- the four elements theory lasted for about 2000 years
- it is not a scientific theory because it could not be tested against observation
DEMOCRITUS
- in 300 BC Democritus said atoms were indivisible particles
- first mention of atoms (atomos)
- not a testable theory, only a conceptual model
- no mentions 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% Hydrogen and 89% Oxygen
PROUST ( 1799)
- if a compound is broken down into its constituents,
the products exist in the same ration 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 mass
- having a molecule ( atom combine in simple whole number ratios ) explains the law of constant composition
- if the atoms are not destroyed then the mass does not change
J.J THOMSON ( 1850s )
- raisin bun model
- solid, positive spheres, with negative particles embedded in them
- first atomic theory to have positive (protons) and negative (elections) 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.
(This model below was incorrect because electrons would go towards the nucleus oppose to orbiting it. The electrons would move towards the nucleus.)
No comments:
Post a Comment