The number of electron pairs that an atom shares with one or more atoms of the same or different kind to achieve stable electronic configuration is called covalency. If an atom shares 1 electron, its covalency is equal to 1. If it can share 2 electrons, its covalency is 2.
The maximum valency for elements not having d orbital is equal to the number of unpaired electrons present in the valence shell of s and p orbital. The covalency is determined by the number of electrons shared while forming a chemical compound.
Maximum covalency of first elements of each group
The maximum covalency of the first elements of each group is 4. This is because of the following reasons:
- Small atomic size
- No vacant d orbitals
- Highly electronegative