Anomalous Behavior of Oxygen:- Like the usual trend of P-block elements, oxygen, the first member of gp. 16 differ from rest of the members of this group. The anomalous behavior of oxygen is due to the following properties:-

(i)          Small size.

(ii)         High electronegativity.

(iii)        Non-availability of d-orbitals in the valency shell.

Points of difference

(i)          Oxygen is a diatomic gas while others are complex solids.

(ii)         Oxygen is highly non-metallic due to high value of electronegativity.

(iii)        Oxygen is O2-ion very easily; the di-negative anions of other members are less common.

(iv)       Oxygen exhibits an oxidation state of -2 only except in OF2 where it has +2 state and peroxides where it has         1 state whereas rest all members show +4 and +6 oxidation states in addition to +2 oxidation state.

(v)         Oxygen molecule is highly stable because the two atoms are held together by fairly strong multiple bond having bond energy quite high. Thus ordinary oxygen is not active under ordinary conditions.

(vi)       Oxygen molecule is paramagnetic in nature in gaseous, liquid and solid states and has two unpaired electrons. Rest all are diamagnetic.

(vii)      Hydrogen bonding is present in water and may other compounds of oxygen due to high electronegativity of oxygen.

(viii)     Oxygen is the most abundant element on this planet.

(ix)       Oxygen is capable of forming P?-P? bonds with other elements of smaller size like carbon, nitrogen etc. the other members of this group do not show the tendency to exhibit such multiple bonding.