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445 BCE
Democritus
Was the first to propose an atomic universe. -
335 BCE
Aristotle
Aristotle founded his own school, where he tought, studyed and wrote. Said there was no atom -
Antonie Lavosier
Compiled a list of 23 elements -
Joseph Proust
First to publish the Law of Definite Proportions -
John Dalton
pioneer in the development of modern atomic theory. -
Amedeo Avagadro
Determine the volume of 1 mole of gas; base unit to measure the amount of a substance -
William Crookes
know for his cathode-ray studies, fundamental in the development of atomic physics. -
Henri Becquerel
Discovered that phosphorescent and uranium salts when not exposed to light produced spontaneous emissions that darkened photographic plates -
Madame Curie
The rays and particles emitted by a radioactive source are called radiation -
J.J. Thomson
discovered the electron by experimenting with a Crookes, or cathode ray, tube. -
Albert Einstein
a photon is a particle of electromagnetic radiation with no mass that carries a quantum of energy -
Ernest Rutherford
overturned Thomson's model in 1911 with his well-known gold foil experiment in which he demonstrated that the atom has a tiny, heavy nucleus -
Robert Millikan
His oil drop experiment helped to quantify the charge of an electron, which contributed greatly to our understanding of the structure of the atom -
Henry Moseley
Discovered that each element had a certain number of protons and electrons called the atomic number -
Niels Bohr
Made an atomic model of a hydrogen atom to try and figure how to measure energy in an atom -
Max Planck
Discovered that each element had a certain number of protons and electrons called the atomic number -
Erwin Schrodinger
Came up with a new model for the hydrogen atom: the quantum mechanical model -
Werner Heisenberg
Came up with the Heisenberg uncertainty principle which states that it is fundamentally impossible to know precisely both the velocity and position of a particle at the same time -
Louis deBroglie
Came up with the deBroglie equation: wavelength = h/mv (m=mass, v=velocity) -
James Chadwick
Showed that the nucleus contained subatomic particle called a neutron