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MORE ON DEMOCRITUS He came up with the term “atom” He thought atoms had different shapes
and sizes He thought they were indivisible and
indestructible “atomists” – people who followed his
beliefs
ARISTOTLE (GREEK~350 B.C.) His beliefs were more likethe early Greeks Philosopher
Atoms? Give me a break! I could speak for hours
against their existence.
JOHN DALTON (ENGLAND~1800)
Dalton’s Atomic TheoryMatter is composed of atomsAll atoms of the same element are identical;
different elements have unique atomsThey cannot be destroyed or createdThey combine to form compounds
JJ THOMSON (ENGLAND – 1897) Discovered the electron Proved the atom can be divided Plum pudding model
MASS NUMBER The number of protons and neutrons The “rounded” number Neutrons = mass number – atomic
number Isotopes – atoms possessing the same
number of protons but different neutrons