-
360
Aristotle
Aristotle believed that you would alway's have a smaller peice of matter, regardless of how many times you cut it. -
450
Democritus
First propsed an existence of an "ultimate particle," and he used the word atoms to describe the particles. -
Robert Boyle
Boyle demonstrated the necessity of air for combustion, for animal breathing, and for the transmission of sound. -
Johann Becher and Georg Stahl
Johann Becher and Georg Stahl developed the phlogiston theory between 1670-1790 and, it explained that when something is brned, it lost phlogiston to the air. -
Isaac Newton
Newton's work is the basis of classical mechanics, so it would be used by Dalton and subsequent chemists to develop atomic theory. -
Antoine Lavoisier
Lavoisier propsed the combustion theory which was based on sound mass measuremnets, and he also composed the law of conversation of mass whcih represents the beginning of modern chemistry. -
Joseph Priestly
Joseph Priestly discovered oxygen, which he called "dephlogiticated air." -
Joseph Proust
Joseph Proust composed the law of constant composition. -
John Dalton
John Dalton proposed the law of multiple proportions and, he also proposed different symbols to represent atoms of different elements. -
Joseph Gay-Lussac
Lussac announced the law of combining volumes in 1808 and, he showed that at the same temperature and pressure, two volumes of hydrogen gas reacted with one volume of oxygen gas to produce two volumes of water (as a gas). -
Amadeo Avogadro
Avogadro's hypothsis states that when equal volumes of gases are at the same temprature and pressure, thay contain the same number of molecules or atoms. -
Stanislao Cannizaro
Stanislao Cannizaro said at the Karlsruhe Conference that Avogadro"s hypothsis should be accepted for five years, and a new conference should be called after the five years o discuss any problems. -
Dimitri Mendeleev
Dimitri Mendeleev proposed the periodic law and developed the first periodic table in 1869. -
J.J. Thomson
J.J. Thomson identified the negatively charged electron in the cathode ray tube and, he concluded that the electron was a component of all matter and the calculated the charge to mass ratio for the electron. -
Robert Millikan
Millikan determined the unit charge of the electron, and this allowed the calculation of the mass of the electron and the positively charged atoms. -
Ernest Rutherford
Rutherford proposed the nuclear atom as the result of the gold-foil experiment in 1911, and in 1920, Rutherford he proposed the existence of the third atomic particle, the neutron. -
Henry Moseley
Moseley discovered that the energy of the x-rays emitted by the elements increased in a linear fashion, and the relationship was a function of the positive charge on the nucleas. -
Francis Aston
Francis Aston invented the mass spectrograph. -
James Chadwick
James Chadwick dicovered the neutron.
