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Democrtitus
Democrtitus said that all matter consists of extreamly small particles, which can not be seperated what so ever. He called these small things atoms. There is no evidence of experiments. -
Aristotle
Aristotle thought that there was no limit to dividing matter. He developed the theroy that all matter consisted of Earth, Air, Water and Fire. There were also four qualities: dryness, hotness, coldness, and moistness. He made a model, as shown, to explain his theory. -
John Dalton
John Dalton theroized that all atoms of the same elements have the same masses, and atoms of different elemets have different masses. In a particular compound, atoms of differnent elements always combine the same way. He made wooden spheres to show his theory. -
J.J. Thomson
Thompson used electiric currents to learn about atoms. He also did an expeiriment with the seeled tube filled with gas and metal discs to make a glowing beam. This experiment showed that opposite charges attract. He thought that electrons are embeddded in a sphere made of posistive electric charge. -
Max Planck
Planck contibuted to the atomic theory by saying that energy can only be emitted in discrete chunks. His expeirimented by observing light emitted by a heated object at various temperatures. This theory was called the theory of quanta. -
Hantaro Nagaoka
Hantaro Nagaoka predicted that his model had a very massive nucleus and electrons revolving around the nucleus, bound by electrostatic forces. How did he do it? By compairing the model to the planet Saturn. -
Ernest Rutherford
Rutherford explained the atom as having a central positive nucleus surrounded by negative orbiting electrons, in the space around the nucleus. This was a result of his famous gold foil experiment. -
Niel Bohr
Niel Bohr's model was not completely correct, but it had many features that are approximately correct . It said that the electrons move in spherical orbits around the nucleous at fixed speeds and fixed distances. He based this on the planets orbiting aound the sun. -
Erwin Schodinger
Erwin Schodinger described the motion of electrons in atoms by developing mathmatical equations. His work led to the electron cloud model, which is a visual model of the most likely locations for electrons in an atom. -
Henry Moseley
Moseley found a relationship between an element's X-ray wavelength and its atomic number. His discovery showed that atomic numbers had an experimentally measurable basis. He used X-ray wavelengths to help him with the contribution. -
Ernest Marsden
Ernest Mardsen was a student of Ernest Rutherford and with his help performed the gold foil expeiriment. When using all the materials in the right way he discovered that there was a flash of light when struck by a fast moving alpha particle. -
James Chadwick
James Chadwick contibuted to the atomic theory by discovering neutrons that have no charge. The neutrons are joined with the positivly charged protrons while the negative electrons orbit around them. He found out about neutrons by focusing on radioactivity. -
Lois de Broglie
Broglie said that moving particles, such as electrons, could behave as waves under some conditions. This model is similar to the Neil Bohr model. Later, evidence was collected to support this idea.
