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400
Democritus
Stated that all matter is composed of tiny indestructible units, called atoms. -
Period: 400 to
History of Atomic Theory
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John Dalton
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.
5) Atoms of different elements combine in simple whole numbers to form compounds Dalton conducted several experiments with gases. These experiments allowed Dalton to form 5 theories. -
Robert Millikan
Stated that the mass of an electron is at least 1000 time smaller than an atom. -
Robert Millikan
Robert Millikan measured the charge on an electron with the apparatus shown. In these experiments, the atomizer from a perfume bottle was used to spray water or oil droplets into a sample chamber. Some of these droplets fell through a pinhole between two plates of an electric field, where they could be observed through a microscope. A source of x-rays was then used to ionize the air in the chamber by removing electrons from the molecules in the air. -
Earnest Rutherford
He stated that the nucleus was small and dense and that only protons and neutrons were located in the nucleus, and electrons orbit around the nucleus.
He conduted the gold foil experiment wich allowed him to make this conclusion. -
Niels Bohr
Created the Bohr model. Bohr was the first to discover that electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of an element. -
Erwin Schrodinger
His experiment helps us find out where the elextron may be.
He conducted a wave equation principal (n), angular (l), and magnetic (m) quantum numbers. These quantum numbers describe the size, shape, and orientation in space of the orbitals on an atom. -
Werner Heisenberg
Created the uncertainty principle states that the position and velocity cannot both be measured,exactly, at the same time. He formed the equation in the following imge. -
James Chadwick
Chadwick determined the velocity of the protons.
He was able to determine that the mass of the neutral radiation was almost exactly the same as that of a proton.
His equation is shown in the image.
