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101
Democritus - 429 BC
First person to think of the atom.
Thought atom was a sphere. -
102
Aristotle - 400 BC
He thought that everything was made up of one of the four elements.
He did not believe in atoms. -
Isaac Newton
He believed that there were tiny pieces of mass "swimming" around everywhere. -
John Dalton
He discovered Atomic Theory.
All matter is composed of atoms.
Atoms can be made and destroyed.
All atoms of the same element look the same.
Different atoms have different types of atoms.
Chemical reactions occur when atoms are rearranged.
Compounds are formed from atoms of different elements. -
Henri Becquerel
He helped discover radioactivity. -
J.J. Thomson
He discovered electrons.
Made the "plum pudding" model. -
Robert Millikan
He found the measure of the charge of an electron.
He found the mass of an electron. -
Ernest Rutherford
Found that an atom has a central positive nucleus surrounded by negative orbiting electrons. -
Neils Bohr
He thought that the atom had a small positively charged nucleus with negatively charged surrounding electrons orbiting it. -
Francis Aston
He discovered 212 natural isotopes
He invented the mass spectrometer. -
Erwin Schrondinger
Found that the atom has clouds of energy and that it has a nucleus.
He made an equation to find out where the electron would be in an atom.
He proved the Bohr model incorrect. -
James Chadwick
Discovered that neutrons are congruent to protons in weight.
Discovered the neutron.