Covalent Bonding: This is when pairs of electrons are shared by atoms, which is what valence bond theory primarily explains.
Sigma Bonds (ฯ): These are covalent bonds formed from direct overlap between atomic orbitals leading to electron sharing on the same axis as the bond.
Pi Bonds (ฯ): These are covalent bonds formed by sideways overlapping of atomic orbitals with electron sharing above and below the bond axis.