Question
Explain the following:
(i) Boron is trivalent
(ii) Boron and aluminium tend to form covalent compounds.
Solution
(i) The electronic configuration of 5B is 1s2 2s2 2p1. Its tri valency is explained by promoting the electron from 2s to 2p so that number of unpaired electrons become three. One 2s and two 2p orbitals are hybridised to form a set of three equivalent sp2 hybrid orbitals which are triangular planar with a bond angle of 120°.
(ii) This is because they have small atomic sizes and hence higher ionisation energies due to which electrons can not be lost. Thus they also not form trivalent cations and their compounds are generally covalent in nature which is formed by the sharing of valence electrons with the valence electrons of the other atoms.
