AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
Students should be able to explain the differences in density between the…
Full specification wording
Density of materials: Students should be able to explain the differences in density between the different states of matter in terms of the arrangement of atoms or molecules.
Density is mass per unit volume, ρ = m ÷ V, so it depends on how closely the particles are packed rather than on how heavy each particle is.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 2 of 3
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Density is mass per unit volume, ρ = m ÷ V, so it depends on how closely the particles are packed rather than on how heavy each particle is. In a solid the particles touch and are regularly arranged, so a large number fits into a small volume and the density is high. A liquid of the same substance is usually only slightly less dense, because its particles still touch but are disordered with a few extra gaps. A gas is far less dense, often about a thousand times less, because the same number of particles is spread through a much larger volume with large empty spaces between them. Helium of mass 0.00254 kg filling 0.0141 m³ has a density of only 0.18 kg/m³, compared with about 1000 kg/m³ for water.
What earns the marks
- Density stated as mass per unit volume, ρ = m ÷ V.
- Solid particles being close together in a regular arrangement, giving a high density.
- Gas particles being far apart, so the same mass occupies a much larger volume.
- A liquid being close in density to the solid because its particles still touch.
Common mistakes and how to put them right
Saying a gas is less dense because its particles are lighter or smaller.
Claiming a gas has less mass than the solid it came from, when mass is conserved on a change of state.
Giving the unit as m³/kg instead of kg/m³.
Stating that a liquid is always exactly halfway in density between the solid and the gas.
Exam tips
- Always answer in terms of the number of particles in a given volume, not the size of the particles.
- Choose the unit carefully in multiple-choice unit questions, since density is mass divided by volume, so kg/m³.
- Quote a real comparison, such as air against water, to show the scale of the difference.
Try the lesson
The start of the Density of materials: Students should be able to explain the differences in density between the different states of matter in terms of the arrangement of atoms or molecules. lesson, made from checked teaching notes for this specification point.
Have a go first
In terms of the arrangement of particles, why is a gas much less dense than a solid?
Listen
Density is mass per unit volume, ρ = m ÷ V, so it depends on how closely the particles are packed rather than on how heavy each particle is. In a solid the particles touch and are regularly arranged, so a large number fits into a small volume and the density is high. A liquid of the same substance is usually only slightly less dense, because its particles still touch but are disordered with a few extra gaps. A gas is far less dense, often about a thousand times less, because the same number of particles is spread through a much larger volume with large empty spaces between them. Helium of mass 0.00254 kg filling 0.0141 m³ has a density of only 0.18 kg/m³, compared with about 1000 kg/m³ for water. A strong answer earns marks for these points. density stated as mass per unit volume, ρ = m ÷ V. solid particles being close together in a regular arrangement, giving a high density. gas particles being far apart, so the same mass occupies a much larger volume. a liquid being close in density to the solid because its particles still touch. Exam tip: Always answer in terms of the number of particles in a given volume, not the size of the particles.
Key words
Say what each word means before you turn the card.
density
Try answering aloud or in your head before turning the card.
particle spacing
Try answering aloud or in your head before turning the card.
states of matter
Try answering aloud or in your head before turning the card.
units of density
Try answering aloud or in your head before turning the card.
See every definition
- density
- Mass per unit volume, ρ = m ÷ V, depending on how closely the particles are packed rather than on how heavy each particle is.
- particle spacing
- How closely particles are packed: in a solid they touch and are regularly arranged, while in a gas large empty spaces lie between them.
- states of matter
- Solid, liquid and gas forms, differing in density because of the arrangement of atoms or molecules and the gaps between them.
- units of density
- Kilograms per cubic metre, kg/m³, since density is mass divided by volume.
There is more to this lesson
The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Test your understanding of Density of materials: Students should be able to explain the differences in density between the different states of matter in terms of the arrangement of atoms or molecules.
Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge