Question

calculate the number of normal modes of vibration of brf5 and xef2

Answer 1

Question #61796, Chemistry, Other

Calculate the number of normal modes of vibration of BrF₅ and XeF₂.

Answer:

BrF₅

[3n₁-5] + [3n₂-6]

3n-5 is the formula for number of modes of vibration in linear molecule

3n-6 is the formula for number of modes of vibration in non-linear

combined both because the given molecule is complex (BrF₅)

where n = no. of electrons

where n₁ = no of electrons in linear (i.e., F & Lonepair in axial)

where n₂ = no of electrons in non-linear {4 F's in sq.plane}

F has 6e's

=> 3·(2+6)·5 + 3·(4·6)·6 = 3·8+3·24-11 = 24+72-11 = 85

Modes of Vibration in BrF₅ = 85

XeF₂ {also a complex} trigonal bipyramidal shape

lone pairs occupying a triangular plane

F's in axial because they're more EN than Lone Pair

=> 3·(2·6)·5 + 3·(3·2)·6 = 3·12+3·6-11 = 36+18-11 = 63

Modes of Vibration in XeF₂ = 63

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