Sulphur and rest of the elements of group 16 are less electronegative than oxygen. Therefore their atoms cannot take electrons easily. These elements exhibit -2 and +2 oxidation state in their compounds. In addition to this, they have vacant d-orbitals in their valency shell. To which electrons can be promoted from the $P$ and $S$ orbitals of the same shell as a result; they can show +4 and +6 oxidation state.