(also, London dispersion force) attraction between two rapidly fluctuating, temporary dipoles; significant only when particles are very close together

occurs when exceptionally strong dipoles attract; bonding that exists when hydrogen is bonded to one of the three most electronegative elements: F, O, or N

temporary dipole formed when the electrons of an atom or molecule are distorted by the instantaneous dipole of a neighboring atom or molecule

temporary dipole that occurs for a brief moment in time when the electrons of an atom or molecule are distributed asymmetrically

noncovalent attractive force between atoms, molecules, and/or ions

measure of the ability of a charge to distort a molecule’s charge distribution (electron cloud)

attractive or repulsive force between molecules, including dipole-dipole, dipole-induced dipole, and London dispersion forces; does not include forces due to covalent or ionic bonding, or the attraction between ions and molecules

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Chemistry 2e · 10.1 Intermolecular Forces

Intermolecular Forces: practice problems

11 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

Exercises 1
In terms of their bulk properties, how do liquids and solids differ? How are they similar?
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Exercises 3
In terms of the kinetic molecular theory, in what ways are liquids similar to gases? In what ways are liquids different from gases?
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Exercises 5
What is the evidence that all neutral atoms and molecules exert attractive forces on each other?
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Exercises 7
Define the following and give an example of each:
(a) dispersion force
(b) dipole-dipole attraction
(c) hydrogen bond
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Exercises 9
Why do the boiling points of the noble gases increase in the order He < Ne < Ar < Kr < Xe?
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Exercises 11
Arrange each of the following sets of compounds in order of increasing boiling point temperature:
(a) HCl, H₂O, SiH₄
(b) F₂, Cl₂, Br₂
(c) CH₄, C₂H₆, C₃H₈
(d) O₂, NO, N₂
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Exercises 13
On the basis of intermolecular attractions, explain the differences in the boiling points of n–butane (−1 °C) and chloroethane (12 °C), which have similar molar masses.
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Exercises 15
The melting point of H₂O(s) is 0 °C. Would you expect the melting point of H₂S(s) to be −85 °C, 0 °C, or 185 °C? Explain your answer.
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Exercises 17
Explain why a hydrogen bond between two water molecules is weaker than a hydrogen bond between two hydrogen fluoride molecules.
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Exercises 19
Proteins are chains of amino acids that can form in a variety of arrangements, one of which is a helix. What kind of IMF is responsible for holding the protein strand in this shape? On the protein image, show the locations of the IMFs that hold the protein together:
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Exercises 21
Identify the intermolecular forces present in the following solids:
(a) CH₃CH₂OH
(b) CH₃CH₂CH₃
(c) CH₃CH₂Cl
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Key terms · 8

dipole-dipole attraction: intermolecular attraction between two permanent dipoles
dispersion force: (also, London dispersion force) attraction between two rapidly fluctuating, temporary dipoles; significant only when particles are very close together
hydrogen bonding: occurs when exceptionally strong dipoles attract; bonding that exists when hydrogen is bonded to one of the three most electronegative elements: F, O, or N
induced dipole: temporary dipole formed when the electrons of an atom or molecule are distorted by the instantaneous dipole of a neighboring atom or molecule
instantaneous dipole: temporary dipole that occurs for a brief moment in time when the electrons of an atom or molecule are distributed asymmetrically
intermolecular force: noncovalent attractive force between atoms, molecules, and/or ions
polarizability: measure of the ability of a charge to distort a molecule’s charge distribution (electron cloud)
van der Waals force: attractive or repulsive force between molecules, including dipole-dipole, dipole-induced dipole, and London dispersion forces; does not include forces due to covalent or ionic bonding, or the attraction between ions and molecules

Learn 10.1 on the whiteboard

The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.

Read 10.1 in the textbook · This section on openstax.org

Intermolecular Forces: practice problems

11 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

Exercises 1

In terms of their bulk properties, how do liquids and solids differ? How are they similar?

Exercises 3

In terms of the kinetic molecular theory, in what ways are liquids similar to gases? In what ways are liquids different from gases?

Exercises 5

What is the evidence that all neutral atoms and molecules exert attractive forces on each other?

Exercises 7

Define the following and give an example of each:

(a) dispersion force

(b) dipole-dipole attraction

Exercises 9

Why do the boiling points of the noble gases increase in the order He < Ne < Ar < Kr < Xe?

Exercises 11

Arrange each of the following sets of compounds in order of increasing boiling point temperature:

(a) HCl, H₂O, SiH₄

(b) F₂, Cl₂, Br₂

(d) O₂, NO, N₂

Exercises 13

On the basis of intermolecular attractions, explain the differences in the boiling points of n–butane (−1 °C) and chloroethane (12 °C), which have similar molar masses.

Exercises 15

The melting point of H₂O(s) is 0 °C. Would you expect the melting point of H₂S(s) to be −85 °C, 0 °C, or 185 °C? Explain your answer.

Exercises 17

Explain why a hydrogen bond between two water molecules is weaker than a hydrogen bond between two hydrogen fluoride molecules.

Exercises 19

Proteins are chains of amino acids that can form in a variety of arrangements, one of which is a helix. What kind of IMF is responsible for holding the protein strand in this shape? On the protein image, show the locations of the IMFs that hold the protein together:

Two turns of a helical structure are shown horizontally. Three Lewis structures are superimposed on the helix. The first shows horizontally stacked dashes next to an oxygen atom, with three dots connecting to a hydrogen atom, and a single dash connecting the hydrogen atom to a nitrogen atom. The second shows a carbon atom double bonded to an oxygen atom, then three dots connecting to a hydrogen atom which is bonded to a nitrogen atom. The third shows a carbon atom double bonded to an oxygen atom with three dots extending to the right of the oxygen atom.

Exercises 21

Identify the intermolecular forces present in the following solids:

(a) CH₃CH₂OH

(b) CH₃CH₂CH₃

Key terms · 8

dipole-dipole attraction: intermolecular attraction between two permanent dipoles
dispersion force: (also, London dispersion force) attraction between two rapidly fluctuating, temporary dipoles; significant only when particles are very close together
hydrogen bonding: occurs when exceptionally strong dipoles attract; bonding that exists when hydrogen is bonded to one of the three most electronegative elements: F, O, or N
induced dipole: temporary dipole formed when the electrons of an atom or molecule are distorted by the instantaneous dipole of a neighboring atom or molecule
instantaneous dipole: temporary dipole that occurs for a brief moment in time when the electrons of an atom or molecule are distributed asymmetrically
intermolecular force: noncovalent attractive force between atoms, molecules, and/or ions
polarizability: measure of the ability of a charge to distort a molecule’s charge distribution (electron cloud)
van der Waals force: attractive or repulsive force between molecules, including dipole-dipole, dipole-induced dipole, and London dispersion forces; does not include forces due to covalent or ionic bonding, or the attraction between ions and molecules

Learn 10.1 on the whiteboard

The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.

Read 10.1 in the textbook · This section on openstax.org