Greeks
- In 300 BC Democritus said atoms were indivisible particles
- This is the first mention of atoms ( atomos )
- It was only a conception model. It wasn't testable
- There was no mention of any atomic nucleus or its constituents
- Can't be used to explain chemical reactions
- This theory was the most accepted view for over 2000 years
Lavosier (late 1700s)
- Law of conservation of mass
- Law of definite proportions
- BUT his theory wasn't a true atomic theory because it didn't discuss what atoms were or how they were arranged
Proust (1799)
- If a compound is broken down into its constituents, the products exist in the same ration of compound
- Experimentally proved lavoisier laws
Dalton (early 1800s)
- Atoms are solid, inde
structible spheres ( like billiard balls)
- Provides for different elements (Different Spheres)
- Doesn't mention subatomic particles
- Can't explain isotopes
- No mention of nucleus
- No Valence shells
JJ Thompson (1850s)
- Raisin bun model
- solid, positive spheres with negativeparticales embedded in them
- He was the first to mention the negative and positive charge of electrons and protons
Introduced the idea of a nucleus - No neutrons mentions so radioactive decay can't be explained
- Doesn't explain how electrons can exist outside of nucleus
- Doesn't explain electrons role in chemical bonding
Rutherford(1905)
- Showed that atoms have a positive, dense center with electrons outside
- Rusulted in a planetary model
- Explains why electrons spin around nucleus
- Suggests atoms are mostly empty space
- Should be unstable( electrons and protons should attract and destroy atom)
- No mention of reactions
- doesn't explain valence level electrons role in chemical bonds
Bohr (1920s)
- Electrons must only exist in specific orbitals around nucleus
- Explains how valence electrons are involved in bonding
- Explains diference between ionic and covalent bonding
- Resolves problem of atomic instability
- Explains atomic emission spectra