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Democritus’ theory
if matter was broken into smaller pieces you would eventually reach a point where it could not be broken down further
atom atomos
this was rejected by aristotle who favoured empedocles’ 4 elements theory
who were the alchemists
explored the nature of matter
in many cultures
searched for the “elixir of life”
alchemists controbution to atomic theory
technological advances
(lab glassware and equipment, alloys handling procedures for dangerous chemicals)
allowed for the development of modern science
john dalton’s suggestion
atoms are solid spheres like billiard balls
did not address how things acquire electrical charge
john dalton’s suggestion
atoms are solid spheres like billiard balls
did not address how things acquire electrical charge

JJ thomson’s model of the atom
plum pudding
atom is a sphere of uniform positive charge with electrons embedded in it
ernest rutherford’s experiment
gold foil experiment
he bombarded a thin sheet of gold foil with positively
charged alpha particles (a Helium nucleus)
Gold foil experiment expected results
based on Thomson’s model, the alpha particles should
go straight through the gold foil (a uniform “+” charge
isn’t concentrated enough to repel the “+”alpha particles)

Gold foil experiment actual results
almost all the alpha particles did go straight through the
gold foil
about 1 in 20,000 was deflected off course or
rebounded straight back
the alpha particles must have hit something heavy
and positively charged

Ernest Rutherford model of the atom
the nuclear model
Atom has a very small, heavy nucleus surrounded by electrons, most of the atom is empty space