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(i). Why does R3P=O exist but R3N=O does not? (ii). Why is NH3 more basic than PH3? (iii). Why sulphur is a polyatomic solid whereas oxygen is a diatomic gas |
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Answer» (i) Nitrogen does not contains d-orbitals. As a result, it cannot expand its covalency beyond four and cannot form pπ – dπ multiple bonds. In contrast, P contains the d-orbitals, and can expand its covalency beyond 4 and can form pπdπ multiple bonds. Hence R3P = O exist but R3N = O does not. (ii) Due to smaller atomic size the density of lone pair electrons on N in NH3 is larger than that of P in PH3. So, NH3 is a stronger Lewis base than that of PH3. (iii) The intermolecular forces in oxygen are weak van der Waals forces, which causes it to exist as gas. On the other hand, sulphur does not form strong S=S double bonds hence exists as a puckered structure held together by strong covalent bonds and exists as a polyatomic molecule. So, it exists as a solid. |
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