•To some
Greeks, were smallest “indivisible” unit of matter
•In
1700’s, 1800’s discovery of chemical “elements” (H,
He, C, O, N, ...)
somehow made of
different kinds of atoms
•In early
1900’s, parts of atoms and reasons the elements differ understood
•In early to
mid 1900’s ways to change one kind of atom into another understood
–radioactive
decay
–fission
–fusion
–