When does covalent bonding occur?
Covalent bonding occurs when atoms share electrons. By sharing their outermost (valence) electrons, atoms can fill up their outer electron shells and gain stability by getting an octet of electrons. Nonmetals readily form covalent bonds with other nonmetals.
Only when two atoms of the same element form a covalent bond are the shared electrons actually shared equally (e.g.,
If the electronegativity difference between the two elements is very small (0.4 or less), the electrons are shared almost equally, and the bond is considered to be nonpolar covalent. If the electronegativity difference is between 0.4 and 1.7, the bond is polar covalent. If the electronegativity difference between the two elements is large (1.7 or greater), the bond is considered to be ionic.