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322
322 B.C- Aristotle
Aristotle's Atomic Theory is based on the four elements: earth, wind, fire, and water. According to him, there were 2 forces: conflict and harmony. There were also four properties to describe these: dryness, hotness, coldness, and moistness. -
Period: 400 to
History of the Atomic Theory (and Models)
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460
460 B.C. - Democritus
Democritus' Atomic Theory revolves around all atoms that are present in the atmosphere. These are about all the atoms in all the states of matter (solid, liquid, gas). This theory is simple and easy to understand. -
1800- Dalton
Dalton's Atomic Theory consists of 4 things: 1) All matter is made of atoms. Atoms are invisible 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. -
1897- Thomson
Dalton's Atomic Theory is based on the electron. He discoved this when scientists passed an electric current through a vacummn and could not figure out why a streak of light was left behind, leading dalton to believe there were electricty-carrying particles. -
1911- Rutherford
In his Atomic Theory, Rutherford states that each atom consists of a central nucleus surrounded by circulating electrons. This model suggested that most of the mass of the atom was in the little nucleus. He found this after his famous gold foil experiment, where he fired radioactive particles through a really thin metal sheet, detected by a scintillator. -
1913-Bohr
Bohr applies the quantum theory to Rutherford's idea, stating that particles move in stationary oribits at an angle to each other. This led to the calculation of possible energy levels for these orbits. -
1923- Milikan
Milikan performed an experiment with oil that proved, once and for all, the existence of electrons. By mathmatically calculating the time it took between the affect of gravity and the pull of the electron he measured its voltage. -
1932- Chadwick
Chadwick proved the existence of the neutron through extensive study. His Atomic Theory is based on neutrons, and has greatly improved advances in the nuclear study field of science. -
Most Modern Model of the Atom
The Wave Model is the most recent model of the atom. It states that electrons, although fixed in an orbit, do not move about randomly. It is impossible to determine the exact location of the electron. The possible location of an atom is based on the energy of the electron.
