curie discovered two new elements, polonium
Polonium
Polonium is a chemical element with the symbol Po and atomic number 84, discovered in 1898 by Marie Skłodowska-Curie and Pierre Curie. A rare and highly radioactive element, polonium is chemically similar to bismuth and tellurium, and it occurs in uranium ores. Polonium has been studied for...
named after her native Poland and radium
Radium
Radium is a chemical element with atomic number 88, represented by the symbol Ra. Radium is an almost pure-white alkaline earth metal, but it readily oxidizes on exposure to air, becoming black in color. All isotopes of radium are highly radioactive, with the most stable isotope being radium-226,...
. Whilst these were naturally occurring elements, they fuelled a scientific desire to create entirely new, artificial elements.
Ernest Rutherford explains radioactivity
At the beginning of the 20th century it was widely believed that atoms never change: an atom of one element stayed that way forever. RutherfordErnest Rutherford
Ernest Rutherford, 1st Baron Rutherford of Nelson OM, FRS was a New Zealand-born British chemist and physicist who became known as the father of nuclear physics...
had already revealed the structure of an atom to consist mostly of empty space with a dense nucleus of protons at the centre, and Henry Mosley had shown that it is the number of protons that gives an atom its identity as a particular element. An atom of the element carbon has 6 protons, whilst an atom with 7 protons is one of nitrogen.
Rutherford came to the conclusion that the number of protons in a radioactive element could change – through a process of decay where parts of the nucleus are ejected from the atom. Rutherford named these fragments of ejected nucleus alpha particles.
Rutherford realised that if an atom is losing protons, its identity is changing at the same time, since an atom’s identity is governed by its proton number. Radioactive decay causes atoms of one element to transmute into atoms of a different element. He then sought to artificially engineer a specific transmutation.
Rutherford fixed a source of alpha particles – each of which contains two protons – at one end of a cylindrical chamber. At the other end he fixed a screen. Each time an alpha particle reached the screen it produced a flash. He then introduced nitrogen into the chamber and observed additional, different flashes on the screen. Occasionally, an alpha particle would collide with a nitrogen nucleus and get absorbed by it, knocking out a proton in the process. These protons then travelled on through the chamber to the screen to produce the additional flashes.
However, the nucleus of nitrogen – having absorbed two protons but lost only one – had gained a proton and become a nucleus of oxygen. Rutherford’s work gave hope to scientists trying to create new elements, but one final discovery about the atom was necessary.
In 1932 the Cambridge scientist James Chadwick
James Chadwick
Sir James Chadwick CH FRS was an English Nobel laureate in physics awarded for his discovery of the neutron....
discovered the neutron – electrically neutral particles which also sit inside the nucleus along with the protons.
Enrico Fermi claims to have made elements heavier than uranium
Now in Italy, Enrico FermiEnrico Fermi
Enrico Fermi was an Italian-born, naturalized American physicist particularly known for his work on the development of the first nuclear reactor, Chicago Pile-1, and for his contributions to the development of quantum theory, nuclear and particle physics, and statistical mechanics...
– nicknamed ‘the pope’ by his colleagues for his infallibility, realised the potential of the newly discovered neutron in the search for elements heavier than uranium. Until now, scientists had been bombarding uranium with alpha particles in the hope they would enter the nucleus. Unfortunately, this was very unlikely because both alpha particles and nuclei are positively charged – the alpha particles could never overcome the electrostatic repulsion of the nucleus.
Fermi reasoned that because neutrons carried no electric charge, they would have a much better chance of penetrating the nucleus of a uranium atom. So Fermi set about firing neutrons at uranium. Fermi thought that this, coupled with his knowledge of beta decay
Beta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...
, whereby an unstable nucleus attempts stabilisation by converting one neutron to a proton and ejecting a newly formed electron, would result in an element with one extra proton than uranium: element 93.
Indeed, Fermi discovered elements he did not recognise. He tested for elements below uranium in the periodic table: radon, actinium, polonium, as far back as lead – it was none of these. So, in 1934, the infallible Fermi declared to the world he had created elements heavier than uranium.
Otto Hahn disproves Fermi’s claims
In 1938, a team of German scientists, led by Otto HahnOtto Hahn
Otto Hahn FRS was a German chemist and Nobel laureate, a pioneer in the fields of radioactivity and radiochemistry. He is regarded as "the father of nuclear chemistry". Hahn was a courageous opposer of Jewish persecution by the Nazis and after World War II he became a passionate campaigner...
, decided to investigate Fermi’s bold claim. Unfortunately for Fermi, they quickly disproved his assertion; one of the elements produced was barium
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
, which, with 56 protons, was nowhere near the 92 protons the nucleus started with when it was uranium.
Hahn wrote of his confusion to his colleague Lisa Meitner who, as an Austrian Jew, had recently fled Nazi Germany for Sweden.
