At present, 118 elements are known to us. It is important to organise all the information we know about these elements. This forms the basis of periodic table.
Elements are classified on the basis of similarities in their properties. Dobereiner grouped the elements into triads and Newlands gave the Law of Octave, but it was Mendel who arranged the elements in increasing order of their atomic masses and according to their chemical properties. He made a table containing all elements and called it periodic table.
Anomalies in arrangement of elements based on increasing atomic mass could be removed when the elements were arranged in order of increasing atomic number, a fundamental property of the element discovered by Moseley. He made the Modern Periodic Table.
Elements in the Modern Periodic Table are arranged in 18 vertical columns called groups. and 7 horizontal rows called periods. Elements thus arranged show periodicity of properties including atomic size, valency or combining capacity and metallic and non-metallic character.
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