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Isaac Newton
Formulated the theory of light, the three laws of motion and suggested a mechanical universe with small solid masses in motion. He said that atoms were held together by forces. -
John Dalton
Daltons atomic theory suggested that all matter was made of atoms, all atoms of a given element are identical, compounds are formed when two or more kinds of atoms combine, and taht a chemical reaction is a rearrangement of atoms. His theroy still holds true today. -
Dimitri Mendeleev
Best known for his work on the periodic table. He arranged 63 known elements into a periodic table based on atomic mass. He left space for new elements and didnt have any of teh noble gasses for they had not been discovered. -
JJ Thomson
Discovered the electron in 1879, he figured out atoms were made up of smaller particles, thus the electron. Thomson discovered the electron and it was proved that atoms were made of electrons, protons, and neutrons, proving that atoms were divisble. Since the atom was neutral, he suggested that the negatively charged electron was equalled by a positively charged protons and neutrons had no charge, he suggested to consider that atoms were spheres. -
Marie Curie
Studied uranium and thorium decay to discover radioactivity. Also later discovered polonium and radium. -
Ernest Rutherford
Describes the atom as having a central posistive necleus that is surrounded by negative obiting electrons. This suggested that that mass of the atom was contained within the small nucleus and teh rest was mostly empty space. -
R.A. Millikan
He determined the charge and mass of an electron by his famous "oil drop" experiment. -
Hans Geiger
Came across his theory in 1912, that in any atom the nucleus occupies a very small volume at the centre. By using a machine called the "Geiger Counter" he created to count the number of alpha particles and other ionising radiation. -
H.G. Moseley
Using x-ray tubes, determined the charges on the nuclei of most atoms. He wrote the atomic number of an element is equvalent to the number of protons in the nucleus. This was used to reorganize the periodic table based on atomic number verses atomic mass. -
Niels Bohr
Built the first model of the atom. He explained that emission and absorption of radiation as transistions between stationary electronis states that eceltrons orbit the nucleus at a fixed distance. -
Werner Heisenberg
He attended the University of Munich, in Germany, to study physics. Using his knowledge, he created Matrix mechanics, the first version of quantum mechanics 1925. One of his most memorible discoveries is the uncertainty principle. He said this means that electrons do not travel in neat orbits. -
James Chadwick
In 1932, Chadwick proved the exsistence of neutrons. He stated that neutrons hel to stabilize the protons in the atoms nucleus, the nucleus is so tightky packed together that the posistively charged protons would tend to repel each other. Neutrons hel reduce the repulsion between the protons to stabilixe the nucleus. Neutrons are always in the atoms nucleus, they are about the same size as the protons. -
Lise Meitner
Did expeirements that proved that heavy elements capture neutrons and form unstable products which inturn undergo fission. This ejects more neutrons while continuing the fission chain reactions. -
Democritus
Worked with Leucippus to express a theory that atsated that everything was composed of "Atoms." They reasoned that the soldiness of a material directly related to the shape of the atoms it was made of. Using analogies from "sense expirements" he gave an image of an atom that distingushied them from others due to their shape, size, and arragement of parts.
