Chapter 3, Problem 3.26E

(a)

Interpretation Introduction

Interpretation:

Lewis structure of ${\text{PF}}_3$ has to be drawn. Shape of ${\text{PF}}_3$ has to be identified. Also, whether it can participate in dipole-dipole interactions or not has to be determined.

Concept Introduction:

Lewis structure represents covalent bonds and describes valence electrons configuration of atoms. The covalent bonds are depicted by lines and unshared electron pairs by pairs of dots. The sequence to write Lewis structure of some molecule is given as follows:

• The central atom is identified and various other atoms are arranged around it. This central atom so chosen is often the least electronegative.
• Total valence electrons are estimated for each atom.
• single bond is first placed between each atom pair.
• The electrons left can be allocated as unshared electron pairs or as multiple bonds around symbol of element to satisfy the octet (or duplet) for each atom.
• Add charge on overall structure in case of polyatomic cation or anion.

Hybridization is calculated by the hybrid orbitals and to calculate hybrid orbitals we need to know the steric number that is given by,

  $\text{Steric number}=\left[\begin{array}{c}\left(\text{number of atoms bonded to the central atom}\right)+\\ \left(\text{number of lone pairs on the central atom}\right)\end{array}\right]$        (1)

The relation of steric number with geometry or shape is depicted in the table below.

$\begin{array}{cccc}\text{Steric Number}& \text{Number of lone pairs}& \text{Molecular Geometry}& \text{Shape}\\ 2& 0& \text{linear}& \text{linear}\\ 3& \begin{array}{c}0\\ 1\end{array}& \begin{array}{c}\text{trigonal planar}\\ \text{trigonal planar}\end{array}& \begin{array}{c}\text{trigonal planar}\\ \text{bent}\end{array}\\ 4& \begin{array}{c}0\\ 1\\ 2\end{array}& \begin{array}{c}\text{tetrahedral}\\ \text{tetrahedral}\\ \text{tetrahedral}\end{array}& \begin{array}{c}\text{tetrahedral}\\ \text{trigonal pyramidal}\\ \text{bent}\end{array}\\ 5& \begin{array}{c}0\\ 1\\ 2\\ 3\end{array}& \begin{array}{c}\text{trigonal bipyramidal}\\ \text{trigonal bipyramidal}\\ \text{trigonal bipyramidal}\\ \text{trigonal bipyramidal}\end{array}& \begin{array}{c}\text{trigonal bipyramidal}\\ \text{see-saw}\\ \text{T-shaped}\\ \text{linear}\end{array}\\ 6& \begin{array}{c}0\\ 1\\ 2\end{array}& \begin{array}{c}\text{octahedral}\\ \text{octahedral}\\ \text{octahedral}\end{array}& \begin{array}{c}\text{octahedral}\\ \text{square pyramidal}\\ \text{square planar}\end{array}\end{array}$

(b)

Interpretation Introduction

Interpretation:

Lewis structure of ${\text{PF}}_5$ has to be drawn. Shape of ${\text{PF}}_5$ has to be identified. Also, whether it can participate in dipole-dipole interactions or not has to be determined.

Concept Introduction:

Refer to part (a).