Atomic Theory [Joanne]

Early Atomic Theory

-GREEK

- In 300 B.C., Democritus said atoms were invisible particles,

- First mention of atoms (atomes)

- Not a testable theory, only a conceptual model

- No mention of any atomic nucleus or its constituents

- Cannot be used to explain chemical reactions

- This theory was the most accepted view for over 2000 years


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Lavoisier (late 1700s)

- Law of Conservation of Mass

- Law of definite proportions

- Wasn't a true atomic theory because it didn't discuss what atoms were arranged

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Proust (1799)

- If a compound is broken down into its constituents, the products exist in the same ratio as in the compound

- Experimentally proved Lavoisier Laws

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Dalton (early 1800s)

- Atoms are solid, indestructible spheres (like Billard balls)

- Provides for different elements (these would be different spheres)

- Doesn't metntion subatomic particles

- Can't explain isotopes
- Didn't mention the nucleus

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J.J. Thomson (1850s)
- Raison Bun Model
- Solid, positive spheres, with negative particles embedded in them
- First atomic theory to have positive (protons) and negative (electrons) charges
- Introduces idea of nucleus
- Didn't mention neutrons, so radioactive decay could'nt be explained
- Doesn't explain how electrons can exist outside nucleus
- Doesn't explain electrons role in chemical bonding








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Rutherford (1905)
- Showed that atoms have a positive, dense center with electrons outside it
- Resulted in a planetary model
- Explains why electrons spin around the nucleus
- Suggests atoms are mostly empty space
- Didn't mention neutrons
- Doesn't explain valence level electrons role in chemical bonds

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Bohr (1920s)

- Electrons MUST only exist in specific orbitals around nucleus

- Explains how valence elctrons are involved in bonding

- Explains the difference between ionic and covalent bonding

- Resolve the neutron (discovered in 1932)

- Explains atomic emission spectra

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