GCSE · Chemistry · AQA · Spec 8462

Properties of small molecules

Why are melting and boiling points low?

?

Reason it through

Why do substances made from small molecules usually have relatively low melting and boiling points?

Link 1 of 4

First link · your turn

First, where are the weak forces in a molecular substance?

2
Locked — reveal the link above first
3
Locked — reveal the link above first
4
Locked — reveal the link above first

Inside a molecule vs between molecules

Covalent bondsvsIntermolecular forces

This is the distinction that unlocks the whole topic.

Focus

Where are they?

Covalent bonds

Within each molecule

Intermolecular forces

Between separate molecules

The insight

The two forces act in different places, so do not treat them as the same thing.

Relative strength

Covalent bonds

Strong

Intermolecular forces

Weak by comparison

During melting

Covalent bonds

Not overcome

Intermolecular forces

Overcome

During boiling

Covalent bonds

Not overcome

Intermolecular forces

Overcome

What happens when it melts or boils?

Track which forces are overcome as the substance is heated.

Relationship matrix

Tap any cell to reveal it. Tap a column header to read one property down every item.

Intermolecular forcesMelting pointBoiling point
Smaller molecules
Larger molecules

Each cell hides a short answer and the reason behind it. Predict before you tap.

What actually breaks?

Commit to an answer before revealing the explanation.

A small-molecule substance boils. Which statement best describes what has been overcome?

Explain the properties from the structure

Problem

A substance consists of small molecules. Explain why it has a relatively low boiling point and does not conduct electricity.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

Strong bonds inside each molecule, weak forces between molecules — that distinction explains the properties.

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