Lisa Meitner explains Fermi’s work
Over Christmas 1938, Meitner considered the problem of the uranium nucleus, which she reasoned, given its relative size, must be quite unstable. She decided to model the nucleus as a drop of water, ready to divide with the impact of a single neutron. She realised the nucleus had split in half, and both Fermi and Hahn had witnessed what is now known as nuclear fissionNuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...
.
However, in doing the calculations for such an event, Meitner was unable to make the equations balance. She calculated that the products of the fission reaction were lighter than the initial uranium, by about one fifth of a proton. Somehow, a small amount of mass had disappeared. Then slowly, the solution to this discrepancy occurred to Meitner – Einstein and E = mc2
Mass-energy equivalence
In physics, mass–energy equivalence is the concept that the mass of a body is a measure of its energy content. In this concept, mass is a property of all energy, and energy is a property of all mass, and the two properties are connected by a constant...
– the missing mass had been converted to energy.
The Manhattan Project
Meitner’s work was published in 1939, but as well generating interest amongst the scientific community, Meitner’s revelations were also coming to the attention of governments on the verge of war. Fuelled by fears Nazi Germany was investigating nuclear weapons of its own, scientists were assembled in America to work on the Manhattan ProjectManhattan Project
The Manhattan Project was a research and development program, led by the United States with participation from the United Kingdom and Canada, that produced the first atomic bomb during World War II. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the US Army...
aimed at creating the first atomic bomb.
For an explosion to occur, there must be a rapid release of energy – a slow release of energy from uranium nuclei would give a uranium fire, but no explosion. Both sides poured their effort into creating the necessary conditions for a chain reaction
Chain reaction
A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback leads to a self-amplifying chain of events....
.
In 1942 Enrico Fermi, now living in America, successfully induced a chain reaction in uranium, but processing uranium for bombs was both difficult and costly. America had just come up with a different solution to win the atomic race.
Now finally, scientists’ dream of creating an element beyond the end of the periodic table was about to be realised.
Edwin McMillian and Phillip Ableson create the first synthetic element
In California, scientists were trying to create a new element heavier than uranium using cyclotron machines. This involved using huge magnets to steer atoms round in circles faster and faster until they reached a tenth of the speed of light, whereupon they were smashed into a uranium target.Edwin McMillian and Phillip Ableson blasted uranium with a beam of particles to create the first synthetic element, heavier than uranium – element 93, which they named neptunium
Neptunium
Neptunium is a chemical element with the symbol Np and atomic number 93. A radioactive metal, neptunium is the first transuranic element and belongs to the actinide series. Its most stable isotope, 237Np, is a by-product of nuclear reactors and plutonium production and it can be used as a...
.
The next synthetic element, plutonium
Plutonium
Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...
, quickly followed in 1941, which scientists realised was readily able to undergo fission in a way capable of producing the desired chain reaction. It was soon being made into a bomb.
A mere seven years after the discovery of nuclear fission, on 6th August 1945, half a gram of uranium was converted into energy when the world’s first atomic bomb was dropped on Hiroshima
Hiroshima
is the capital of Hiroshima Prefecture, and the largest city in the Chūgoku region of western Honshu, the largest island of Japan. It became best known as the first city in history to be destroyed by a nuclear weapon when the United States Army Air Forces dropped an atomic bomb on it at 8:15 A.M...
. As Lisa Meitner’s calculations suggested, this conversion released energy equivalent to 13,000 tonnes of TNT. A plutonium bomb was dropped on Nagasaki
Nagasaki
is the capital and the largest city of Nagasaki Prefecture on the island of Kyushu in Japan. Nagasaki was founded by the Portuguese in the second half of the 16th century on the site of a small fishing village, formerly part of Nishisonogi District...
three days later.
GSI Helmholtz Centre for Heavy Ion Research
Using one of the world’s largest particle accelerators, scientists working at the Heavy Ion Research facility in Darmstadt, Germany, have so far confirmed the existence of element 112, which they have named copernicium, after Polish astronomer Nicholas Copernicus.These physicists have become the new chemists – testing the foundations of the periodic table, and hence our understanding of the universe, in light of new discoveries.
In addition to producing new elements, scientists are also attempting to discern their properties. Copernicium is found to be a volatile metal that would be liquid at room temperature if enough were ever made – exactly what Mendeleev would predict for element 112 – which sits directly beneath mercury in the periodic table.
See also
- The Story of MathsThe Story of MathsThe Story of Maths is a British television series outlining aspects of the history of mathematics. The series was a co-production between the Open University and the BBC and aired in October 2008 on BBC Four. The material was written and presented by Oxford professor Marcus du Sautoy...
- The Story of Science: Power, Proof and PassionThe Story of Science: Power, Proof and PassionThe Story of Science: Power, Proof and Passion is a 2010 BBC documentary on the history of science presented by Michael J. Mosley.- Episodes :- External links :*...
- Botany: A Blooming History
- Shock and Awe: The Story of Electricity Shock and Awe: The Story of ElectricityShock and Awe: The Story of Electricity is a British television series outlining aspects of the history of electricity. The series was a co-production between the Open University and the BBC and aired in October 2011 on BBC Four...