| 1- Plum Pudding Model | 1) JJ Thomson, 1897 discovered the electron
2) Atoms consisted of a positively charged ball with negative electrons embedded inside
3) Evidence to prove this:
- Solids cant be squashed ∴ the atoms which make them up must be solid throughout
- Rubbing 2 solids together can cause static charge ∴ there must be something (electrons) on the outside of atoms transferred as atoms collide
NOTE: Before this Greek philosopher Demokritos (460-370 BCE) thpought matter was made up of tiny uncuttable pieces - atoms |
| 2- Gold Foil Experiment | 1) Ernest Rutherford, 1905. Directed a beam of (+charge)alpha particles at v. thin gold foil
2) Did this in a suspended vacuum ∴ any deflection of alpha particles would be due to collisions with the gold foil.
3) Most particles went straight through ∴ most of an atom is empty space
4) A few deflected by large angles (>4°) ∴ concentration of +charge in the atom (like charges repel)
5) Very few came straight back ∴ + charge and mass concentrated in a small volume (nucleus) |
| 4- Further Developments | Niels Bohr, 1913.
1) Electrons orbit nucleus at fixed distances/different energy levels from nucleus
2) Chemicals burn with certain-coloured flames ∴ the pattern of energy released by electrons in the chemical reaction, must be the same for every single atom of that element
James Chanwick, 1912/1932
1) There was a difference between the atomic no. and atomic mass of an atom
2) ∴ there had to be a neutral particle the same size as the proton to keep the nucleus stable and make up the missing mass, scientist accepted this 20 years later - 1932 |
