Isotopes: same element, different mass
Isotopes: same element, different mass

Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. The number of protons is the atomic number, so it stays the same for all isotopes of an element.
Step-by-step lessons on AQA GCSE Chemistry 1.1.6 Relative atomic mass. Each one builds up to exam-style questions. Nail the core quantitative topics — moles, balancing equations and calculations — early on, since they underpin higher-tier questions across every paper and topic.