LESSON 8: Atomic Theory
Aristotle[Four Element Theory]
> The four elements theory lasted for about 2000 years.
> It is not a scientific theory because it couldn't be tested against observation.
Democritus
> In 300 B.C., Democritus said atoms were indivisible particles
> First mention of atoms (atomos)
> Not a testable theory, only a conceptual model
> No mention of any atomic nucleus or its constituents
> Cannot be used to explain chemical reactions
Lavoisier (late 1700s)
> Law of conservation of mass
> Law of definite proportions
- water is always 11% H and 89% O
Proust (1799)
> If a compounds is broken down into its constituents, the products exist in the same ratio as in the compound.
> Experimentally proved Lavoisier Laws
Dalton (early 1800s) > Atoms are solid, indestructible spheres (like Billiard balls)
> Provides for different elements (these would be different spheres)
> Based on the law of conservation of mass
> Having a molecule (atoms combine in simple whole # ratios) explains the law of constant composition
> If the atoms are not destroyed, mass does not change
←[TWINS]→
J.J. Thomson (1850s)
> Raisin Bun model
> Solid, positive spheres, with negative particles embedded in them
> First atomic theory to have + (protons) and - (electrons) charges
> Demonstrated the existence of electrons using a cathode ray tube
Rutherford...........'s assistant (1905)
> Showed that atoms have a positive, dense center with electrons outside it
> Resulted in a planetary model
> Explained why electrons spin around nucleus
> Suggests atoms are mostly empty space
~ Loureal & Kim
posted by chemistry11 @ 2:26 PM
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