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Valence (chemistry)
Encyclopedia
In chemistry
, valence, also known as valency or valence number, is a measure of the number of bonds
formed by an atom of a given element. "Valence" can be defined as the number of valence bonds
a given atom has formed, or can form, with one or more other atoms. For most elements the number of bonds can vary. The IUPAC
definition limits valence to the maximum number of univalent atoms that may combine with the atom, that is the maximum number of valence bonds that is possible for the given element.
The valence of an element depends on the number of valence electron
s that may be involved in the forming of valence bonds. A univalent (monovalent) atom, ion or group has a valence of one and thus can form one covalent bond
. A divalent
molecular entity
has a valence of two and can form two sigma bonds to two different atoms or one sigma bond
plus one pi bond
to a single atom.
Alkyl groups and hydroxyl
ions are univalent examples; oxo ligand
s are divalent.
Over the last century, the concept of valence evolved into a range of approaches for describing the chemical bond, including Lewis structure
s (1916), valence bond theory
(1927), molecular orbital
s (1928), valence shell electron pair repulsion theory
(1958) and all the advanced methods of quantum chemistry
.
of the word "valence" traces back to 1425, meaning "extract, preparation," from Latin valentia "strength, capacity," and the chemical meaning referring to the "combining power of an element" is recorded from 1884, from German Valenz.
In 1789, William Higgins
published views on what he called combinations of "ultimate" particles, which foreshadowed the concept of valency bonds. If, for example, according to Higgins, the force between the ultimate particle of oxygen and the ultimate particle of nitrogen were 6, then the strength of the force would be divided accordingly, and similarly for the other combinations of ultimate particles (see illustration).
The exact inception, however, of the theory of chemical valencies can be traced to an 1852 paper by Edward Frankland
, in which he combined the older theories of free radicals and “type theory” with thoughts on chemical affinity
to show that certain elements have the tendency to combine with other elements to form compounds containing 3, i.e. in the three atom groups (e.g. NO3, NH3, NI3, etc.) or 5, i.e. in the five atom groups (e.g. NO5, NH4O, PO5, etc.), equivalents of the attached elements. It is in this manner, according to Frankland, that their affinities are best satisfied. Following these examples and postulates, Frankland declares how obvious it is that:
This “combining power” was afterwards called quantivalence or valency (and valence by American chemists).
of different chemical compound
s. In 1919, Irving Langmuir
, borrowed the term to explain Gilbert N. Lewis
's cubical atom
model by stating that "the number of pairs of electron
s which any given atom shares with the adjacent atoms is called the covalence of that atom." The prefix co- means "together", so that a co-valent bond means that the atoms share valence. Hence, if an atom, for example, had a +1 valence, meaning it has one valence electron beyond the complete shell, and another a −1 valence, meaning it requires one electron to complete its outer shell (missing an electron) , then a bond between these two atoms would result because they would be complementing or sharing their out of balance valence tendencies. Subsequently, it is now more common to speak of covalent bond
s rather than "valence", which has fallen out of use in higher level work with the advances in the theory of chemical bonding, but is still widely used in elementary studies where it provides a heuristic introduction to the subject.
, the valence can vary between one to seven, but usually these elements form a number of valence bonds between one and four. The number of bonds formed by a given element was originally thought to be a fixed chemical property. In fact, in most cases this is not true. For example, phosphorus
often has a valence of three, but can also have other valences.
Nevertheless, many elements have a common valence related to their position in the periodic table, following the octet rule
. Elements in the main groups 1
(alkali metals) and 17 (halogens) commonly have a valence of 1; elements in groups 2
(alkaline earth metals) and 16
(chalcogens) valence 2; elements in groups 13
(boron group) and 15
(nitrogen group) valence 3; elements in group 14
(carbon group) valence 4.
s as used in Stock nomenclature
for coordination compounds
, and the lambda notation, as used in the IUPAC nomenclature of inorganic chemistry
, "oxidation state
" is a more clear indication of the electronic state of atoms in a molecule.
