Concept explainers
Which substance in each of the following pairs would you expect to have the higher boiling point: (a) Ne or Xe, (b) CO2 or CS2, (c) CH4 or Cl2. (d) F2 or LiF, (e) NH3 or PH3? Explain why.
(a)

Interpretation:
The substance with higher boiling point in the given pairs of substances should be determined.
Concept introduction:
- Polarity of a bond is due to the difference in electro-negativities of atoms presented in it. The polarities of bonds are represented by using vectors.
- If the result of all bond polarities or vector sum is non-zero in a molecule, then the molecule is called as polar molecule.
- If the result of all bond polarities or vector sum is zero in a molecule, then the molecule is called as nonpolar molecule.
- Intermolecular force is the set of repulsive and attractive forces between molecules that result from the polarity between neighboring molecules. There are four types of intermolecular forces.
- Dipole – Dipole interaction: This force takes place between polar compounds.
- Hydrogen bonding is a type of dipole-dipole interaction of molecules when the hydrogen is bonded to strong electronegative atom (F, O, N, etc) in the molecules.
- Dispersion force is a weak force and this force is present in all compounds force.
- Boiling point is depending upon the strength of inter molecular forces.
Answer to Problem 7.37QP
Explanation of Solution
Therefore, only dispersion forces are presented in these molecules; dispersion forces is depends upon the molecular weight.
Boiling point is depending upon the strength of inter molecular forces.
Hence,
(b)

Interpretation:
The substance with higher boiling point in the given pairs of substances should be determined.
Concept introduction:
- Polarity of a bond is due to the difference in electro-negativities of atoms presented in it. The polarities of bonds are represented by using vectors.
- If the result of all bond polarities or vector sum is non-zero in a molecule, then the molecule is called as polar molecule.
- If the result of all bond polarities or vector sum is zero in a molecule, then the molecule is called as nonpolar molecule.
- Intermolecular force is the set of repulsive and attractive forces between molecules that result from the polarity between neighboring molecules. There are four types of intermolecular forces.
- Dipole – Dipole interaction: This force takes place between polar compounds.
- Hydrogen bonding is a type of dipole-dipole interaction of molecules when the hydrogen is bonded to strong electronegative atom (F, O, N, etc) in the molecules.
- Dispersion force is a weak force and this force is present in all compounds force.
- Boiling point is depending upon the strength of inter molecular forces.
Answer to Problem 7.37QP
Explanation of Solution
In
There are two C-S presented in
The result of all the bond polarities are the sum of all the vectors associated with each bonds.
The directions of C-S bond vectors are opposite to each other, so they cancel each other.
Hence,
The vector sum or the result of bond polarities for
Therefore,
Only dispersion forces are present in
In
There are two C-O presented in
The result of all the bond polarities are the sum of all the vectors associated with each bonds.
The directions of C-O bond vectors are opposite to each other, so they cancel each other.
Hence,
The vector sum or the result of bond polarities for
Therefore,
Only dispersion forces are present in
Dispersion forces is depends upon the molecular weight.
Boiling point depends upon the strength of inter molecular forces.
Hence,
(c)

Interpretation:
The substance with higher boiling point in the given pairs of substances should be determined.
Concept introduction:
- Polarity of a bond is due to the difference in electro-negativities of atoms presented in it. The polarities of bonds are represented by using vectors.
- If the result of all bond polarities or vector sum is non-zero in a molecule, then the molecule is called as polar molecule.
- If the result of all bond polarities or vector sum is zero in a molecule, then the molecule is called as nonpolar molecule.
- Intermolecular force is the set of repulsive and attractive forces between molecules that result from the polarity between neighboring molecules. There are four types of intermolecular forces.
- Dipole – Dipole interaction: This force takes place between polar compounds.
- Hydrogen bonding is a type of dipole-dipole interaction of molecules when the hydrogen is bonded to strong electronegative atom (F, O, N, etc) in the molecules.
- Dispersion force is a weak force and this force is present in all compounds force.
- Boiling point is depending upon the strength of inter molecular forces.
Answer to Problem 7.37QP
Explanation of Solution
The Cl-Cl bond in the
Therefore,
Only dispersion forces are present in
In
There are four C-H presented in
The result of all the bond polarities are the sum of all the vectors associated with each bonds.
The directions of C-H bond vectors are opposite to each other, so they cancel each other.
Hence,
The vector sum or the result of bond polarities for
Since the
Dispersion forces is depends upon the molecular weight.
Boiling point is depending upon the strength of inter molecular forces.
Hence,
(d)

Interpretation:
The substance with higher boiling point in the given pairs of substances should be determined.
Concept introduction:
- Polarity of a bond is due to the difference in electro-negativities of atoms presented in it. The polarities of bonds are represented by using vectors.
- If the result of all bond polarities or vector sum is non-zero in a molecule, then the molecule is called as polar molecule.
- If the result of all bond polarities or vector sum is zero in a molecule, then the molecule is called as nonpolar molecule.
- Intermolecular force is the set of repulsive and attractive forces between molecules that result from the polarity between neighboring molecules. There are four types of intermolecular forces.
- Dipole – Dipole interaction: This force takes place between polar compounds.
- Hydrogen bonding is a type of dipole-dipole interaction of molecules when the hydrogen is bonded to strong electronegative atom (F, O, N, etc) in the molecules.
- Dispersion force is a weak force and this force is present in all compounds force.
- Boiling point is depending upon the strength of inter molecular forces.
Answer to Problem 7.37QP
Explanation of Solution
The F-F bond in the
Therefore,
Only dispersion forces are present in
Therefore,
Ionic forces are present in
Since ionic forces stronger than dispersion forces, then
Boiling point depends upon the strength of inter molecular forces.
Hence,
(e)

Interpretation:
The substance with higher boiling point in the given pairs of substances should be determined.
Concept introduction:
- Polarity of a bond is due to the difference in electro-negativities of atoms presented in it. The polarities of bonds are represented by using vectors.
- If the result of all bond polarities or vector sum is non-zero in a molecule, then the molecule is called as polar molecule.
- If the result of all bond polarities or vector sum is zero in a molecule, then the molecule is called as nonpolar molecule.
- Intermolecular force is the set of repulsive and attractive forces between molecules that result from the polarity between neighboring molecules. There are four types of intermolecular forces.
- Dipole – Dipole interaction: This force takes place between polar compounds.
- Hydrogen bonding is a type of dipole-dipole interaction of molecules when the hydrogen is bonded to strong electronegative atom (F, O, N, etc) in the molecules.
- Dispersion force is a weak force and this force is present in all compounds force.
- Boiling point is depending upon the strength of inter molecular forces.
Answer to Problem 7.37QP
Explanation of Solution
In ammonia (
Three N-H bonds are presented and due to the difference in electronegativities of nitrogen and hydrogen, it has bond polarity. So
Polar molecules exhibit dipole-dipole interactions.
Since the hydrogen atom is bonded to nitrogen, then hydrogen bonding will be presented in between
In
Three P-H bonds are presented and due to the difference in electronegativities of phosphorus and hydrogen, it has bond polarity. So
Polar molecules exhibit dipole-dipole interactions.
Boiling point depends upon the strength of inter molecular forces.
Hence,
The molecules of higher boiling point in the given pairs of molecules are determined according to the polarities or molecular weights of molecules.
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Chapter 7 Solutions
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