The idea of the atom as the building block of matter has developed over time. What was thought of as a single particle about 1 × 10‾¹⁰ m across is now known to be a collection of smaller particles.

Maths questions often start with the command words ‘Calculate...’ or ‘Determine...’. They will then have a blank space for you to show your working. It is important that you show your working, don’t ...