Lanthanoids show limited number of oxidation state, viz., +2, +3 and +4 (out of which +3 is most common). This is because of large energy gap between 4f and 5d-subshells. The dominant oxidation state of actinoids is also +3 but they show a number of other oxidation states also. eg. uranium (Z = 92) and plutonium (Z = 94), show +3, +4, +5 and +6, neptunium (Z = 93) shows +3, +4, +5, +6 and +7 etc. This is due to small energy difference between 5f, 6d and 7s-subshells of the actinoids.
