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460
Democritus
When:460 BC
Where: Greece
What: Democritus and Leucippus' theory stated that everything is composed of atoms, which are physically indivisible; between atoms, there lies empty space; atoms are indestructible; atoms have always been, and will always be in motion; and there are an infinite number of atoms, and kinds of atoms, which differ in shape and size. -
Antoine Levoisier
When: 1778
Where: France
What: Considered to be the father of chemistry, Antoine Lavoisier discovered oxygen in 1778, as well as discovering its role in combustion. -
John Dalton
When: 1803
Where: England
What: John Dalton proposed the Atomic Theory. Which stated: 1. All matter is made of atoms. Atoms are indivisible and indestructible.
2. All atoms of a given element are identical in mass and properties.
3. Compounds are formed by a combination of two or more different kinds of atoms.
4. A chemical reaction is a rearrangement of atoms. -
Dmitri Mendeleev
When: 1869
Where: Russia
What: Created the first version of The Periodic Table of Elements. -
Ernest Rutherford
When: 1871
Where: New Zealand
What: Used the Gold Foil Experiment, which proved that the Atom had a nucleus. Also discovered the proton and also came up with the Rutherford Model. -
Erwin Schrodinger
When: 1887
Where: Austria
What; Contributed to the wave theory of matter and invented the Quantum Mechanical Model of the Atom -
Henry Moseley
When: 1887
Where: United Kingdom
What: Justified that the nucleus contained the same number of positive charges equal to the atom's atomic number. -
J.J. Thompson
When: 1897
Where: England
What: Through his experiments with cathode ray tubes, he showed that cathode rays were composed of electrons, which is why he is credited with the discovery of electrons, and the discovery of the first subatomic particle. Also creator of the Plum Pudding Model. -
Robert A. Millikan
When: 1909
Where: U.S.
What: Used the oil-drop experiment to measure the mass and charge of the electron. -
Electron Cloud
The Electron Cloud Model was created by Erwin Schrodinger and Werner Heisenberg. The Electron Cloud shows where the electrons are as they rotate around the nucleus. The Electron Cloud Model states that electrons don't orbit the nucleus, and we can't know where they are. -
James Chadwick
When: 1932
Where: England
What: Discovered the neutron in the atom's nucleus. -
Niels Bohr
When: 1992
Where: Denmark
What: Suggested that electrons move in an orbit around the nucleus, and contributed the Bohr Planetary Model.
