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400
Democritus Theory
(Approximate date 400 B.C) Democritus believed that atoms were small hard particles made out of one single material formed into different sixes and shapes. He thought that if you cut particles small enough you would eventually end up with a particle that could not be cut. He called this the atom. -
John Dalton Theory
Dalton discovered that all matter is made up of atoms. Atoms can not be destoryed. When atoms are rearranged it is a chemical reaction. All atoms of a given element are identical in mass and properties, compounds are formed by a combination of two or more different kinds of atoms. Daltons model of atoms was tiny and indivisible. Atoms were indestructible and each one had a certain mass, size, and chemical behavior that was determined by the element they were. -
J.J Thomson Theory
Thomson discovered the electron. His model is called the "plum-pudding model". It is called so because it showed an atom as having negatively charged electrons clumped into a positively charged rest of the atom, which appeared to look like plum-pudding. -
Ernest Rutherford Theory
Rutherford conducted a Geiger–Marsden (Gold Foil) experiment and discovered that atoms were mostly empty space. The experimetn also disproved Thomson's plum-pudding theory.The Rutherford Model was very tiny and it showed an atom as having a central nucleus that contained most of the atom's massand electrons in the empty space surrounding the nucleus. Thomson's model was diffrent because it showed atoms as having empty space instead of being mushed so close together. -
Neils Bohr Theory
Bohr's model was called the Bohr model. It showed that ectrons travel around the atom in discrete orbits and that they can switch between orbits, in the process emitting a photon. This later became the basis for the quantam theory. Bohr's theory was different than Rutherfords because it showed that electrons have definitive orbits that they follow. -
Louis de Broglie Theory
De Brogile contributed to the atomic theory by stating that all moving particles, ecspecially sub atomic particles-, show a degree of wavelike behavior. -
James Chadwick Theory
Chadwick discovered that there are neutrons in an atom.This later led to the creation of the atomic bomb. It also changed the atomic model by showing the neutrons in the nucleus of an atom. His model was different than the otherss before it because it included neutrons in its nucleus. -
Werner Heisenberg Theory
Heisenberg discovered that electrons do not travel in neat orbits. He calculated the behavior of electrons, and subatomic particles that also make up an atom. Heisenberg helped clarify the modern view of the atom because scientists can compare the actually few numbers of atoms there are, by their movements of electrons, and how many electrons an atom contains. -
Modern Atomic Theory
The atomic theory that is believed today is a combination of the atomic theorys of the past. Our modern theory states that atoms are mostly empty space, but have a nucleus that contains most of the atom's mass. Weknow this because of Rutherford's Gold Foil experiment. We also know that electrons are apart of atoms due to Thomson's discovery, neutrons are in an atoms nucleus, due to Chadwick's discovery, and protons. We know that electrons follow orbits due to Bohr's discovery. -
Robert Millikan Theory
Millikan determined the unit charge of the electron with his oil drop experiment allowing for the calculation of the mass of the electron and the positively charged atoms.
