Oxygen is the first member of the group 16 family and differs from the other members of the family because of

(1) Its small size

(2) Its high electronegativity

(3) Its high ionisation energy

(4) Absence of d-orbitals in the valence shell

It differs from the other members of the family as follows

(1) Elemental state : Oxygen is a diatomic gas while others are octa-atomic solids with eight membered puckered ring structure.

(2) Oxidation states : Oxygen shows O.S. of –2 in most of its compounds. It also shows an O. S. of +2 in F₂O and –1 in H₂O₂ or other peroxides. It cannot show O.S. beyond 2. Other elements show oxidation states of +2, +4 and +6 because these elements have vacant d-orbitals so that their valence shell can expand.

(3) Hydrogen-bonding : Oxygen atom is very small and has quite high nuclear charge. therefore, it has high value of electronegativity and is able to form H -bonds. the other elements, because of their large size, cannot form H -bonds. As a result, H₂O is liquid while H₂S is a gas and H₂Se etc., are solids.

(4) Maximum covalency : Oxygen has a maxium covalency of two while other elements can show a maximum covalency of six. This is because these elements have vacant d-orbitals while oxygen has not.

(5) Types of compounds : The compounds of oxygen are mainly ionic and polar covalent due to high electronegativity of oxygen while those of others are not.

(6) Magnetic character : Oxygen is paramagnetic while others are not.