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300
Aristotle (384-322 BC)
Aristotle believed in the four elements of air, earth, water and fire. Aristotle felt that regardless of the number of times you cut a form of matter in half, you would always have a smaller piece of that matter. This view held sway for 2000 years primarily because Aristotle was the tutor of Alexander the Great. -
400
Democritus (460-370 BC)
Democritus first proposed the existence of an ultimate particle. Used the word "atomos" to describe this particle. -
John Dalton (1776-1844)
Dalton proposed the Law of Multiple Proportions and developed the concept of the mole and proposed a system of symbols to represent atoms of different elements. Dalton recognized the existence of atoms of elements and that compounds formed from the union of these atoms. He therefore assumed that simplest ratios would be used in nature and came up with a formula for water of HO. He then assigned a relative atomic weight of one to hydrogen and developed a relative atomic weight scale from perce -
Max Planck
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Robert Milikah (1868-1953)
Millikan determined the unit charge of the electron in 1909 with his oil drop experiment. Thus allowing for the calculation of the mass of the electron and the positively charged atoms.
e = 1.60 x 10-19 coulombs -
Niels Bohr
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Louis deBroglie
His ideas were a basis for developing the wave mechanics theory. This theory has greatly improved our knowledge of the physical nature on the atomic scale. -
Werner Hesienberg
Werner's contribution to the atomic theory was that he calculated the behavior of electrons, and subatomic particles that also make up an atom. Instead of focusing mainly on scientific terms, this idea brought mathematics more into understanding the patterns of an atom's electrons. Werner's discovery 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. Surro -
Erwin Schrodinger
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James Chadwick (1891-1974)
Chadwick discovered the neutron in 1932. Chadwick was a collaborator of Rutherford's. Interestingly, the discovery of the neutron led directly to the discovery of fission and ultimately to the atomic bomb. -
Joseph John Thomson (1856-1940)
Thomson proposed the "plum pudding" model of the atom. In this model, the volume of the atom is composed primarily of the more massive (thus larger) positive portion (the plum pudding). The smaller electrons (actually, raisins in the plum pudding ) are dispersed throughout the positive mass to maintain charge neutrality.
This is the plum pudding model in a watermelon the Seeds representing the smaller electrons -
Ernest Rutherford (1871-1937)
Rutherford proposed the nuclear atom as the result of the gold-foil experiment in 1911. Rutherford proposed that all of the positive charge and all of the mass of the atom occupied a small volume at the center of the atom and that most of the volume of the atom was empty space occupied by the electrons. Although positive particles had been discussed for some time, Rutherford in 1920 that first referred to the hydrogen nucleus as a proton. Rutherford proposed the existence of the the neutron
