General electronic configuration of the groups are: ns 2 np 3,ns 2 np 4, ns 2 np 5, ns 2 np 6.

Radii increase down the group, however down the group the increse is small due to filling of electrons in d and f shells. The value of ionisation enthalpy decreases down the group due to increase in size. Electron gain enthalpy is the tendency of an element to accept electron. Study of this property in group 17 is more important. These elements Have the strong tendency to accept one electron and complete their octet. However the values of F are more – ve than that for Cl. This is due to the smaller size and strong repulsive force existing in F as compared to Cl.

The property of the element to form bonds with itself, hence exiting as a chain is called catenation. The first element of the groups having smaller size however have the tendency to form multiple bonds with itself and thus exist as discrete molecule. Catenation tendency increases down the group. Eg. N 2 vs P 4

Stability - NH 3 >PH 3 >AsH 3 >SbH 3 >BiH 3. Bond dissociation enthalpy - NH 3 >PH 3 >AsH 3 >SbH 3 >BiH 3 Reducing character - NH 3 <PH 3 <AsH 3 <SbH 3 <BiH 3 Basic character - NH 3 >PH 3 >AsH 3 >SbH 3 >BiH 3. Acidic character - N 2 O 3 > P 2 O 3 > As 2 O 3 > Sb 2 O 3 > Bi 2 O 3

Acidic character - H 2 O < H 2 S < H 2 Se < H 2 Te Thermal stability - H 2 O > H 2 S > H 2 Se >H 2 Te Reducing character - H 2 S < H 2 Se < H 2 Te Boiling point - H 2 S < H 2 Se < H 2 Te < H 2 O Reducing property of dioxides – SO 2 > SeO 2 > TeO 2

Stability of halides - F-> Cl-> Br- > I – Oxidising property – F 2 > Cl 2 >Br 2 > I 2 Acidic strength – HF< HCl< HBr< HI Stability & bond dissociation enthalpy - HF> HCl> HBr> HI Stability of oxides of halogens – I > Cl > Br Ionic character of halides – MF > MCl> MBr> MI