GCSE Chemistry A (Combined) OCR

States of Matter

States of Matter

Structure and Composition

• All matter is made up of tiny particles. These particles can be atoms, molecules, or ions.
• These particles are constantly moving and/or vibrating.
• The state of matter (solid, liquid, or gas) is determined by the arrangement and energy of these particles.

Solids

• In a solid, the particles are closely packed together in a regular pattern.
• The particles vibrate in fixed positions and do not move around.
• Solids have a fixed shape and volume.
• Solids cannot be compressed because there is no space to reduce between the particles.

Liquids

• In a liquid, the particles are packed less closely than in solids and can move around each other.
• The particles of a liquid are in constant motion, which causes it to take the shape of the container it is in.
• Liquids have a fixed volume but not a fixed shape.
• The ability of liquids to be poured and to take the shape of their containers is referred to as fluidity.
• Liquids also cannot be compressed to any significant extent.

Gases

• In a gas, the particles are much further apart than in liquids and solids.
• The particles in gases have the most energy and they move around freely.
• Gases don’t have a fixed shape or volume and can be easily compressed.
• The particles of a gas have high velocity and constantly collide with each other as well as the sides of the container. This causes pressure.

Changes in State

• Solids can change into liquids through melting. Energy is absorbed during this change.
• Liquids can change into gases through evaporation or boiling. Again, energy is absorbed.
• Gases can change into liquids through condensation, and liquids can change into solids through freezing. These changes release energy.
• Sublimation is a process where a substance changes from solid to gas without even becoming a liquid.
• These changes are all examples of physical changes – they don't change what the substance is.

Particle Model

• The particle model can be used to explain the different states of matter.
• It contains the concepts of particles, energy of particles, and forces between particles.
• A key limitation of the particle model is that it assumes particles are solid spheres, which is not always the case.

For your revision, be sure you understand the particle arrangement in each state, be able to explain why different states have different properties, and recount the changes in state. You should also be well-versed in the particle model, its key concepts, and its limitations.