History of the Atom: Early ideas of matter: Greek Philosophers: Aristotle (384-322 B.C.) four elements: Fire, Air, Earth, Water

Democritus (460-370 B.C.) Matter is make of small, solid objects that cannot be divided, created or destroyed Atoms are constantly moving Different types of matter are made of different types of atoms Properties of the atoms determine the properties of the matter

Dalton’s Model Matter is made of atoms that cannot be divided, created or destroyed During a reaction atoms of one element cannot be converted into atoms of another element Atoms of one element are identical to each other but different from atoms of another element Atoms combine in a specific ratio

Thomson 1856-1940 Cathode ray tubes: greenish-colored rays travelled from one electrode to the other end Added charged plate in the middle and the ray bent away from negative charge. Concluded: Cathode rays are negatively charged - Electrons

Thomson’s model

Atoms are mostly empty space (Rutherford, 1871-1937) He shot alpha particles through gold foil and 99% of the particles when right through.

Thomson VS. Rutherford

Bohr model 1885-1962 Bohr propsed that electrons are circling the positive nucleus and the farther the

Lewis Dot Structures