Atoms are spheres and each element has a different type of sphere
JJ Thomson (1897-1906)
Came up with plum pudding model
Used cathode rays (streams of particles) to discover electrons
Discovered atoms aren't solid and made up of other particles
Ernest Rutherford (1909)
Came up with nuclear model
Discovered the nucleus
Nucleus is very small, dense and positively charged
Atom is mainly empty-spaced and made up of a negative cloud
Gold leaf experiment
Positive alpha particles fired at thin gold foil
Most went through gold leaf (mainly empty spaced)
Some deflected back (small positive nucleus)
Niels Bohr (1913)
Electrons must exist in fixed energy levels so atom doesn't collapse towards positive nucleus
Came up with atomic model
The Experimental Proof
Electrons move up to higher energy levels when EM radiation is absorbed AND electrons move down to lower energy levels when this EM radiation is released
James Chadwick (1932)
Discovered the neutron
Atomic Model today
Electrons do NOT have the same energy in shells
Electrons orbit nucleus in sub-shells, which explains ionisation trends
