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400 B.C.
Democritus was the first to identify the possibility of an atom, which would be the smallest piece of matter
He theorized that atoms are inpenetrable and have a density proportionate to their volume -
The only amplification of the identification of atoms until 1793 would be in 300 B.C. by a man named Aristotle
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1793- John Dalton wrote a book called, “Meteorological Observations.” This book assisted people in discovery types of atoms through meteorology. Dalton also claimed that the forces of repulsion thought to cause pressure acted only between two atoms of the same kind and that a mixture of atoms were indeed different weight and a “complexity.”
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1808-1827
Dalton expressed his other discoveries about atomic mass in his New System of Chemical Philosophy. -
In 1897, Thomson showed that cathode rays were composed of previously unknown negatively charged particles. Because of him finding smaller particles than atoms, he discovered the identification of electrons. Thomson is also credited with finding stable isotopes in 1913
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In 1909 Milliken started to determine the electric charge carried by a single electron. In 1910 his “oil-drop experiment” because widely famous.
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Know as “ The father of nuclear physics.” In 1911, although he could not prove that it was positive or negative, he theorized that atoms have their charge concentrated in a very small nucleus, and thereby pioneered the Rutherford model of the atom, through his discovery.
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Rutherford is also widely credited with “splitting the first atom” in 1917 in a nuclear reaction.
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Bohr developed the Bohr model of the atom, in which he proposed that energy levels of electrons are discrete and that the electrons revolve in stable orbits around the atomic nucleus. In 1922, Bohr received the Nobel Prize in Physics.
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(Biggest Achievement- In 1923 he won a Nobel Prize for Physics for his measurement of the elementary electronic charge and for his work on the photoeletric effect)
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Chadwick discovered the neutron and was later awarded the Nobel Prize in 1935
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In 1941, he wrote the final draft of the MAUD Report, which inspired the U.S. government to begin serious atomic bomb research efforts. He was head of the team that worked on the Manhattan Project. Chadwick went on to measure a nuetrons mass.
