Question

42. The geometry with respect to the central atom of the molecules, N(SiH3)3, N(CH3)3 and P(SiH3)3 are
1) Planar trigonal, trigonal pyramidal, trigonal pyramidal
2) Planar trigonal, trigonal pyramidal, trigonal planar
3) Trigonal pyramidal, trigonal pyramidal, trigonal planar
4) Trigonal planar, trigonal planar, trigonal pyramidal
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Answer 1

Answer:

(1) Planar, pyramidal, pyramidal

Explanation:

In molecule N(SiH₃)₃ hybridisation of N is sp² because the lone pair of N is in backbonding with vacant d-orbital of Si called pπ-dπ bonding. Hence its structure is trigonal planar.

Whereas in N(CH₃)₃ there is no vacant d-orbital hence no backbonding. Here hybridisation of N is sp³, which means trigonal pyramidal shape.

In case of P(SiH₃)₃ back bonding is not possible because P could not participate in pπ-dπ bonding. Hence hybridisation of P is sp³, which means trigonal pyramidal shape.