(a) Inert pair effect

As down group, s-block electrons participation in chemical bonding has been decreases. This phenomenon is known as ion pair effect. An element In group 13, has electronic configuration ns2 np1 and their valency is +3. While down the group, the +1 oxidation state becomes more stable. This is because of poor shielding of the ns2 electrons by d and f electrons. As a result, ns2 electrons are found tightly associated to the nucleus. Therefore, they can not participate in chemical bonding.

(b) allotropy

When an element exists with more than one form and consists with same chemical properties but different physical properties. This various forms of an element are known as allotropes. Example: carbon exist in three allotropic forms, are diamond, graphite and fullerenes.

(c) catenation

An atom of some element forms a linkage through strong covalent bonds to form long chains or branches. It is known as catenation. Example : carbon, sulphur, Silicon