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Thomson was born in a town near Manchester. He always wanted to be an engineer but when he was awarded a scholarship in honour of John Dalton, he accepted and studied chemistry. At the age of 28, he was named professor at the Cavendisch Laboratory, Cambridge University.
What did Thomson do?
Electricity has long been though of as a stream positive particles but after collecting data for 20 years, Thomson was convinced they were actually negative particles he called electrons. He was even able to measure the mass of the electron. This measurement didn’t convince the scientific establischement.
Thomson asked Wilson to try an photograph the electron and in 1911, he succeeded. Thomson was a bit hesitant to tell the world about his discovery because until then, the atom had always been considered a solid particle.
Thomson’s model of atomic structure – 1899
Atoms consisted of rings of negative electrons embedded in a sphere of positive “soup” (the plum pudding model).
The positive and negative charges balance to make the atom neutral.
The mass of the atom was due to the “nucleus”.
The mass of an electron was 1/1840 of the mass of a hydrogen nucleus, the lightest atom.
There was only one electron in an atom of hydrogen.
Assignments
12. Explain why Thomson’s model is called the plum pudding model (krentebolmodel).
13. Draw an atom of Lithium according to Thomson.
14. What is the biggest difference between this new model and that of Dalton?
15. Name a similarity between this model and that of Dalton.
16. Which technological advance helped Thomson’s idea to be accepted?
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