Chapter 13, Problem 68E

Classify each of the following statements as true or false:

a) Molecular geometry around an atom may or may not be the same as electron-pair geometry around the atom.

b) Electron pair geometry is the direct effect of molecular geometry.

c) If the geometry of a molecule is linear, the molecule must have at least one double bond.

d) A molecule with a double bond cannot have trigonal pyramidal geometry around the double bonded atom.

e) A ${\text{CO}}_{\text{2}}$ molecule is linear, but an ${\text{SO}}_{\text{2}}$ molecule is bent.

f) A molecule is polar if it contains polar bonds.

g) A molecule with a central atom that has one lone pair of electrons is always polar.

h) A molecule with a central atom that has two lone pairs and two bonded pairs of electrons is always polar.

i) Carbon atoms normally form four bonds.

j) Hydrogen atoms never form double bonds.

Interpretation Introduction

(a)

Interpretation:

Whether the statement, “Molecular geometry around an atom may or may not be the same as electron-pair geometry around the atom” is true or false is to be stated.

Concept introduction:

Molecular geometry is the $\text{3}-\text{D}$ representation of the molecule in a space. As the Lewis model is not able to explain the shape of the molecules. In terms of electron density, the bonding electrons as well as lone pair of electrons predict the shape of the molecule.

Answer to Problem 68E

The statement, “Molecular geometry around an atom may or may not be the same as electron-pair geometry around the atom” is true.

Explanation of Solution

The electron-pair geometry of any molecule can be decided on the basis of the number of electron pairs present around the central atom. Some electron pairs around the central metal atom are bonded and some are present as lone pairs. The electron-pair geometry is decided without considering the lone pairs. The molecular geometry is decided by considering the lone pairs. Therefore, if there is no lone pair present around a central atom, then the molecular geometry around an atom may be the same as electron-pair geometry. If there is lone pair present around the central atom, then molecular geometry around an atom may not be the same as electron-pair geometry. Therefore, the statement, “Molecular geometry around an atom may or may not be the same as electron-pair geometry around the atom” is true.

Conclusion

The statement, “Molecular geometry around an atom may or may not be the same as electron-pair geometry around the atom” is found to be true.

Interpretation Introduction

(b)

Interpretation:

Whether the statement, “Electron pair geometry is the direct effect of molecular geometry” is true or false is to be stated.

Concept introduction:

Molecular geometry is the $\text{3}-\text{D}$ representation of the molecule in a space. As the Lewis model is not able to explain the shape of the molecules. In terms of electron density, the bonding electrons as well as lone pair of electrons predict the shape of the molecule.

Answer to Problem 68E

The statement, “Electron pair geometry is the direct effect of molecular geometry” is false.

Explanation of Solution

The electron-pair geometry is decided without considering the lone pairs. The molecular geometry is decided by considering both the lone pairs and the bond pairs. Therefore, electron pair geometry is not the direct effect of molecular geometry. Therefore, the statement, “Electron pair geometry is the direct effect of molecular geometry” is false.

Conclusion

The statement, “Electron pair geometry is the direct effect of molecular geometry” is found to be false.

Interpretation Introduction

(c)

Interpretation:

Whether the statement, “If the geometry of a molecule is linear, the molecule must have at least one double bond” is true or false is to be stated.

Concept introduction:

Molecular geometry is the $\text{3}-\text{D}$ representation of the molecule in a space. As the Lewis model is not able to explain the shape of the molecules. In terms of electron density, the bonding electrons as well as lone pair of electrons predict the shape of the molecule.

Answer to Problem 68E

The statement, “If the geometry of a molecule is linear, the molecule must have at least one double bond” is false.

Explanation of Solution

If the geometry of a molecule is linear, the molecule must have two bond pairs around the central metal atom. There is no condition to have a double bond for linear molecule. The double bond is considered as electron density cloud. Therefore, the statement, “If the geometry of a molecule is linear, the molecule must have at least one double bond” is false.

Conclusion

The statement, “If the geometry of a molecule is linear, the molecule must have at least one double bond” is found to be false.

Interpretation Introduction

(d)

Interpretation:

Whether the statement, “A molecule with a double bond cannot have trigonal pyramidal geometry around the double bonded atom” is true or false is to be stated.

Concept introduction:

Molecular geometry is the $\text{3}-\text{D}$ representation of the molecule in a space. As the Lewis model is not able to explain the shape of the molecules. In terms of electron density, the bonding electrons as well as lone pair of electrons predict the shape of the molecule.

Answer to Problem 68E

The statement, “A molecule with a double bond cannot have trigonal pyramidal geometry around the double bonded atom” is true.

Explanation of Solution

The trigonal pyramidal geometry is formed when a molecule have three bond pair and one lone pair. Ammonia $\left({\text{NH}}_{\text{3}}\right)$ has trigonal pyramidal geometry. Sulfite ion $\left({\text{SO}}_{\text{3}}{}^{2-}\right)$ with double bond has trigonal pyramidal geometry. The molecule with a double bond cannot have pyramidal geometry around the double bonded atom. Therefore, the statement, “A molecule with a double bond cannot have trigonal pyramidal geometry around the double bonded atom” is true.

Conclusion

The statement, “A molecule with a double bond cannot have trigonal pyramidal geometry around the double bonded atom” is found to be true.

Interpretation Introduction

(e)

Interpretation:

Whether the statement, “A ${\text{CO}}_{\text{2}}$ molecule is linear, but an ${\text{SO}}_{\text{2}}$ molecule is bent” is true or false is to be stated.

Concept introduction:

Molecular geometry is the $\text{3}-\text{D}$ representation of the molecule in a space. As the Lewis model is not able to explain the shape of the molecules. In terms of electron density, the bonding electrons as well as lone pair of electrons predict the shape of the molecule.

