Classification of Elements and Periodicity in Properties

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A periodic table is an arrangement of all the known elements, based on periodic law, in a manner that elements with similar properties fall in the same vertical column called a group.

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The physical and chemical properties of the elements (as well as the formulae and properties of their compounds) are the periodic functions of their atomic weights (atomic masses).

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Mendeleev classified elements on the basis of their atomic weights and periodicity in physical and chemical properties.

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Dobereiner arranged elements in groups of three called triads in such a way that the middle element had an atomic weight almost equal to the average of the other two, and the three elements showed sim…

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In the triad Li, Na, K, the atomic weight of sodium is 23, which is exactly equal to the average of Li and K: (7 + 39) / 2 = 23.

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If the elements are arranged in increasing order of their atomic weights, the properties of every eighth element are similar to those of the first one.

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It failed for elements of higher atomic weights, and the discovery of inert gases also gave a setback because they were quite different from other known elements and did not obey the law.

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He showed that properties such as atomic volume, density, melting point, boiling point, and thermal conductivity varied in a periodic fashion when plotted against atomic weights.