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Portrait of J. J. Thomson

Science · Physics

J. J. Thomson

1856–1940 · English

Atomic and particle physics

Sir Joseph John Thomson, born near Manchester, discovered the electron in 1897 by showing that cathode rays consist of tiny negatively charged particles far lighter than atoms. As Cavendish Professor at Cambridge he proposed the "plum pudding" model of the atom and, studying positive rays, found the first evidence for isotopes in a stable element. He won the 1906 Nobel Prize in Physics.

How to spot them

  • ▸Discovery of the electron (1897), which he called 'corpuscles'
  • ▸The 'plum pudding' model of the atom
  • ▸Measured the charge-to-mass ratio of cathode-ray particles
  • ▸Cavendish Professor at 28; later Master of Trinity College, Cambridge
  • ▸His son G. P. Thomson won a Nobel Prize for showing electrons behave as waves

Key discoveries & works

Discovery of the electron (1897)

Showed cathode rays are streams of negative particles about a thousandth the mass of a hydrogen atom or less

Measurement of the charge-to-mass ratio of cathode rays (1897)

Deflected the rays with electric and magnetic fields to find e/m

Plum pudding model of the atom (1904)

Electrons embedded in a diffuse sphere of positive charge; overturned by Rutherford

Separation of neon-20 and neon-22 with positive rays (1913)

With Francis Aston, the first evidence of isotopes in a stable element; a forerunner of mass spectrometry

Conduction of Electricity through Gases (1903)

Book summarising the research for which he won the Nobel Prize

Key ideas

  • Atoms are divisible: the electron is a universal constituent of matter
  • Positive-ray analysis sorts ions by mass-to-charge ratio, the principle of the mass spectrometer

Quick-fire facts

  • •Born in Cheetham Hill, Manchester, on 18 December 1856; died in Cambridge on 30 August 1940
  • •Studied at Owens College, Manchester, and Trinity College, Cambridge
  • •Succeeded Lord Rayleigh as Cavendish Professor of Experimental Physics in 1884, aged 28
  • •Nobel Prize in Physics 1906 for investigations into the conduction of electricity by gases
  • •Knighted in 1908; Order of Merit 1912; President of the Royal Society 1915–1920
  • •Master of Trinity College, Cambridge, from 1918 until his death
  • •Many of his students and assistants went on to win Nobel Prizes, including Ernest Rutherford
  • •His son Sir George Paget Thomson shared the 1937 Nobel Prize in Physics for electron diffraction
  • •Buried in Westminster Abbey

Drill it — 7 cards

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Sources