how to calculate covalency?
Covalency is the property by which a bond is formed due the sharing of electrons between two atoms. It is usually formed between two non-metals. Thus covalency involves the sharing of electrons between the bonding atoms and not transfer of electrons.
For example, in CCl4, each chlorine atom shares one electron each with the carbon atom.
Covalency can be calculated from the number of electrons present in the valence shell. It is equal to the number of electrons required to complete the octet. For example, the number of valence electrons in carbon is 4, and hence it requires 4 electrons more to complete its octet. Therefore its covalency is 4. Similarly nitrogen has 5 electrons in its valence shell and requires 3 more to complete its octet. So its valency is 3.