Electron shells, group and period
Electron shells, group and period

Atoms have a tiny nucleus containing protons and neutrons, with electrons arranged in shells around it. In a neutral atom, the atomic number tells you both the number of protons and the number of electrons.
Step-by-step lessons on OCR GCSE Chemistry Bonding. 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.