The p-Block Elements

The p-Block Elements

Question

Give reasons for the following:
(i) (CH3)3P = O exists but (CH3)3N = O does not.
(ii) Oxygen has less electron gain enthalpy with the negative sign than sulphur.
(iii) H3PO2 is a stronger reducing agent than H3PO3.

Answer

(i) N atom cannot expand its covalency beyond four due to the absence of vacant d- orbitals, whereas P atom possesses vacant d- orbitals. As a result, (CH3)3P = O exists but (CH3)3N = O does not.
(ii) Due to the small size and compact nature of the oxygen atom, the incoming electron is not accommodated with ease. As a result, oxygen has less electron gain enthalpy with a negative sign than sulphur.
(iii) Greater the number of element−hydrogen (E−H) bonds present in a compound, greater is the reducing nature of the compound. H3PO2 has two P−H bonds while H3PO3 has one P−H bond. Thus, H3PO2 is a stronger reducing agent than H3PO3.

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