the history of the atom
- Created by: tia5sos
- Created on: 17-11-20 18:53
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- the history of the atom and atomic structure
- in 1897 JJ Thompson figured that atoms weren't solid spheres
- his measurements of charge and mass showed that an atom must contain smaller, negatively charged particles - electrons.
- From his results, he made a model of the atom known as the 'plum pudding model'
- his measurements of charge and mass showed that an atom must contain smaller, negatively charged particles - electrons.
- or the thomson model
- this is where negative electrons were spread through a positive 'pudding' that made up most of the atom
- in 1909 Ernest Rutherford, working with Hans Geiger and Ernest Marsden, conducted the famous gold foil experiment.
- they fired positively charged alpha particles at an extremely thin sheet of gold
- from the plum pudding model they expected the particles to pass straight through the gold sheet or only be slightly deflected.
- but although most of the particles did go straight through the sheet, some were deflected more than they had expected..
- ...and a few were deflected back the way they had come - something the plum - pudding model couldn't explain.
- but although most of the particles did go straight through the sheet, some were deflected more than they had expected..
- from the plum pudding model they expected the particles to pass straight through the gold sheet or only be slightly deflected.
- they fired positively charged alpha particles at an extremely thin sheet of gold
- Rutherford came up with the theory of the nuclear atom to explain this new evidence
- in his model, most of the mass of an atom is concentrated in a tiny, positively charged nucleus at the centre...
- ...surrounded by a 'cloud' of negative electrons - most of the atom is empty space.
- in his model, most of the mass of an atom is concentrated in a tiny, positively charged nucleus at the centre...
- scientists realized that electrons in a 'cloud' around the nucleus of an atom like this would be attracted to the nucleus, causing the atom to collapse
- Niels Bohr got round this a few years later by proposing a new model where the electrons are in shells.
- he suggested that electrons can only exsist in these shells (or fixed orbts), and not anywhere in - between.
- his theory was pretty close to the model of the atom shown on the 'the atom is made up of protons, neutrons and electrons' mindmap :)
- he suggested that electrons can only exsist in these shells (or fixed orbts), and not anywhere in - between.
- in 1897 JJ Thompson figured that atoms weren't solid spheres
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