The "oxidation state" of an atom in a molecule gives the number of valence electrons it has gained or lost.
In contrast to the valency number, the oxidation state can be positive (for an electropositive atom) or negative (for an electronegative
atom).
Elements in a high oxidation state can have a valence larger than four. For example, in perchlorate
s, chlorine has seven valence bonds and ruthenium
, in the +8 oxidation state in ruthenium(VIII) tetroxide
, has even eight valence bonds.
(IUPAC) has made several attempts to arrive at an unambiguous definition of valence. The current version, adopted in 1994,:
Hydrogen
and chlorine
were originally used as examples of univalent atoms, because of their nature to form only one single bond. Hydrogen has only one valence electron and can form only one bond with an atom that has an incomplete outer shell
. Chlorine has seven valence electrons and can form only one bond with an atom that donates a valence electron to complete chlorine's outer shell. However, chlorine can also have oxidation states from +1 to +7 and can form more than one bond by donating valence electrons.
Although hydrogen has only one valence electron, it can form bonds with more than one atom in hypervalent bonds
. In the bifluoride ion , for example, it forms a three-center four-electron bond
with two fluoride atoms:
Another example is the Three-center two-electron bond
in diborane
(B2H6).
* The univalent perchlorate ion (ClO4−) has valence 1.
** Iron oxide appears in a crystal structure
, so no typical molecule can be identified.
In ferrous oxide, Fe has oxidation number II, in ferric oxide, oxidation number III.
(H) and of fluorine
(F) are both one. Astatine
(At) is predicted to have valence of seven but is not known to have compounds with a valency above one.
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
, valence, also known as valency or valence number, is a measure of the number of bonds
Bond order
Bond order is the number of chemical bonds between a pair of atoms. For example, in diatomic nitrogen N≡N the bond order is 3, while in acetylene H−C≡C−H the bond order between the two carbon atoms is also 3, and the C−H bond order is 1. Bond order gives an indication to the stability of a bond....
formed by an atom of a given element. "Valence" can be defined as the number of valence bonds
Valence bond theory
In chemistry, valence bond theory is one of two basic theories, along with molecular orbital theory, that were developed to use the methods of quantum mechanics to explain chemical bonding. It focuses on how the atomic orbitals of the dissociated atoms combine to give individual chemical bonds...
a given atom has formed, or can form, with one or more other atoms. For most elements the number of bonds can vary. The IUPAC
International Union of Pure and Applied Chemistry
The International Union of Pure and Applied Chemistry is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Council for Science . The international headquarters of IUPAC is located in Zürich,...
definition limits valence to the maximum number of univalent atoms that may combine with the atom, that is the maximum number of valence bonds that is possible for the given element.
The valence of an element depends on the number of valence electron
Valence electron
In chemistry, valence electrons are the electrons of an atom that can participate in the formation of chemical bonds with other atoms. Valence electrons are the "own" electrons, present in the free neutral atom, that combine with valence electrons of other atoms to form chemical bonds. In a single...
s that may be involved in the forming of valence bonds. A univalent (monovalent) atom, ion or group has a valence of one and thus can form one covalent bond
Covalent bond
A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....
. A divalent
Divalent
In chemistry, a divalent ion or molecule has a valence of two and thus can form two bonds with other ions or molecules. An older term for divalent is bivalent....
molecular entity
Molecular entity
According to the IUPAC Gold Book a molecular entity is "any constitutionally or isotopically distinct atom, molecule, ion, ion pair, radical, radical ion, complex, conformer, etc., identifiable as a separately distinguishable entity"....
has a valence of two and can form two sigma bonds to two different atoms or one sigma bond
Sigma bond
In chemistry, sigma bonds are the strongest type of covalent chemical bond. They are formed by head-on overlapping between atomic orbitals. Sigma bonding is most clearly defined for diatomic molecules using the language and tools of symmetry groups. In this formal approach, a σ-bond is...
plus one pi bond
Pi bond
In chemistry, pi bonds are covalent chemical bonds where two lobes of one involved atomic orbital overlap two lobes of the other involved atomic orbital...
to a single atom.
