Dobereiner's Triads
Encyclopedia
Before the creation of the periodic table
by Mendeleev, there were several laws for the classification of the element
s. One of such laws was, Dobereiner's Law of Triad
s. Dobereiner between 1815 and 1829 gave his Law of Triads according to which in certain triads(groups of three elements) the atomic mass
of the central element was merely the arithmetic mean
of the atomic masses of the other two elements. But in certain triads all the three elements possessed nearly the same atomic masses, hence the law was rejected.
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...
by Mendeleev, there were several laws for the classification of the element
Element
- 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...
s. One of such laws was, Dobereiner's Law of Triad
Triad
Triad is a term used to describe many branches of Chinese criminal organizations based in Hong Kong, Vietnam, Macau, Taiwan, China, and also in countries with significant Chinese populations, such as Malaysia, Singapore, the United States, Canada, Australia and the United Kingdom...
s. Dobereiner between 1815 and 1829 gave his Law of Triads according to which in certain triads(groups of three elements) the atomic mass
Atomic mass
The atomic mass is the mass of a specific isotope, most often expressed in unified atomic mass units. The atomic mass is the total mass of protons, neutrons and electrons in a single atom....
of the central element was merely the arithmetic mean
Arithmetic mean
In mathematics and statistics, the arithmetic mean, often referred to as simply the mean or average when the context is clear, is a method to derive the central tendency of a sample space...
of the atomic masses of the other two elements. But in certain triads all the three elements possessed nearly the same atomic masses, hence the law was rejected.
| Element 1 Atomic mass |
Element 2 Atomic mass |
Element 3 Atomic mass |
Arithmetic mean |
|---|---|---|---|
Lithium Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly... 7.0 |
Sodium Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride... 23.0 |
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... 39.0 |
|
Calcium Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust... 40.0 |
Strontium Strontium is a chemical element with the symbol Sr and the atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically. The metal turns yellow when exposed to air. It occurs naturally in the minerals celestine and... 87.5 |
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... 137.0 |
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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... 35.0 |
Bromine Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826... 80.0 |
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.... 127.0 |
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Sulfur Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow... 32.0 |
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... 79.0 |
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