Chapter 5, Problem 5.58EP

Specify both the VSEPR electron group geometry about the central atom and the molecular geometry for each of the following molecules or polyatomic ions.

1. a. CH₄
2. b. PH₄⁺
3. c. PH₃
4. d. NO₃⁻

Interpretation Introduction

Interpretation:

Electron group geometry and Molecular geometry about the central atom for ${\text{CH}}_{\text{4}}$ has to be predicted using VSEPR theory.

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.

Molecules with more than one central atom:

If a molecule contains more than one central atom then the molecular geometry for each central atom is given separately following the same rules applied for the molecules that contain one central atom.

Rules for predicting Geometry of molecules:

• Lewis structure for the given molecule has to be drawn.
• The number of VSEPR electron groups present about the central atom has to be counted in Lewis structure.
• Geometry has to be assigned considering minimum repulsion between the electron groups.

Answer to Problem 5.58EP

Electron group geometry is tetrahedral and molecular geometry about the central atom in ${\text{CH}}_{\text{4}}$ is tetrahedral.

Explanation of Solution

Given molecule is ${\text{CH}}_{\text{4}}$.  The Lewis structure for ${\text{CH}}_{\text{4}}$ can be drawn as shown below,

The above drawn structure for ${\text{CH}}_{\text{4}}$ contains only one central atom.  The central atom is a carbon atom.  The central carbon atom has four bonding electron groups and zero nonbonding electron groups.  The arrangement around this central carbon atom is tetrahedral arrangement.  Looking for molecular geometry, this central carbon atom contains four bonding electron groups and zero nonbonding electron groups and it has tetrahedral geometry as per VSEPR theory.

The electron group geometry and molecular geometry about the central atom is tetrahedral.

Conclusion

Electron group geometry and molecular geometry is predicted for ${\text{CH}}_{\text{4}}$ using VSEPR theory.

Interpretation Introduction

Interpretation:

Electron group geometry and Molecular geometry about the central atom for ${\text{PH}}_{\text{4}}{}^{+}$ has to be predicted using VSEPR theory.

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.

Molecules with more than one central atom:

If a molecule contains more than one central atom then the molecular geometry for each central atom is given separately following the same rules applied for the molecules that contain one central atom.

Rules for predicting Geometry of molecules:

• Lewis structure for the given molecule has to be drawn.
• The number of VSEPR electron groups present about the central atom has to be counted in Lewis structure.
• Geometry has to be assigned considering minimum repulsion between the electron groups.

Answer to Problem 5.58EP

Electron group geometry is tetrahedral and molecular geometry about the central atom in ${\text{PH}}_{\text{4}}{}^{+}$ is angular.

Explanation of Solution

Given molecule is ${\text{PH}}_{\text{4}}{}^{+}$.  The Lewis structure for ${\text{PH}}_{\text{4}}{}^{+}$ can be drawn as shown below,

The above drawn structure for ${\text{PH}}_{\text{4}}{}^{+}$ contains only one central atom.  The central atom is a phosphorus atom.  The central phosphorus atom has four bonding electron groups and zero nonbonding electron groups.  The arrangement around this central phosphorus atom is tetrahedral arrangement.  Looking for molecular geometry, this central phosphorus atom contains four bonding electron groups and zero nonbonding electron groups and it has tetrahedral geometry as per VSEPR theory.

The electron group geometry is tetrahedral and molecular geometry about the central atom is tetrahedral.

Conclusion

Electron group geometry and molecular geometry is predicted for ${\text{PH}}_{\text{4}}{}^{+}$ using VSEPR theory.

Interpretation Introduction

Interpretation:

Electron group geometry and Molecular geometry about the central atom for ${\text{PH}}_{\text{3}}$ has to be predicted using VSEPR theory.

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.

Molecules with more than one central atom:

If a molecule contains more than one central atom then the molecular geometry for each central atom is given separately following the same rules applied for the molecules that contain one central atom.

Rules for predicting Geometry of molecules:

• Lewis structure for the given molecule has to be drawn.
• The number of VSEPR electron groups present about the central atom has to be counted in Lewis structure.
• Geometry has to be assigned considering minimum repulsion between the electron groups.

Answer to Problem 5.58EP

Electron group geometry is tetrahedral and molecular geometry about the central atom in ${\text{PH}}_{\text{3}}$ is trigonal pyramidal.

Explanation of Solution

Given molecule is ${\text{PH}}_{\text{3}}$.  The Lewis structure for ${\text{PH}}_{\text{3}}$ can be drawn as shown below,

The above drawn structure for ${\text{PH}}_{\text{3}}$ contains only one central atom.  The central atom is a phosphorus atom.  The central phosphorus atom has three bonding electron groups and one nonbonding electron groups.  The arrangement around this central phosphorus atom is tetrahedral arrangement.  Looking for molecular geometry, this central phosphorus atom contains three bonding electron groups and one nonbonding electron groups and it has trigonal pyramidal geometry as per VSEPR theory.

The electron group geometry is tetrahedral and molecular geometry about the central atom is trigonal pyramidal.

Conclusion

Electron group geometry and molecular geometry is predicted for ${\text{PH}}_{\text{3}}$ using VSEPR theory.

Interpretation Introduction

Interpretation:

Electron group geometry and Molecular geometry about the central atom for ${\text{NO}}_{\text{3}}{}^{\text{-}}$ has to be predicted using VSEPR theory.

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.

Molecules with more than one central atom:

If a molecule contains more than one central atom then the molecular geometry for each central atom is given separately following the same rules applied for the molecules that contain one central atom.

Rules for predicting Geometry of molecules:

• Lewis structure for the given molecule has to be drawn.
• The number of VSEPR electron groups present about the central atom has to be counted in Lewis structure.
• Geometry has to be assigned considering minimum repulsion between the electron groups.

Answer to Problem 5.58EP

Electron group geometry is trigonal planar and molecular geometry about the central atom in ${\text{NO}}_{\text{3}}{}^{\text{-}}$ is trigonal planar.

Explanation of Solution

Given molecule is ${\text{NO}}_{\text{3}}{}^{\text{-}}$.  The Lewis structure for ${\text{NO}}_{\text{3}}{}^{\text{-}}$ can be drawn as shown below,

The above drawn structure for ${\text{NO}}_{\text{3}}{}^{\text{-}}$ contains only one central atom.  The central atom is a nitrogen atom.  The central nitrogen atom has three bonding electron groups and zero nonbonding electron groups.  The arrangement around this central nitrogen atom is trigonal planar arrangement.  Looking for molecular geometry, this central nitrogen atom contains three bonding electron groups and zero nonbonding electron groups and it has trigonal planar geometry as per VSEPR theory.

The electron group geometry is trigonal planar and molecular geometry about the central atom is trigonal planar.

Conclusion

Electron group geometry and molecular geometry is predicted for ${\text{NO}}_{\text{3}}{}^{\text{-}}$ using VSEPR theory.