Alkyl groups and hydroxyl
Hydroxyl
A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...
ions are univalent examples; oxo ligand
Oxo ligand
In coordination chemistry, an oxo ligand is an oxygen atom bound only to one or more metal centers. These ligands can exist as terminal or as bridging atom . Oxo ligands stabilize high oxidation states of a metal....
s are divalent.
Over the last century, the concept of valence evolved into a range of approaches for describing the chemical bond, including Lewis structure
Lewis structure
Lewis structures are diagrams that show the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule. A Lewis structure can be drawn for any covalently bonded molecule, as well as coordination compounds...
s (1916), valence bond theory
Valence bond theory
In chemistry, valence bond theory is one of two basic theories, along with molecular orbital theory, that were developed to use the methods of quantum mechanics to explain chemical bonding. It focuses on how the atomic orbitals of the dissociated atoms combine to give individual chemical bonds...
(1927), molecular orbital
Molecular orbital
In chemistry, a molecular orbital is a mathematical function describing the wave-like behavior of an electron in a molecule. This function can be used to calculate chemical and physical properties such as the probability of finding an electron in any specific region. The term "orbital" was first...
s (1928), valence shell electron pair repulsion theory
VSEPR theory
Valence shell electron pair repulsion theory is a model in chemistry used to predict the shape of individual molecules based upon the extent of electron-pair electrostatic repulsion. It is also named Gillespie–Nyholm theory after its two main developers...
(1958) and all the advanced methods of quantum chemistry
Quantum chemistry
Quantum chemistry is a branch of chemistry whose primary focus is the application of quantum mechanics in physical models and experiments of chemical systems...
.
| In cyclohexanonoxime Oxime An oxime is a chemical compound belonging to the imines, with the general formula R1R2C=NOH, where R1 is an organic side chain and R2 may be hydrogen, forming an aldoxime, or another organic group, forming a ketoxime. O-substituted oximes form a closely related family of compounds... (image left), the nitrogen Nitrogen Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere... atom has three valence bonds and by the first definition it has a valence of three. Nitrogen has five valence electron Valence electron In chemistry, valence electrons are the electrons of an atom that can participate in the formation of chemical bonds with other atoms. Valence electrons are the "own" electrons, present in the free neutral atom, that combine with valence electrons of other atoms to form chemical bonds. In a single... s and by IUPAC definition it has a valence of five, because it can form maximal five valence bonds, as in N-methyl-1-phenylmethanimine oxide http://www.molport.com/buy-chemicals/moleculelink/N-methyl-1-phenylmethanimine-oxide/289834. In cyclohexanonoxime, nitrogen has the oxidation state Oxidation state In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by... −1 and 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... −2. |
History
The etymologyEtymology
Etymology is the study of the history of words, their origins, and how their form and meaning have changed over time.For languages with a long written history, etymologists make use of texts in these languages and texts about the languages to gather knowledge about how words were used during...
of the word "valence" traces back to 1425, meaning "extract, preparation," from Latin valentia "strength, capacity," and the chemical meaning referring to the "combining power of an element" is recorded from 1884, from German Valenz.
William Higgins (chemist)
William Higgins , an Irish chemist, was one of the early proponents of atomic theory. Known mainly for his speculative ideas on chemical combination, William Higgins is popular for the insights his life offers into the emergence of chemistry as a career during the British industrial revolution...
published views on what he called combinations of "ultimate" particles, which foreshadowed the concept of valency bonds. If, for example, according to Higgins, the force between the ultimate particle of oxygen and the ultimate particle of nitrogen were 6, then the strength of the force would be divided accordingly, and similarly for the other combinations of ultimate particles (see illustration).
