(i) Catenation:- It is the linkage of atoms of the same element into longer chains. Catenation occurs most readily in carbon, which forms covalent bonds with other carbon atoms to form longer chains and structures. This property is due to strong C-C bonds.
(ii) Inert Pair Effect:- The reluctance of s electrons in participating in chemical bonding. It is due to the poor shillding of d and f block electrons of inner shell which increases the effective nuclear charge.
The term ‘inert pair’ was first proposed by N. Sidgwick in 1927. The name suggests that the s electrons are more tightly bound to the nucleus and therefore more difficult to ionize.
For example, the p-block elements of the 4th, 5th and 6th period come after d-block elements but the electrons present in the intervening d- (and f-) orbitals do not effectively shield the s-electrons of the valence shell. Due to this, the inert pair of ns electrons remains more tightly held by the nucleus and therefore participates less in bonding.
(iii) Allotropy:- Allotropy is the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of these elements. Allotropes are different structural modifications of an element, the atoms of the elements are bonded together in a different manner.
For example, the allotropes of carbon include diamond, graphite and fullerenes.