Chemistry 11

Four Element Theory

wetness

water wind

coldness hotness

earth fire

dryness

-the four elements theory lasted for about 2000 years

-it's not a scientific theory because it could not be tested

-in 300BC Democritus said atoms were invisible particles

-this was the first mention of atoms in history

-not a testable theory only a conceptual model

-no mention of any atomic nucleus

-cannot be used to explain chemical reactions

Lavoisier (late 1700's)

-law of conservation of mass

-law of definite proportions (water is always 11% H and 89% O)

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's laws

Dalton (early 1800's)

-atoms are solid, indestructible spheres (billard balls)

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

-based on the law of conservation of mass

-having a molecule(atoms combine in whole number ratios) explains the law of constant composition

J.J Thomson (1850's)

-raisin bun model

-solid, positive spheres with negative particles embedded in them

-first atomic theory to have positive (protons) and negative (electrons) charges

-demonstrated the existence of electrons using a cathode ray tube

Rutherford (1905)

-showed that atoms have a positive, dense center, with electrons outside it

-resulted in a planetary model

-explains why electrons spin around nucleus

-suggests atoms are mostly empty space

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-Kerr Pili

Thursday, October 14, 2010