History of the atom
- Created by: Khadija
- Created on: 15-02-20 13:12
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- The history of an atom
- John Dalton
- In the 19th century he described atoms as solid spheres.
- Different spheres made up of different elements.
- J J Thomas
- In 1897 he concluded from his experiment that atoms weren't solid spheres.
- His measurement for charged and mass showed even smaller negatively charged particles - electrons.
- The Plum pudding model
- Showed atom as a ball of positive charge with electrons stuck in it.
- Ernest Rutherford
- In 1909 he and his student carried out alpha particle scattering experiments.
- They fired positively charged alpha particles at a thin sheet of gold.
- From plum pudding model expected particles to pass straight sheet or deflect back.
- As the +charge of atom was thought to be spread out through 'pudding' of atom.
- Most particles went straight through, some deflected back more than expected so plum pudding couldn't be right.
- Nuclear model of atom to explain evidence.
- Tiny, positively charged nucleus at centre, where mass is concentrated.
- Cloud of negative electrons surrounds nucleus so most atom is empty space.
- When alpha particles go near nucleus they were deflected. If fired directly at nucleus they deflected backwards, if not they pass through empty space.
- In 1909 he and his student carried out alpha particle scattering experiments.
- Niels Bohr
- In 1914 his Nuclear model of atom suggested all electrons were contained in shells.
- Electrons orbit the nucleus in fixed shells which have fixed distance from the nucleus.
- Excited electrons fall from a high to a low energy level.
- James Chadwick
- Two types of subatomic particles in the nucleus
- Had evidence of protons but not of the second sub-atomic particle. Hard to detect as it has no charge but same mass of protons.
- In 1932 he did an experiment that explained the existence of neutrons
- John Dalton
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