Question

state the periodic law in which mendeleev s periodic table was based .why was this periodic law changed ? name two elements whose properties were predicted on the basis of their position in mendeleevs periodic table.

Answer 1

Mendeleev’s periodic law: physical and chemical properties of elements are periodic property of their atomic mass.

Mendeleev’s periodic table was changed as it had some demerits, these are:
Position of hydrogen is confusing.
Some elements were not arranged according to their atomic mass. E.g I(atomic mass 126.92) was placed before Te (atomic mass 127.61).
Isotopes were kept together though they have different mass.
In 8^th group three elements were kept in single place.
Cu and Hg have similarity in their properties, though kept differently.

Mendeleev predicted properties of some element which were not discovered that time. These are Eka boron (Se), Eka aluminium (Ga), Eka silicon (Ge).