There are many people, concepts and features that are important to know when learning Atomic theories, so here are a few important ones to learn:
Four Element Theory (Arostotal)
- Matter is made up of water, wind, earth and fire
- This theory of Arototal's lasted for 2000 years!
- But, isn't a scientific theory because is couldn't be tested against observation
Democritus (4000 BC)
- First mentioned Atoms, and said they were indivisible partices
- This theory was not a testable one though, it was a conceptional one
- There were not any mention of atomic neucleus or it constituients and can't be used to explain chemical reactions
Lavoiser (Late 1700's)
- Introduced the law of conservation of mass and the law of definite proportions
- Water is always 11 % Hydrogen and 89 % Oxygen
Proust (1799)
- Claimed that if a compound is broken down into it's constituients, the products exist in the same ratio as in the compound
Dalton (Early 1800's)
- Aoms are solid, indestructable spheres, just like billiard balls!
- Provides for differet elements
- Explains chemical reactions
- Does not explain isotopes, electricity, attraction, compulsion, etc..
JJ Thompson (1850's)
- Proposed the raisin bun model
- Solid, positive spheres with negative particles embedded in them
- First atomic theory to have positive (protons) and negative (electrons) charges
- Demonstrated existance of electrons using cathode ray tubes
Rutherford (1905)
- Showed that atoms have a positive, dense, centre with electrons outside it which resulted in a planetary model
- Suggested that atoms are mostly empty space