The exact inception, however, of the theory of chemical valencies can be traced to an 1852 paper by Edward Frankland
Edward Frankland
Sir Edward Frankland, KCB, FRS was a chemist, one of the foremost of his day. He was an expert in water quality and analysis, and originated the concept of combining power, or valence, in chemistry. He was also one of the originators of organometallic chemistry.-Biography:Edward Frankland was born...
, in which he combined the older theories of free radicals and “type theory” with thoughts on chemical affinity
Chemical affinity
In chemical physics and physical chemistry, chemical affinity is the electronic property by which dissimilar chemical species are capable of forming chemical compounds...
to show that certain elements have the tendency to combine with other elements to form compounds containing 3, i.e. in the three atom groups (e.g. NO3, NH3, NI3, etc.) or 5, i.e. in the five atom groups (e.g. NO5, NH4O, PO5, etc.), equivalents of the attached elements. It is in this manner, according to Frankland, that their affinities are best satisfied. Following these examples and postulates, Frankland declares how obvious it is that:
This “combining power” was afterwards called quantivalence or valency (and valence by American chemists).
Covalence
The concept of covalence was developed in the middle of the nineteenth century in an attempt to rationalize the formulaeChemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
of different chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
s. In 1919, Irving Langmuir
Irving Langmuir
Irving Langmuir was an American chemist and physicist. His most noted publication was the famous 1919 article "The Arrangement of Electrons in Atoms and Molecules" in which, building on Gilbert N. Lewis's cubical atom theory and Walther Kossel's chemical bonding theory, he outlined his...
, borrowed the term to explain Gilbert N. Lewis
Gilbert N. Lewis
Gilbert Newton Lewis was an American physical chemist known for the discovery of the covalent bond , his purification of heavy water, his reformulation of chemical thermodynamics in a mathematically rigorous manner accessible to ordinary chemists, his theory of Lewis acids and...
's cubical atom
Cubical atom
The cubical atom was an early atomic model in which electrons were positioned at the eight corners of a cube in a non-polar atom or molecule. This theory was developed in 1902 by Gilbert N. Lewis and published in 1916 in the famous article "The Atom and the Molecule" and used to account for the...
model by stating that "the number of pairs of electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s which any given atom shares with the adjacent atoms is called the covalence of that atom." The prefix co- means "together", so that a co-valent bond means that the atoms share valence. Hence, if an atom, for example, had a +1 valence, meaning it has one valence electron beyond the complete shell, and another a −1 valence, meaning it requires one electron to complete its outer shell (missing an electron) , then a bond between these two atoms would result because they would be complementing or sharing their out of balance valence tendencies. Subsequently, it is now more common to speak of covalent bond
Covalent bond
A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....
s rather than "valence", which has fallen out of use in higher level work with the advances in the theory of chemical bonding, but is still widely used in elementary studies where it provides a heuristic introduction to the subject.
Common valences
For elements in the main groups of the periodic tablePeriodic 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...
, the valence can vary between one to seven, but usually these elements form a number of valence bonds between one and four. The number of bonds formed by a given element was originally thought to be a fixed chemical property. In fact, in most cases this is not true. For example, 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...
often has a valence of three, but can also have other valences.
Nevertheless, many elements have a common valence related to their position in the periodic table, following the octet rule
Octet rule
The octet rule is a chemical rule of thumb that states that atoms of low The octet rule is a chemical rule of thumb that states that atoms of low The octet rule is a chemical rule of thumb that states that atoms of low (The octet rule is a chemical rule of thumb that states that atoms of low (...
. Elements in the main groups 1
Alkali metal
The alkali metals are a series of chemical elements in the periodic table. In the modern IUPAC nomenclature, the alkali metals comprise the group 1 elements, along with hydrogen. The alkali metals are lithium , sodium , potassium , rubidium , caesium , and francium...
