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101
Democritus - 429 BC
First person to think of the atom.
Thought atom was solid sphere. -
120
Aristotle - 400 BC
Everything made up of fire, earth, air, and water -
Isaac Newton
Tiny pieces of mass swimming everywhere. -
John Dalton
Atomic Theory:
1) All matter is composed of atoms. True
2) Atoms cannot be made or destroyed. False
3) All atoms of the same element are identical. False
4) Different elements have different types of atoms. True
5) Chemical reactions occur when atoms are rearranged. True
6) Compounds are formed from atoms of different elements. True -
Henri Becquerel
Helped discover radioactivity. -
Joseph John Thomson
Proved negatively charged particles. (Electrons) -
Robert Millikan
Measured charge and mass of an electron. -
Rutherford
Atom has a central positive nucleus surrounded by negative orbiting electrons -
Neils Bohr
Atoms are small positively charged nucleus surrounded by electrons traveling in circular orbit -
Francis Aston
Isotopes of non-radioactive elements
212 natural atoms -
Erwin
Nucleus and shells
Each shell contains subshells -
James Chadwick
Discovered Neutron