1.6 Developing the model of the atom
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Describe the plum pudding model of the atom.
Mark scheme
- a ball / sphere of positive charge (1)
- with (negative) electrons embedded in it (1)
Model answer
The atom is a ball of positive charge with negative electrons embedded in it.
In the alpha particle scattering experiment, most alpha particles passed straight through the gold foil, but a few bounced back.
Explain what each observation tells us about the atom.
Mark scheme
- most passed through: atom is mostly empty space (1)
- a few bounced back / deflected: mass concentrated in a small nucleus (1)
- deflection shows nucleus is positively charged (repels positive alpha particles) (1)
- nucleus is very small compared with the atom (1)
Model answer
Most particles passing straight through shows that the atom is mostly empty space. Some being deflected shows the centre is positively charged, repelling the positive alpha particles. A very few bouncing back shows the mass and charge are concentrated in a tiny nucleus.
What did Niels Bohr add to the model of the atom?
Mark scheme
electrons orbit the nucleus at specific distances / in shells / energy levels
Model answer
Electrons orbit the nucleus at specific distances, in shells.
Which particle did James Chadwick provide evidence for?
Mark scheme
neutron
Model answer
The neutron.
Explain why the plum pudding model was replaced by the nuclear model.
Mark scheme
- new evidence from the alpha scattering experiment (1)
- could not be explained by the plum pudding model (1)
Model answer
The results of the alpha scattering experiment could not be explained by the plum pudding model, so a new model was needed.
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