(alkali metals) and 17 (halogens) commonly have a valence of 1; elements in groups 2
Alkaline earth metal
The alkaline earth metals are a group in the periodic table. In the modern IUPAC nomenclature, the alkaline earth metals are called the group 2 elements. Previously, they were called the Group IIA elements . The alkaline earth metals contain beryllium , magnesium , calcium , strontium , barium and...
(alkaline earth metals) and 16
Chalcogen
The chalcogens are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family...
(chalcogens) valence 2; elements in groups 13
Boron group
The boron group is the series of elements in group 13 of the periodic table, comprising boron , aluminium , gallium , indium , thallium , and ununtrium . The elements in the boron group are characterized by having three electrons in their outer energy levels...
(boron group) and 15
Nitrogen group
The nitrogen group is a periodic table group consisting of nitrogen , phosphorus , arsenic , antimony , bismuth and ununpentium ....
(nitrogen group) valence 3; elements in group 14
Carbon group
The carbon group is a periodic table group consisting of carbon , silicon , germanium , tin , lead , and ununquadium ....
(carbon group) valence 4.
Valence versus oxidation state
Because of the ambiguity of the term valence, nowadays other notations are used in practice. Beside the system of oxidation numberOxidation number
In coordination chemistry, the oxidation number of a central atom in a coordination compound is the charge that it would have if all the ligands were removed along with the electron pairs that were shared with the central atom. Oxidation numbers are often confused with oxidation states.The...
s as used in Stock nomenclature
Stock nomenclature
Stock nomenclature for inorganic compounds is a widely used system of chemical nomenclature developed by the German chemist Alfred Stock and first published in 1919...
for coordination compounds
, and the lambda notation, as used in the IUPAC nomenclature of inorganic chemistry
IUPAC nomenclature of inorganic chemistry
The IUPAC nomenclature of inorganic chemistry is a systematic method of naming inorganic chemical compounds, as recommended by the International Union of Pure and Applied Chemistry . The rules are commonly known as "The Red Book"...
, "oxidation state
Oxidation state
In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...
" is a more clear indication of the electronic state of atoms in a molecule.
The "oxidation state" of an atom in a molecule gives the number of valence electrons it has gained or lost.
In contrast to the valency number, the oxidation state can be positive (for an electropositive atom) or negative (for an electronegative
Electronegativity
Electronegativity, symbol χ , is a chemical property that describes the tendency of an atom or a functional group to attract electrons towards itself. An atom's electronegativity is affected by both its atomic number and the distance that its valence electrons reside from the charged nucleus...
atom).
Elements in a high oxidation state can have a valence larger than four. For example, in perchlorate
Perchlorate
Perchlorates are the salts derived from perchloric acid . They occur both naturally and through manufacturing. They have been used as a medicine for more than 50 years to treat thyroid gland disorders. They are used extensively within the pyrotechnics industry, and ammonium perchlorate is also a...
s, chlorine has seven valence bonds and ruthenium
Ruthenium
Ruthenium is a chemical element with symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most chemicals. The Russian scientist Karl Ernst Claus discovered the element...
, in the +8 oxidation state in ruthenium(VIII) tetroxide
Ruthenium tetroxide
Ruthenium tetroxide is a diamagnetic tetrahedral ruthenium compound. As expected for a charge-neutral symmetrical oxide, it is quite volatile. The analogous OsO4 is more widely used and better known...
, has even eight valence bonds.
"Maximum number of bonds" definition
The International Union of Pure and Applied ChemistryInternational Union of Pure and Applied Chemistry
The International Union of Pure and Applied Chemistry is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Council for Science . The international headquarters of IUPAC is located in Zürich,...
(IUPAC) has made several attempts to arrive at an unambiguous definition of valence. The current version, adopted in 1994,:
- The maximum number of univalent atoms (originally hydrogen or chlorine atoms) that may combine with an atom of the element under consideration, or with a fragment, or for which an atom of this element can be substituted.
