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384 BCE
Aristotle
Didn't believe in atomic theory. Thought everything was made up of the 4 'elements', fire, earth, water and air. -
350 BCE
Democritus
Mentor was named Leucippus who had come up with atomic theory. Democritus adopted it and came up with the fact that atoms were indivisible. -
Period: 322 BCE to
Key scientist timeline
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John Dalton
3 parts to his atomic theory
-All mater is made up of atoms
-Atoms are indivisible and indestructible
-Compounds are formed by two or more different kinds of atoms -
J.J Thomson
-Discovered the electron and it's negative charge
- Discovered that there should have been positive charge in the nucleus to attract the electrons. -
Philipp Lenard
Described atoms as mostly empty space that are filled with fast moving dynamides
Neutrally charged particles made up of heavy positive particles stuck to a light negative particle -
Ernest Rutherford
-Performed an experiment where he fired positively charged alpha particles at a piece of gold foil
- Found that a small number bounced back.
-Found atoms were made up of a positively charged nucleus orbited by electrons. -
Niels Bohr
Changed Rutherford's model and proposed that electrons can only travel in certain orbits. -
James Chadwick
Discovered the nucleus was made up of neutrons and protons
