The Particle Model (OCR GCSE Chemistry A (Gateway)): Revision Note

The three states of matter are solids, liquids and gases

A substance can usually exist in all three states, dependent on temperature (and pressure)

State changes occur at the melting point (solid to liquid, liquid to solid) and at the boiling point (liquid to gas and gas to liquid)

• Melting and freezing occur at the melting point

• Boiling and condensing take place at the boiling point

• Evaporation is also a change of state and occurs at any temperature; the maximum rate of evaporation occurs at the boiling point 

Individual atoms themselves do not share the same properties as bulk matter

The three states of matter can be represented by a simple model

• In this model, the particles are represented by small solid spheres

A physical change in a substance is a change that does not involve a change in the identity of the substance

A chemical change or chemical reaction is a change in which one or more substances are converted into different substances

The substances that react in a chemical change are called the reactants

The substances that are formed by the chemical change are called the products

A physical change involves changes in the forces between the particles of the substances, but the particles themselves remain the same, as do the chemical properties of the substance

Physical changes are relatively easy to reverse as no new substance is formed during interconversions of state

The interconversions have specific terms to describe them: