Question

(a) State Mendeleev’s periodic law.

(b) What chemical properties of elements were used by Mendeleev in creating his periodic table ?

(c) State any three limitations of Mendeleev’s classification of elements.

(d) Besides gallium, which two other elements have since been discovered for which Mendeleev had left gaps in his periodic table ?

(e) Which group of elements was missing from Mendeleev’s original periodic table ?

Answer 1

(a) Mendeleev’s periodic law: The properties of elements are a periodic function of their atomic masses. It was the discovery of atomic number which led to a change in Mendeleev’s periodic law which was based on atomic mass.

(b) The elements having similar chemical properties form oxides and hydrides having similar formulae. Mendeleev used these properties for creating his periodic table.

(c) Limitations of Mendeleevs classification of elements:

(i) The position of isotopes could not be explained.

(ii) Wrong order of atomic masses of some elements could not be explained.

(iii) A correct position could not be assigned to Hydrogen in the periodic table.

(d) Silicon and Germanium.

(e) Noble gases were missing from Mendeleev’s original periodic table.