Development of the atom and periodic table
- Created by: Abc312
- Created on: 08-05-18 18:26
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- Developments in science
- Development of the Periodic Table
- Before protons, neutrons and electrons scientist classified elements by arranging them in order of atomic weights.
- In early periodic tables some elements were placed in the wrong group if atomic weight order was strictly followed.
- Dmitri Mendeleev overcame some problems by leaving gaps for elements that he thought hadn't been discovered.
- He mainly followed atomic mass but switched the place if the properties meant it should be changed
- Elements with properties that had been predicted by Mendeleev were eventually discovered
- When the elements were discovered and they fitted the pattern this backed up Mendeleev's ideas.
- As isotopes were discovered this explained why elements couldn't always be ordered by atomic weight.
- Dmitri Mendeleev overcame some problems by leaving gaps for elements that he thought hadn't been discovered.
- In early periodic tables some elements were placed in the wrong group if atomic weight order was strictly followed.
- Before protons, neutrons and electrons scientist classified elements by arranging them in order of atomic weights.
- Development of the atom
- Before the discovery of the electron, atoms were thought to be tiny spheres that couldn't be divided
- The discovery of the electron led to the plum pudding model.
- This suggested the atom was a ball of positive charge with negative electrons spread throughout.
- Ernest Rutherford proved this was wrong when he carried out the alpha scattering experiment.
- This involved firing positively charged alpha particles at a thin sheet of gold.
- They were expecting the particles to pass straight through or only be slightly deflected.
- Most particles did pass straight through but some were deflected more than expected and some deflected backwards
- The experiment proved that the mass of the atom was concentrated at the centre so the nucleus was 'created'.
- The nuclear model replaced the plum pudding model
- Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances.
- The electrons had to be in shells because if they were in clouds like first suggested the atom would collapse.
- This theory was backed up by lots of experimental observations.
- Further experiments led to the idea that the positive charge of the nucleus could be subdivided into smaller particles.
- Each of these particles had the same amount of charge and they were called protons.
- James Chadwick proved evidence that there were neutral particles in the nucleus.
- They were called neutrons.
- Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances.
- The discovery of the electron led to the plum pudding model.
- Before the discovery of the electron, atoms were thought to be tiny spheres that couldn't be divided
- Development of the Periodic Table
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