Arrange the following in the order of property indicated for each set:
(i) F2, Cl2, Br2, I2 - increasing bond dissociation enthalpy.
(ii) HF, HCl, HBr, HI - increasing acid strength.
(iii) NH3, PH3, AsH3, SbH3, BiH3 – increasing base strength.
1) As Bond dissociation energy generally decreases on moving down the group as the atomic size of the element increases. However, among halogens, the bond dissociation energy of F2 is lower than that of Cl2 and F2 due to the small atomic size of fluorine.
Thus increasing order for bond dissociation energy among halogens is as follows:
I2<F2<Br2<Cl2
2) As Bond dissociation energy of H-X molecules where X is the halogen decreases with increase in the atomic size. HI is the strongest acid as it loses H atom easily due to weak bonding between H and I.
So Increasing acid strength is as follows:
HF<HCl<HBr<HI
3) Basic strength decreases as we move from Nitrogen to Bismuth down the group as the size of the atom increases which is electron density of the atom decreases.
So Basic Strength is as follows:
BiH3<SbH3<AsH3<PH3<NH3