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400
Democritus
He expressed that matter was composed of small atoms that could be divided no further. The atoms were all composed of the same primary matter with the weight, size, and shape being the only difference. -
Period: 400 to
Atom Timeline
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Antonie L.
He stated that matter can be neither created nor destroyed in a chemical reaction, and the differences in elements and compounds. -
Joseph Preistly
discovered oxygen -
Joseph Proust
He disapproved Berthollet with the law of definite proportions. He showed that no intermediate indeterminate compounds existed between them. -
J Dalton
1) matter composed of small atoms 2) all atoms of an element are identical, but different from those of any other element 3) during a chemical reactions atoms are neither created nor destroyed, but rearranged 4) atoms always combine in whole numbers multiples of each other. -
Dmitri Mendellev
He created the first periodic table then he went on to make predictions about the properties of missing elements. -
Henri Becquerel
He discovered that a sample of uranium was able to expose a photographic plate even when the sample and plate were separated. Exposure of the plate did not depend on the chemical state of cranium and therefore must be due to some property of uranium atom itself. -
Marie Curie
Atoms might be composed of even smaller particles and might have a structure that could be analyzed. -
JJ Thomson
Since atoms were electrically neutral, the atom must also contain a positive charge. An atom was composed of a spherical ball of positive charge imbedded in it. -
Ernest Rutherford
He discoverd positive particles and lighter mass and negative particles, radiation emitted from uranium was composed of two elements. -
Max Planck
He introduced the quantim theory. -
Rutherford, Han Geiger
They discovered that a large comcentration of charge was located at the center of an atom and became known as the nucleus. -
Robert Millikan
Mass of an electron was calculated for the first time. -
Henry Moseley
"There is in the atom a fundamental quantity, which increases by regular steps as we pass from one element to the next", "quantity can only be the charge on the central positive nucleus". -
Bohr
The theory that electrons travel in discrete orbits around the atoms nucleus. -
Louis de Broglie
He discovered electron waves, only moving particles or objects had an associated wave. -
Erwin S.
Example of his EquationSchrodinger equation describes how the quantum state of a physical system changes. -
James Cadwick
He identified the neutron.
