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Antoine Lavoisier 1783
He invented the analytical balance and showed that chemical elements were neither created nor destroyed, Also he discovered that water is made of hydrogen and oxygen -
John Dalton 1803
Believed the atom was based on measureable properties of mass. -
Henri Becquerel 1896
While he was studying the effect of x-rays on photographic film, he stumbled into some chemicals that would spontaneously decompose and give off pentrating rays. -
J.J Thompson 1897
Studied "canal rays" and discovered that they were associated with the proton H + . he also discovered the mass ratio -
Marie & Pierre Curie 1898
Marie introduced the theory of radioactivity. Marie and Pierre discovered the radioactive elements Polonium and Radium. -
Max Planck 1900
Explained hot glowing matter using quanta. -
Robert Millikan 1909
He discovered the charge and mass of an electron by doing an oil drop experiment charge=(e=1.602 x 10 -19 coulomb) and the mass=(m = 9.11 x 10 -28 gram). -
Ernest Ruthorford 1911
He discovered that the nucleus was very dense,very small and had a positive charge. He also assumed that the electrons were located outside the nucleus, he later on was proved to be correct. -
Henry Moseley 1914
He wrote "The atomic number of an element is equal to the number of protons in the nucleus". This later on became the structure of the periodic table instead of atomic mass. -
Niels Bohr 1922
Proposed a theory of the atomc structure, by using the periodic table. Introduced the theory that electrons orbit around the nucleus of an atom. -
Erwin Schrodinger 1926
Believed that the atom was only made of waves, but not particles. -
Werner Heisenberg 1927
Proposed Principle of Indeterminancy - you can not know both the position and velocity of a particle. -
James Chadwick 1932
Discovered the neutron, which he realized had a mass that was close to a proton -
Democritus 400 B.C
Believed atoms could be any size and that they were induvidually created and couldn't be seperated. -
Aristotle 400 B.C
Aristotle believed that the atom was made from the portions of the four elements; water, fire, wind, and earth. He didn't believe that there wasn't a "smallest' part of matter.