Answer to Problem 68E

The statement, “A ${\text{CO}}_{\text{2}}$ molecule is linear, but an ${\text{SO}}_{\text{2}}$ molecule is bent” is true.

Explanation of Solution

In ${\text{CO}}_{\text{2}}$ molecule, central atom has only two bond pairs. In ${\text{SO}}_{\text{2}}$ molecule, central metal atom has two bond pairs as well as one lone pair. Therefore, the presence of lone pair distorted the linear structure to bent structure. Therefore, the ${\text{CO}}_{\text{2}}$ molecule is linear, but an ${\text{SO}}_{\text{2}}$ molecule is bent. Therefore, the statement, “A ${\text{CO}}_{\text{2}}$ molecule is linear, but an ${\text{SO}}_{\text{2}}$ molecule is bent” is true.

Conclusion

The statement, “A ${\text{CO}}_{\text{2}}$ molecule is linear, but an ${\text{SO}}_{\text{2}}$ molecule is bent” is found to be true.

Interpretation Introduction

(f)

Interpretation:

Whether the statement, “A molecule is polar if it contains polar bonds” is true or false is to be stated.

Concept introduction:

Molecular geometry is the $\text{3}-\text{D}$ representation of the molecule in a space. As the Lewis model is not able to explain the shape of the molecules. In terms of electron density, the bonding electrons as well as lone pair of electrons predict the shape of the molecule.

Answer to Problem 68E

The statement, “A molecule is polar if it contains polar bonds” is false.

Explanation of Solution

Polar molecules are those molecules which have permanent dipole moment. Polarity depends on the symmetry of the molecule. In symmetric molecules, the net dipole moment is zero. This is because of cancellation of polar bonds in opposite directions. Therefore, symmetric molecules are nonpolar. Generally, asymmetric molecules are polar and symmetric molecules are nonpolar. Therefore, a molecule having polar bonds need not be polar. Therefore, the statement, “A molecule is polar if it contains polar bonds” is false.

Conclusion

The statement, “A molecule is polar if it contains polar bonds” is found to be false.

Interpretation Introduction

(g)

Interpretation:

Whether the statement, “A molecule with a central atom that has one lone pair of electrons is always polar” is true or false is to be stated.

Concept introduction:

Molecular geometry is the $\text{3}-\text{D}$ representation of the molecule in a space. As the Lewis model is not able to explain the shape of the molecules. In terms of electron density, the bonding electrons as well as lone pair of electrons predict the shape of the molecule.

Answer to Problem 68E

The statement, “A molecule with a central atom that has one lone pair of electrons is always polar” is true.

Explanation of Solution

The lone pair present on the central atom distorts the symmetry of the molecule Therefore, the molecule becomes asymmetric. Asymmetric molecules are polar. So, molecule having lone pair on the central atom is polar in nature. Therefore, the statement, “A molecule with a central atom that has one lone pair of electrons is always polar” is true.

Conclusion

The statement, “A molecule with a central atom that has one lone pair of electrons is always polar” is found to be true.

Interpretation Introduction

(h)

Interpretation:

Whether the statement, “A molecule with a central atom that has two lone pair and two bonded pair of electrons is always polar” is true or false is to be stated.

Concept introduction:

Molecular geometry is the $\text{3}-\text{D}$ representation of the molecule in a space. As the Lewis model is not able to explain the shape of the molecules. In terms of electron density, the bonding electrons as well as lone pair of electrons predict the shape of the molecule.

Answer to Problem 68E

The statement, “A molecule with a central atom that has two lone pair and two bonded pair of electrons is always polar” is true.

Explanation of Solution

The lone pair present on the central atom distorts the symmetry of the molecule Therefore, the molecule becomes asymmetric. Asymmetric molecules are polar. So, molecule having lone pair on the central atom is polar in nature. Therefore, the statement, “A molecule with a central atom that has two lone pair and two bonded pair of electrons is always polar” is true.

Conclusion

The statement, “A molecule with a central atom that has two lone pair and two bonded pair of electrons is always polar” is found to be true.

Interpretation Introduction

(i)

Interpretation:

Whether the statement, “Carbon atoms normally form four bonds” is true or false is to be stated.

Concept introduction:

Molecular geometry is the $\text{3}-\text{D}$ representation of the molecule in a space. As the Lewis model is not able to explain the shape of the molecules. In terms of electron density, the bonding electrons as well as lone pair of electrons predict the shape of the molecule.

Answer to Problem 68E

The statement, “Carbon atoms normally form four bonds” is true.

Explanation of Solution

The valency of carbon is four. Tetravalency of the carbon is an important feature to form four stable bonds. Tetravalent carbon atom forms four bonds with other atoms. Therefore, the statement, “Carbon atoms normally form four bonds” is true.

Conclusion

The statement, “Carbon atoms normally form four bonds” is found to be true.

Interpretation Introduction

(j)

Interpretation:

Whether the statement, “Hydrogen atoms never form double bonds” is true or false is to be stated.

Concept introduction:

Molecular geometry is the $\text{3}-\text{D}$ representation of the molecule in a space. As the Lewis model is not able to explain the shape of the molecules. In terms of electron density, the bonding electrons as well as lone pair of electrons predict the shape of the molecule.

Answer to Problem 68E

The statement, “Hydrogen atoms never form double bonds” is true.

Explanation of Solution

The atomic number of hydrogen atom is one. Therefore, it has only one valence electron. Therefore, it can form only one bond with other atom. Therefore, the statement, “Hydrogen atoms never form double bonds” is true.

Conclusion

The statement, “Hydrogen atoms never form double bonds” is found to be true.