Atomic Theory
Wednesday, October 13, 2010 /8:05 PM
Atomic Theory
Aristole [European view]:
Four element theory (water, earth, wind, and fire)
- the four element theory lasted around 2000 years
- it is not a scientific theory because it could not be tested against observation
Democritus [European view]:
- in 300 B.C Democritus said atoms were indivisble particles
- first mention of atoms [atomos]
- it is not a testable theory, only a conceptual model
- he didn't know any atomic nucleus or its constituents
- cannot be used to explain chemal reactions
Lavoisier [late 1700s]:
- the law of conservation of mass
-law of definite proportions
'---> water is always 11% H & 89% O
Proust [1799]:
-if a compund is broken down into its constituents, the products exist in teh same ratio as in the compoun
-experimentally proved Lavoisier Laws
Dalton [early 1800s]
-atoms are solid, indestructible spheres [like Billard Bas]
-provides for different elements (these would be different spheres)
-based on the law of conservation of mass
Haveing a molecule (atoms combine in simple whole number ratios) explains the law of constant composition
If the atoms are not destroyed then the mass does now change
eg.
J.J Thomson [1850s]:
- raisin bun model
- solid, positive spheres, with negative particles embedded in them
- first atomic theory to have positive (protons) & negative (electrons) charge
- demonstrated teh existence of electrons using a cathode ray tube
Rutehrford [1905]:
- showed taht atoms have a positive, dense center with electrons outside it
- resulted in a planetary model
- explains why electrons spin around the nuclues
- suggests atoms are mostly empty space
~christina chow :]
