The Atom

The Atom

1. Greeks - matter is composed of atoms

2. John Dalton - Dalton's Atomic Theory: all matter is made up of small particles called atoms, Atoms are indivisible and cannot be created or destroyed.

3. Crookes - Maltese cross inside a cathode ray tube. A shadow was cast by the cathode rays, therefore radiation was coming from the negative plate; the cathode. Paddle wheel in front of cathode The paddle wheel moved therefore particles were coming from the cathode.

4. Thompson - Set up an experiment to see if these particles were charged. He deflected cathode rays upwards towards a positive plate, therefore cathode rays are negatively charged particles. He calculated the ratio of the charge of the electron to its mass. e/m = charge/mass.

5. Thompson discovered the electron

6. Millikan - Millikan's oil drop experiment. He calculated the charge of the electron, therefore the mass of the elextron

7. Thompson - Since atoms are neutral, there must be positive charges also in the atom to neutralise the negative electrons. Thompson's plum pudding model is a sphere of positive charge with negative charge embedded in it at random

8. Rutherford - Discovered the nucleus. Gold foil was bombarded with alpha particles. A zinc sulphide detector was used to detect the scattered alpha particles. Slight deflections were expected. Most of the alpha particles went straight through the foil as expected. There were some very large deflections and some particles were delfected back along their own path. Conclusion: there is a small, dense positively charged core called the nucleus.

9. Rutherford discovered the proton

10. Chadwick - Bombarded lithium and beryllium with alpha particles and neutral particles were given off