NEET Chemistry The p-Block Elements (XII) Questions Solved

BOARD

Account for the following:

(i) NH3 is a stronger base than PH3.

(ii) Sulphur has a greater tendency for catenation than oxygen.

(iii) Bond dissociation energy of F2 is less than that of Cl2.

(i) Since both P and N contain lone pairs of electrons but due to small size and high electronegativity of Nitrogen in NH3, the electron density is much higher than PH3, therefore it can easily donate electrons and acts as strong Lewis base than PH3.

(ii) The greater catenation tendency of sulphur is due to two reasons :

(a) The lone pair of electrons feels more repulsion in O-O bond than S-S bond due to its small size and thus S-S forms strong bond.

(b) As the size of atom increases down the group from O-PO, the strength of bond increases and therefore catenation tendency also increases.

(iii) Due to smaller size of F than Cl as a result of which electron-electron repulsions between the lone pairs of electrons are very large than that of Cl, hence bond dissociation energy of F2 is less than that of Cl2.

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