The Atom Democritus Atom cant cut Aristotle Hyle

The Atom

§ § Democritus. A-tom: can’t cut Aristotle Hyle - continuous material, can always cut.

1700’s § § Law of Conservation of Mass mass is neither created nor destroyed. Law of Definite Proportions Compounds contain the same elements in exactly the same proportions. § Law of Multiple Proportions § Compounds of the same elements contain ratios of masses in small whole numbers.

Dalton - An 1808 school teacher 1. All matter is composed of extremely small particles called atoms. 2. Atoms of a given element are identical in size, mass and other properties. 3. Atoms cannot be subdivided, created or destroyed. 4. Atoms of different elements combine in simple whole number ratios. 5. In Chem Rxns, atoms are combined, separated, or rearranged.

Dalton

Cathode ray tubes cathode

Cathode ray tubes cathode anode +

Cathode ray tubes anode cathode + +

Cathode ray tubes cathode

Cathode ray tubes anode cathode + +

Cathode ray tubes anode cathode + +

Cathode ray tubes anode cathode + +

JJ Thomson (1897) § Concluded that atoms were made of electrons which carry a negative charge and have very little mass.

Dalton’s atom Thomson’s atom - - -Solid ball Ball with many floating Electrons(plum pudding)

Millikan § Used atomizer and charged oil droplets to determine the mass and the charge of electrons +. . . -

Rutherford §. .

Rutherford §.

Rutherford § Determined that since the positively charged radiation particles were only sometimes being deflected, that there must be a very small area of very dense positively charged particles in the center of the atom NUCLEUS.

Dalton’s atom Thomson’s atom - - -Solid ball Ball with many floating electrons

§ Volume of the nucleus is very small with respect to the overall atomic volume. § Electrons surround the nucleus in “orbits” like planets surrounded the sun.

§ Solar system § How do the protons stay together in the nucleus? § What about neutrons? § Bohr