Download Democritus (460 BC-350BC) was a Greek philosopher who thought

Democritus (460 BC-350BC) was a
Greek philosopher who thought that
all matter was made of tiny
indivisible particles he called
atomos.
John Dalton, in the early 1800’s, gave
us his version of the atomic theory.
J.J. Thomson, a physicist, did a
series of experiments with cathode
ray tubes that proved the existence
of the electron.
Thomson continued to experiment
and postulated that the atom
looked like plum pudding (think
chocolate chip cookie) with
protons and electrons in it.
Ernest Rutherford was a student of
Thomson and wanted to learn
more. He conducted the gold foil
experiment and found the
existence of the dense, positively
charged nucleus.
Niels Bohr worked with Rutherford
and went one step further. He said
the electrons were located in
energy levels and gave us the
planetary model.
We progressed beyond the Bohr
planetary model to today’s model
– one in which electrons are at
specific energy levels but are
known to always be in motion and
not orbiting the nucleus.