Particle Model and Gases

Section: Chemistry | Syllabus: Cambridge Primary Stage 5 Science (0097)

Solids, Liquids, Solutions and Gases

The particle model describes all matter as being made of tiny particles, and it is used to explain the different states of matter.
Heating or cooling a substance changes how its particles move and how far apart they are spaced - it does not change the size or mass of the particles themselves.

Particles are arranged and move differently in solids, liquids and gases

State	Particle arrangement and movement	Properties
Solid	Touching in a regular arrangement; vibrate in place	Fixed shape and volume
Liquid	Touching, irregular and able to move past one another	Flows; fixed volume
Gas	Far apart, random and moving quickly	Flows; fills a container; easily compressed
Solution	Solute particles spread among solvent particles	Looks evenly mixed

Particles do not disappear when a substance dissolves - they are simply spread among the particles of the solvent.

Common gases at room temperature include oxygen, carbon dioxide, water vapour, nitrogen and hydrogen.
A gaseous substance can be present even when it cannot be seen - most gases are invisible.
Water vapour is invisible water in the gas state; visible mist or steam clouds are actually made of tiny liquid water droplets, not gas.

Worked Example: Drawing a Gas Model

Question: Describe how to complete a particle diagram for hydrogen gas in a box. [2]

Hydrogen is a gas at room temperature. Gas particles should be far apart and randomly placed, not touching. Answer

Draw a small number of identical particles far apart and randomly arranged throughout the box.

MistakeGas particles rise and stay only at the top of a container.

FixGas particles move in all directions and spread evenly through the available space.

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