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...
and 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...
were originally used as examples of univalent atoms, because of their nature to form only one single bond. Hydrogen has only one valence electron and can form only one bond with an atom that has an incomplete outer shell
Electron shell
An electron shell may be thought of as an orbit followed by electrons around an atom's nucleus. The closest shell to the nucleus is called the "1 shell" , followed by the "2 shell" , then the "3 shell" , and so on further and further from the nucleus. The shell letters K,L,M,.....
. Chlorine has seven valence electrons and can form only one bond with an atom that donates a valence electron to complete chlorine's outer shell. However, chlorine can also have oxidation states from +1 to +7 and can form more than one bond by donating valence electrons.
Although hydrogen has only one valence electron, it can form bonds with more than one atom in hypervalent bonds
Hypervalent molecule
A hypervalent molecule is a molecule that contains one or more main group elements formally bearing more than eight electrons in their valence shells...
. In the bifluoride ion , for example, it forms a three-center four-electron bond
Three-center four-electron bond
The 3-center 4-electron bond is a model used to explain bonding in hypervalent molecules such as phosphorus pentafluoride, sulfur hexafluoride, the xenon fluorides, and the bifluoride ion. It is also known as the Pimentel-Rundle three-center model after the work published by George C. Pimentel in...
with two fluoride atoms:
Another example is the Three-center two-electron bond
Three-center two-electron bond
A three-center two-electron bond is an electron-deficient chemical bond where three atoms share two electrons. The combination of three atomic orbitals form three molecular orbitals: one bonding, one non-bonding, and one anti-bonding. The two electrons go into the bonding orbital, resulting in a...
in diborane
Diborane
Diborane is the chemical compound consisting of boron and hydrogen with the formula B2H6. It is a colorless gas at room temperature with a repulsively sweet odor. Diborane mixes well with air, easily forming explosive mixtures. Diborane will ignite spontaneously in moist air at room temperature...
(B2H6).
Examples
(valencies according to the number of valence bonds definition and conform oxidation states)| COMPOUND | FORMULA | VALENCE | OXIDATION STATE |
|---|---|---|---|
| Hydrogen chloride Hydrogen chloride The compound hydrogen chloride has the formula HCl. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrogen chloride gas and hydrochloric acid are important in technology and industry... |
HCl | H=1 Cl=1 | H=+1 Cl=−1 |
| 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... |
Cl2 | Cl=1 Cl=1 | Cl=+1 Cl=−1 |
| Perchlorate Perchlorate Perchlorates are the salts derived from perchloric acid . They occur both naturally and through manufacturing. They have been used as a medicine for more than 50 years to treat thyroid gland disorders. They are used extensively within the pyrotechnics industry, and ammonium perchlorate is also a... * |
HClO4 | H=1 Cl=7 O=2 | H=+1 Cl=+7 O=−2 |
| Sodium hydride Sodium hydride Sodium hydride is the chemical compound with the empirical formula NaH. It is primarily used as a strong base in organic synthesis. NaH is representative of the saline hydrides, meaning it is a salt-like hydride, composed of Na+ and H− ions, in contrast to the more molecular hydrides such as... |
NaH | Na=1 H=1 | Na=+1 H=−1 |
| Ferrous oxide ** | FeO | Fe=2 O=2 | Fe=+2 O=−2 |
| Ferric oxide ** | Fe2O3 | Fe=3 O=2 | Fe=+3 O=−2 |
Crystal structure
In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...
, so no typical molecule can be identified.
In ferrous oxide, Fe has oxidation number II, in ferric oxide, oxidation number III.
Valences of the elements
Maximum valences for the majority of elements are based on the highest known fluoride. Note that valence of hydrogenHydrogen
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...
(H) and of fluorine
Fluorine
Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...
(F) are both one. Astatine
Astatine
Astatine is a radioactive chemical element with the symbol At and atomic number 85. It occurs on the Earth only as the result of decay of heavier elements, and decays away rapidly, so much less is known about this element than its upper neighbors in the periodic table...
(At) is predicted to have valence of seven but is not known to have compounds with a valency above one.