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KS3 Science - Atomic History Timeline: Thomson

How ideas about the atom developed - evolution of the atomic model

Sir JJ Thomson


Born in Manchester in 1856, Joseph John Thomson (known as 'J.J.') studied at Owen's College (now Manchester University) and moved to Cambridge to study mathematics. In 1884, aged 27, he became Cavendish Professor of Physics and Head of the Cavendish Laboratory. The Laboratory had opened in 1874 under James Clerk Maxwell, who was well known for his work on electricity and magnetism.


Thomson's atomic Model

Main Points

** Raisin bun model

** Infers the existence of electrons and protons

** Introduces nucleus

Thomson held that atoms are uniform spheres of positively charged matter in which electrons are embedded. Popularly known as the plum-pudding model, it had to be abandoned (1911) on both theoretical and experimental grounds in favour of the Rutherford atomic model, in which the electrons describe orbits about a tiny positive nucleus

Thomson's most important work

Thomson’s most important line of work, was that which led him in 1897 to the conclusion that all matter, whatever its source, contains particles of the same kind that are much less massive than the atoms of which they form a part. They are now called electrons, although he originally called them corpuscles. His discovery was the result of an attempt to solve a long-standing controversy regarding the nature of cathode rays which occur when an electric current is driven through a vessel from which most of the air or other gas has been pumped out.


Shortfall of Thomson's model

  • Existence of electrons not considered
  • Existence and role of neutrons not explained