Question

What physical and chemical properties of elements were used by Mendeleev in creating his periodic table? List two observations which posed a challenge to Mendeleev's Periodic Law.

Answer 1

Physical and chemical properties used by Mendeleev in creating his periodic table:

1. Physical properties: Mendeleev arranged the periodic table in the increasing order of the atomic masses of the elements.

2. Chemical properties: Mendeleev distributed the elements into groups on the basis of formation of hydrides and oxides.

Challenges to Mendeleev's periodic law:

(i) Position of the isotopes: Isotopes have different masses, so they must be assigned separate positions in the periodic table.
(ii) Different groups of similar elements: Some chemically similar elements are placed in different groups, while some chemically different elements are placed in the same group.