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SCIENTIST
Democritus
and the
Greeks 2000
Y.A.
John Dalton
1803
J.J. Thomson
1897
METHOD
CONTRIBUTION
Questioning,
observing, inferring
Hypothesized concept of
atom…ATOMOS = “indivisible”
Experiments with
gases –
Found that gases
were made of
individual particles
Came up w/ ATOMIC THEORY:
1) All elements are made of atoms.
2) Atoms of same element are exactly
alike.
3) Atoms of different elements are
different.
4) Molecules are the result of the
chemical combo of atoms.
 Discovered atom was divisible
Sent electricity
 Contains the ELECTRON
through an uncharged
 Plum Pudding model
gas…
+ - +
– particles came
- + + - +
out!
Ernest
Rutherford
1908
“Shot” + particles
through a piece of
gold foil…some
passed through…
some bounced back
 Discovered center of atom = nucleus
 Nucleus has + charge
 e- are floating in mostly empty space
Niels Bohr
1913
Hypothesized and
built upon work of
Rutherford
 Created the Bohr Model
 Electrons “orbit” nucleus in definite
circles called energy levels.
The Wave
Model
Scientists
TODAY
Worked with
MATHEMATICAL
equations
 Impossible to determine the exact
location of an electron
 Energy of electron at a given time
determines its location
 Opposite of Bohr Model