First member of each group of representative elements (i.e., s and p-block elements) shows anomalous behaviour due to the following reasons:

• Due to small atomic size

• D-orbitals are absent.

• Ionisation enthalpy

• Electron gain enthalpy

Li is a first group element. It has different properties and forms covalent compounds and nitrides.

Beryllium is first element of second group. It has various anomalies like it forms a covalent compound with coordination number four unlike other elements that have a coordination number 6.