Answer:
When Mendeleev selected
his work, 63elements were known. He examined the relationship between the
atomic masses of the elements and their physical and chemical properties. Among
the chemical properties, he concentrated on the compounds formed by elements
with hydrogen and oxygen, He selected hydrogen and oxygen as they are very reactive
and formed compounds with most elements. The formulae of the hydrides and oxides
formed by elements were treated as one of the basic properties of the elements
for their classification.
He then took 63
cards and on each card he wrote down the properties of one element. He sorted
out the elements with similar properties and paired the cards together on a
wall. He observed that most of the elements get a place in a periodic table and
were arranged in order of their increasing atomic masses.
It was also observed
that there occurs aperiodic recurrence of elements with similar physical and
chemical properties. On this basis, Mendeleev formulated a periodic law, which
states that "the properties of elements are the periodic function of their
atomic masses".
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