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Chemistry

Workhorse studio concept for the American Association of Chemistry Teachers. This app has not been commissioned or approved by AACT.

MapUnit 2, Bonding and forces

2.1Intermolecular forces

The attractions between molecules, and why they set boiling point and vapor pressure.

Compare molecular attractions

Warm two substances and inspect what happens at their reference transition temperatures.

Temperature sweep-67 °C

Reference pressure1 atm

Ethanol

Each dot represents one whole molecule
Below its boiling point: boils at 78 °C at 1 atm.
Electrons per molecule
26
Polar molecule
Yes

London dispersion forces · Dipole-dipole interactions · Hydrogen bonding

Propane

Each dot represents one whole molecule
Below its boiling point: boils at −42 °C at 1 atm.
Electrons per molecule
26
Polar molecule
No

London dispersion forces

Ethanol: 78 °CPropane: -42 °C-67 °C103 °C
Move the temperature control or heat both to compare the transitions.

Drag to inspect a stage. Playback shows the sequence, not elapsed physical time.

Experiment results

Complete a run to keep its result here. Change the setup to compare another run.

About this model

This comparison uses stored reference boiling points and molecule properties. The controllable temperature sweep reveals those values. Particle spacing illustrates separation at the transition; it does not calculate boiling points, melting points, heat transfer or molecular trajectories. Below a transition, the diagram does not distinguish solids from liquids. Carbon dioxide is marked as subliming.

Reference: OpenStax, Phase Transitions

Guided investigations and notebook

Investigation 1 of 2

What makes one substance boil before another?

Ethane and ethanol are about the same size. Heat both and see which boils first.

  1. Predict

    Which boils at the higher temperature?

    Make a guess before you run it. Being wrong here is useful.

  2. Run it

    Compare molecular attractions

    Warm two substances and inspect what happens at their reference transition temperatures.

    Temperature sweep-114 °C

    Reference pressure1 atm

    Ethane

    Each dot represents one whole molecule
    Below its boiling point: boils at −89 °C at 1 atm.
    Electrons per molecule
    18
    Polar molecule
    No

    London dispersion forces

    Ethanol

    Each dot represents one whole molecule
    Below its boiling point: boils at 78 °C at 1 atm.
    Electrons per molecule
    26
    Polar molecule
    Yes

    London dispersion forces · Dipole-dipole interactions · Hydrogen bonding

    Ethane: -89 °CEthanol: 78 °C-114 °C103 °C
    Move the temperature control or heat both to compare the transitions.

    Drag to inspect a stage. Playback shows the sequence, not elapsed physical time.

    Experiment results

    Complete a run to keep its result here. Change the setup to compare another run.

    About this model

    This comparison uses stored reference boiling points and molecule properties. The controllable temperature sweep reveals those values. Particle spacing illustrates separation at the transition; it does not calculate boiling points, melting points, heat transfer or molecular trajectories. Below a transition, the diagram does not distinguish solids from liquids. Carbon dioxide is marked as subliming.

    Reference: OpenStax, Phase Transitions

    What the bench showed

    Nothing yet. Each run adds a line here.

  3. Say what you found

  4. Check

    2 questions about what the bench shows open once your finding is in the notebook.

Investigation 2 of 2

Same forces, different size

Pentane and hexane are both non-polar, so both have London dispersion forces only. Does size still matter?

  1. Predict

    Which boils at the higher temperature?

    Make a guess before you run it. Being wrong here is useful.

  2. Run it

    Compare molecular attractions

    Warm two substances and inspect what happens at their reference transition temperatures.

    Temperature sweep11 °C

    Reference pressure1 atm

    Pentane

    Each dot represents one whole molecule
    Below its boiling point: boils at 36 °C at 1 atm.
    Electrons per molecule
    42
    Polar molecule
    No

    London dispersion forces

    Hexane

    Each dot represents one whole molecule
    Below its boiling point: boils at 69 °C at 1 atm.
    Electrons per molecule
    50
    Polar molecule
    No

    London dispersion forces

    Pentane: 36 °CHexane: 69 °C11 °C94 °C
    Move the temperature control or heat both to compare the transitions.

    Drag to inspect a stage. Playback shows the sequence, not elapsed physical time.

    Experiment results

    Complete a run to keep its result here. Change the setup to compare another run.

    About this model

    This comparison uses stored reference boiling points and molecule properties. The controllable temperature sweep reveals those values. Particle spacing illustrates separation at the transition; it does not calculate boiling points, melting points, heat transfer or molecular trajectories. Below a transition, the diagram does not distinguish solids from liquids. Carbon dioxide is marked as subliming.

    Reference: OpenStax, Phase Transitions

    What the bench showed

    Nothing yet. Each run adds a line here.

  3. Say what you found

  4. Check

    2 questions about what the bench shows open once your finding is in the notebook.

What this topic builds

  • Name the forces between a substance’s moleculesNot practiced yet.
    Not started
  • Compare two substances by boiling point or vapor pressureNot practiced yet.
    Not started
  • Put three substances in order of their forcesNot practiced yet.
    Not started
Next: Learn

Built from AACT’s 2020 simulation, Intermolecular Forces Quiz.