Chapter 5.8, Problem 3QQ

Interpretation Introduction

Interpretation:

With three bonding groups and one nonbonding groups about the central atom, the molecular geometry that is associated has to be chosen from the given options.

Concept Introduction:

Information about the number of bonds and types of bonds can be obtained from Lewis structure but the molecular geometry cannot be obtained.  Three dimensional arrangement of atoms in a molecule can be given by molecular geometry.  Physical and chemical properties are determined by the molecular geometry of the molecule.

Using VSEPR theory and Lewis structure, the molecular geometry of the molecule that contain less number of atoms can be predicted.  VSEPR theory uses the information from Lewis structure of the molecule to predict the molecular geometry of the molecule.  Main concept of VSEPR theory is that electron pairs that are present in the valence shell adopt arrangement in a way that minimize the repulsion between like charges.

If the central atom contains two electron pairs, then it has to be far apart means, it has to be on opposite side of the nucleus.  This means the angle has to be $180°$ between them.  This type of arrangement for electron pair result in linear.

If the central atom contains three electron pairs, then it has to be far apart means, it has to be on corner of a triangle.  This means the angle has to be $120°$ between them.  This type of arrangement for electron pair result in trigonal planar.

If the central atom contains four electron pairs, then it has to be far apart means, it has to be in a tetrahedral arrangement.  This means the angle has to be $109°$ between them.  This type of arrangement for electron pair result in tetrahedral.

The collection of valence electron that is present in localized region about central atom in a molecule is known as VSEPR electron group.  This may contain two electrons, four electrons, or six electrons.  The electron group that contain four and six electrons repel each other.

Tetrahedral VSEPR electron group:

The four electron pairs can be of three VSEPR electron groups.  They are 4 bonding electron groups, 3 bonding and 1 nonbonding electron groups, and 2 bonding and 2 nonbonding electron groups.  The molecular geometry that is associated with 4 bonding electron groups is tetrahedral.  The molecular geometry that is associated with 3 bonding and 1 nonbonding electron groups is trigonal pyramidal.  The molecular geometry that is associated with 2 bonding and 2 nonbonding electron groups is angular.

Trigonal planar VSEPR electron group:

The three electron pairs can be of two VSEPR electron groups.  They are 3 bonding electron groups, and 2 bonding and 1 nonbonding electron groups.  The molecular geometry that is associated with 3 bonding electron groups is trigonal planar.  The molecular geometry that is associated with 2 bonding and 1 nonbonding electron groups is angular.

Linear VSEPR electron group:

The two electron pairs can be of only one VSEPR electron groups.  It is only 2 bonding electron groups and the geometry associated with it is linear geometry.