Chapter 14, Problem 14.80E

Interpretation Introduction

Interpretation:

An explanation as to how it would be determined whether ${\text{KrF}}_{\text{4}}$ had tetrahedral or square planar geometry is to be stated.

Concept Introduction:

A molecule having $N$ atoms uses $x$, $y$ and $z$ coordinates to describe the position of the each of the atoms. A molecule requires $3N$ coordinates to describe its position in space. For the change in position, the number of change in coordinates is the same, so $N$- molecule needs a total of $3N$ change in coordinates to describe its motion. The atoms are free to move in $3N$ different independent ways, so the molecule has $3N$ degree of freedom.

The number of vibrations or degree of freedom of linear molecule is $3N-5$, and the number of vibrations or degree of freedom of nonlinear molecule is $3N-6$. Only those vibrations which are involved in change in dipole moment are said to be IR-active vibrations.