The theory of the atomic structure:
- 1) At the beginning of the 19th century, John Dalton described atoms as solid spheres, and different spheres made up different elements.
- 2) In 1897, J J Thompson found out that atoms weren't solid spheres and showed that an atom must contain even smaller, negatively charged particles- electrons.
- This became known as the 'plum pudding model' which showed the atom as a ball of positive charge with electrons stuck in it.
The alpha particle scattering experiment:
- In 1909, Ernest Rutherford conducted an experiment by which he fired positively charged alpha particles at an extremely thin sheet of gold.
- Most of the particles passed straight through the gold sheet, however some particles were deflected more than expected and a small number deflected backwards.
- Rutherford came up with the 'nuclear model' of the atom. In this, there's a tiny positively charged nucleus at the centre, surrounded by a 'cloud' of negative electrons -------------->
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