Chapter 10, Problem 10.94P

(a)

Interpretation Introduction

Interpretation:

The Lewis structure for ${\text{C}}_2{\text{H}}_4$ and ${\text{C}}_2{\text{F}}_4$ is to be drawn and also the ideal angle of $\text{H}-\text{C}-\text{H}$ and $\text{F}-\text{C}-\text{F}$ is to be determined.

Concept introduction:

The steps to draw the Lewis structure of the molecule are as follows:

Step 1: Find the central atom and place the other atoms around it. The atom in a compound which has the lowest group number or lowest electronegativity considered as the central atom.

Step 2: Calculate the total number of valence electrons.

Step 3: Connect the other atoms around the central atoms to the central atom with a single bond and lower the value of valence electrons by 2 of every single bond.

Step 4: Allocate the remaining electrons in pairs so that each atom can get 8 electrons.

(b)

Interpretation Introduction

Interpretation:

The deviations in $\text{H}-\text{C}-\text{H}$ and $\text{F}-\text{C}-\text{F}$ bond angles in the given molecules are to be explained.

Concept introduction:

VSEPR theory is based on the repulsions between the electrons pair in the valence shell. According to VSEPR theory, the shape of a molecule depends on the position of the electron pairs to minimize the repulsion, and maximize the stability.

According to VSEPR theory, the table for molecular geometries when the central atom has no lone pair is as follows:

$\begin{array}{ccc}\text{Electron}\text{groups}& \text{Geometry}& \text{Ideal bond angle}\\ 2& \text{Linear}& 180°\\ 3& \text{Trigonal}\text{Planar}& 120°\\ 4& \text{Tetrahedral}& 109.5°\\ 5& \text{Trigonal}\text{bipyramidal}& 90°,120°\\ 6& \text{Octahedral}& 90°\end{array}$