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Physics Paper 1 · P4 · Lesson 4.1

Inside an atom

Start with the centre of an atom and three tiny particles.

Key ideas1 of 3

Meet the nucleus

The nucleus is the tiny centre of an atom. It contains protons and neutrons. Electrons are outside the nucleus.

A helium atom schematic: a central nucleus contains two red positive protons and two green neutrons; two blue negative electrons are outside.

A simple helium atom model. The nucleus is enlarged so you can see it.

Next: Atomic number, mass number and isotopes →
Topic resources and sources

Daily 5 · Core exam practice · Higher Tier questions · A4 revision sheet

Lessons 4.1–4.10 cover the core. Lesson 4.11 is Higher Tier only. Daily 5 practises core facts. Answer positions are shuffled on each new attempt; lessons begin with very simple questions.

AQA Combined Science Trilogy specification · 6.4.1.1–6.4.1.2. Original notes, questions and diagrams. Experimental numbers are illustrative.

Photos: Geiger counter by Boffy b, enhanced by Marco Plassio; caesium source by Wusel007, enhanced by Partynia, both CC BY-SA 3.0. Rutherford at McGill, 1905, unknown photographer / Wellcome Images, public domain. Photos displayed without cropping or other alterations.