Chapter 9, Problem 1PE

Practice Exercise 9.1

Label the shapes of the following molecules:

Interpretation Introduction

Interpretation:

The molecular shapes of the given compounds are to be determined.

Concept Introduction:

Molecular shape is the three-dimensional arrangement of atoms that form a molecule. The molecular shape of any molecule is known as the geometry of that molecule.

The shape of a molecule is largely based on the five basic geometrical arrangements namely, linear, tetrahedral, octahedral, planar triangular, and trigonal bipyramidal.

Answer to Problem 1PE

Solution:

a) Tetrahedral

b) Trigonal bipyramidal

Explanation of Solution

a) Carbon tetrabromide

A molecule in which atoms are arranged in a four-sided geometric shape, with the formation of a pyramid-like structure, is said to be a tetrahedral molecule. This kind of arrangement occurs in the molecules that consist of five atoms in such a way that four atoms are linked with a central atom and all the four atoms have the same bond angle of ${109.5}^{°}$. The given molecule, carbon tetrabromide satisfies all these conditions.

Hence, ${\text{CBr}}_4$ is a tetrahedral molecule.

b) Arsenic pentafluoride

A molecule in which atoms are arranged in two triangular pyramidal planes is said to be a trigonal bipyramidal molecule. This kind of arrangement occurs in a molecule that consists of six atoms, such that three atoms are attached to a central atom with a bond angle of ${120}^{°}$, forming equatorial bonds and exhibiting pyramid shape in one plane. The other two atoms are also linked with the central atom but in a plane vertical to the equatorial plane, forming axial bonds with a bond angle of 90^o each. The given molecule arsenic pentafluoride satisfies all these conditions.

Hence, ${\text{AsF}}_5$ is a trigonal bipyramidal molecule.