Atomic Theory
Early Atomic theory
In 300 BC, Democritus said atoms were invisible particles/
First mention of atoms/
Not a testable theory, only a conceptual model/
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/
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Lavoisier (late 1700s)
Law of conservation of mass/
Law of definited proportions/
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 ratio as in the compound/
Experimentally provided Lavoisier laws/____________________________________________________
Dalton (Early 1800s)
Atoms are solid, indestructable spheres/
Doesn't mention subatomic particles/
Can't explain isotopes/
No nucleus/
J.J. Thomson (1850)
Raisin bub model/
Solid, positive spheres, with negative particles embedded in them/
First atomic theory to have positive and negative charges/
Introduces nucleus/
No mention of neutrons/
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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 eleectrons spin around nucleus/
Suggests atoms are mostly empty space/Should be unstable/
No nucleus/
Doesn't explain valance level electrons/
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Bohr (1920s)
Electrons must only exist in specific orbitals around nucleus/
Explains how valance electrons are involved in bonding/Explains difference between ionic and covalent bonding/
Resolves the problem of atomic instability/
Includes the neutron/
Explains atomic emisson spectra/
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