how we estimate covalencies of an atom?explain the covalency of boron

Covalency is the number of electron pairs an atom can share with other atoms. The total number of orbitals available in the valence shell is known as covalency, whether the orbitals are completely filled or empty . For example, the electronic configuration of Boron (Atomic Number 5) is 1s2 2s2 2p1. So, there are only two shells. The second shell contains one 2s orbitals and three 2p orbitals resulting total four orbitals in second shell. Therefore, Boron is restricted to a maximum covalency of 4 since only four(one s and three p) orbitals are available for bonding. Thanks & Regards Akshay Meena, askIITians Faculty M.Tech, IIT Kharagpur