Models of the Atom
Physics: AQA GCSE Higher, topic 3.1.4
The Model of the Atom
Our understanding of atoms has improved over time. The models that we have used to understand atoms have also changed.
Thomson's plum pudding model
- In 1897, an English physicist called J. J. Thomson discovered electrons.
- He modelled the atom as a 'plum pudding' - a ball of positive charge (dough), with negatively charged electrons (currants) mixed in with the 'dough'.
Rutherford's nuclear model
- In 1909, Ernest Rutherford discovered that alpha particles could bounce back off atoms.
- He concluded that an atom's mass is concentrated in the atom's centre. This was called the "nucleus" and it contained positively charged particles called protons.
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The modern model
- Niels Bohr discovered that electrons orbit (fly around) the nucleus at fixed distances.
- In 1932, James Chadwick discovered that some particles in the nucleus have no charge at all. He called them neutrons.
Test yourself on Models of the Atom
Why is Thomson's model of the atom called the 'plum pudding' model?