Intermolecular Forces Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Intermolecular Forces.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

Intermolecular forces are attractions between separate particles, usually molecules, rather than bonds within a single molecule.

These are the attractions between neighboring particles, not the bonds holding each particle together.

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How to Use These Examples

Read the first worked example with the solution open so the structure is clear.
Try the practice problems before revealing each solution.
Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Intermolecular Forces starts by identifying valence electrons, likely charges or sharing, and the structure that follows.

Common stuck point: Students often know a formula related to intermolecular forces but skip the recognition step: Am I explaining a substance by electron behavior, bond type, molecular shape, polarity, or attractions between particles? That leads to a correct-looking substitution attached to the wrong chemical model.

Sense of Study hint: Ask: Am I explaining a substance by electron behavior, bond type, molecular shape, polarity, or attractions between particles?

Worked Examples

Example 1

medium

Why does

CCl_4

boil at 77 °C while

CH_4

boils at -164 °C, both being nonpolar?

CCl₄: four equal C-Cl dipoles cancel by symmetry → nonpolar, but many electrons → strong dispersion

Answer

CCl_4 \text{ has many more electrons and stronger dispersion}

First step

Both molecules are tetrahedral and nonpolar; only dispersion acts.

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Example 2

medium

Pentane bp 36 °C, hexane bp 69 °C, heptane bp 98 °C. Why does bp rise within this series?

Example 3

hard

For

CH_4

(bp -161 °C) vs

SiH_4

(bp -112 °C), explain the trend using IMFs.

Example 4

challenge

Predict and explain whether

CH_3F

CH_3OH

has the higher boiling point.

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy

Are intermolecular forces attractions WITHIN a molecule or BETWEEN molecules?

Example 2

easy

Which intermolecular force is present in ALL molecules?

Example 3

easy

Rank the three IMF types by increasing typical strength: dispersion, dipole-dipole, hydrogen bonding.

Example 4

easy

Which IMF acts between two nonpolar

O_2

molecules?

Example 5

easy

What special IMF occurs when H is bonded to N, O, or F?

Example 6

easy

Are intermolecular forces generally stronger or weaker than covalent bonds?

Example 7

easy

Which has stronger intermolecular forces: water (hydrogen bonding) or methane (dispersion only)?

Example 8

easy

Do larger nonpolar molecules tend to have stronger or weaker dispersion forces?

Example 9

medium

Why does water boil at a much higher temperature than

H_2S

despite both being bent

AH_2

molecules?

H₂O: bent geometry with lone pairs allows hydrogen bonding, absent in H₂S

Example 10

medium

Which IMFs act in liquid

HCl

(polar, no H bonded to N/O/F)?

Example 11

medium

Rank the boiling points of

CH_4

H_2O

, and

HCl

from lowest to highest.

Example 12

medium

Why does

NH_3

have a higher boiling point than

PH_3

NH₃: N-H bonds plus lone pair enable hydrogen bonding; PH₃ lacks this

Example 13

medium

Between pentane and 2,2-dimethylpropane (same formula

C_5H_{12}

), which has the higher boiling point?

Example 14

medium

Why does ice float on liquid water?

Example 15

medium

Identify the strongest IMF in liquid ethanol

CH_3CH_2OH

Example 16

medium

Why does increasing IMF strength generally raise a liquid's boiling point?

Example 17

medium

Which has the higher boiling point:

F_2

Cl_2

, and why?

Example 18

challenge

Explain why HF (bp 20°C) boils higher than HCl (bp -85°C) even though HCl has more electrons.

Example 19

challenge

Noble gases He, Ne, Ar have rising boiling points down the group. Explain using IMFs.

Example 20

challenge

Glycerol

C_3H_8O_3

is far more viscous than ethanol. Explain using IMFs.

Example 21

easy

Which IMF acts between two argon (

Ar

) atoms?

Example 22

easy

Are intermolecular forces stronger or weaker than the covalent bonds within a molecule?

Example 23

easy

Which IMFs act in liquid

CO_2

(a nonpolar molecule)?

CO₂: linear symmetry cancels both C=O dipoles → nonpolar → London dispersion only

Example 24

easy

Which property is most directly governed by IMF strength: covalent bond length, boiling point, or atomic number?

Example 25

easy

Which has stronger dispersion forces:

I_2

F_2

Example 26

easy

Are dispersion forces present in polar molecules too?

Example 27

easy

Do IMFs hold atoms together inside a single

H_2O

molecule?

Example 28

medium

Rank the boiling points of

Ne

Ar

Kr

Xe

from lowest to highest.

Example 29

medium

Which IMFs act between two

CH_3Cl

molecules?

CH₃Cl: the lone Cl breaks tetrahedral symmetry, leaving a net dipole → dipole-dipole + dispersion

Example 30

medium

Predict which has the higher viscosity: hexane

C_6H_{14}

or glycerol

C_3H_8O_3

Example 31

medium

Rank IMFs in liquid water: H-bond, dispersion, dipole-dipole. Which is the strongest contributor?

Example 32

medium

Why does cooking oil not mix with water?

Example 33

medium

Which has the higher boiling point:

CH_3OCH_3

(dimethyl ether) or

CH_3CH_2OH

(ethanol)? Both are

C_2H_6O

Example 34

medium

Which IMFs act in liquid

NH_3

NH₃: polar pyramidal shape + N-H bonds → hydrogen bonding + dipole-dipole + dispersion all present

Example 35

medium

Which IMF type makes ion-dipole interactions in NaCl(aq) possible (between

Na^+

and water)?

Example 36

medium

Predict whether

CO_2

dissolves better in water or in hexane.

Example 37

medium

Which has stronger IMFs:

Cl_2

Br_2

Example 38

medium

Why is petroleum jelly (long hydrocarbons) a solid/semi-solid while gasoline (shorter hydrocarbons) is a liquid at room temperature?

Example 39

hard

Identify the strongest IMF in liquid acetic acid

CH_3COOH

Example 40

hard

Why does isopropanol

(CH_3)_2CHOH

evaporate from skin and feel cool?

Example 41

hard

A student says branching always lowers boiling point in isomers. Why is this true for alkanes?

Example 42

hard

Predict which is more volatile: acetone

(CH_3)_2CO

or 1-propanol

CH_3CH_2CH_2OH

. Both have similar molar mass.

Example 43

hard

Explain why noble gases can be liquefied at all if they have only dispersion forces.

Example 44

challenge

A student claims that ion-dipole forces are 'just very strong dipole-dipole forces.' Critique this in one sentence and indicate the correct relationship.

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Related Concepts

Molecular Polarity Hydrogen Bonding State of Matter

Background Knowledge

These ideas may be useful before you work through the harder examples.

polarity