P2 - Atomic Structure and Theories

what you need to know about atomic structure and the different theories that got it to what it is today

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  • Created on: 29-12-12 11:51
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Atomics Structure and Theories
In 1897, J.J.Thompson discovered negatively charged electrons. A few years later, he knew that
atoms had a neutral overall charge so he said atoms were like a plum pudding. The main part of the
pudding was positive, but there were negatively charged electrons dotted through it. It was
nicknamed the "plum pudding model" because it looked similar to a plum pudding.
A scientist called Ernest Rutherford wanted to see whether the plum pudding theory was correct. So
he and two students (Geiger and Marsden) carried out an experiment. The experiment involved
firing a narrow beam of alpha particles at a very thin sheet of gold foil in a vacuum. They could see
where the alpha particles were hitting and moving to using a detector.
They discovered:
Most alpha particles passed straight through the foil
A few particles were deflected
Very few bounced straight back towards the source
These results didn't fit what the expected if the "plum pudding" model was correct. So after
reaching conclusions based on their evidence, they came up with their own model of the atom.

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Evidence and Conclusions
1. Most alpha particles passed straight through the foil: The atoms in the gold foil contained a
lot of empty space
2. Alpha particles are positively charged, when they are deflected back, they must have been
deflected by a force of repulsion: The atom must contain a small positively charged centre
which we know as the nucleus
3. Alpha particles are heavy, yet some bounced straight back: The nucleus of the atom must be
very small but very dense
4.…read more


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