© Thom Leach/Science Photo Library
The terms in bold link to topics in the AQA, Edexcel, OCR, WJEC and CCEA A-level specifications, as well as the IB, Pre-U and SQA exam specifications.
Atoms are composed of protons, neutrons and electrons. Electrons are part of a family of fundamental particles called leptons, whereas protons and neutrons are hadrons, a type of particle made of quarks. At a subatomic level particles exhibit properties that can be categorised using quantum numbers, such as the baryon number, the lepton number or strangeness. Spin is another example of a quantum number, used here to describe properties of electrons.
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