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Physics Paper 1 · P4 · Lesson 4.4

How the atomic model changed

Use evidence to see why scientists changed their ideas.

Key ideas1 of 5

From a sphere to plum pudding

Early models treated atoms as tiny, indivisible spheres. After the electron was discovered, the plum pudding model placed negative electrons inside a spread-out positive charge.

Three models: a solid indivisible sphere; a sphere of spread-out positive charge with embedded negative electrons; and a small positive nucleus with electrons outside.

The single large + represents the spread-out positive charge.

Next: What is radioactivity? →
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 · 6.4.1.3. 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.