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400
Aristotle (384-322 BC)
Aristotle believed that all things were made up of four simple elements, fire, air, earth, and water. This theory was proposed around 400 BC. This model was adopted because nobody had such a well thought out explaination. Aristotle believes that all atoms were made up of the four simple elements. (fire, air, water, and earth) -
John Dalton (1766-1844)
Dalton's theory remains valid. Today we know that atoms can be destroyed by using nuclear reactions but not chemical reactions. He was studying the study of color blindness. -
Henri Becquerel (1852-1908)
While studying the aftereffects of x-rays on a photograph film, Henri discovered some chemicals randomly breakdown and give off very peircing rays. -
Marie Curie
Studied uranium and thorium and called their random decomposing theory of "radioactivity". Her husband Pierre also discovered the radioactive elements polonium and radium. Coming to their theory of the atom overcoming Chadwicks and others. -
Niels Bohr (1885 - 1962)
Niels Bohr was born on October 7, 1885 in Copenhagen, Denmark. Niels atomic model had atoms built together with repetitive orbital shells of electrons. He compared it to the solar system, and that is why people believed it. -
James Chadwick (1891 - 1974)
James Chadwick was born in Cheshire, England, on 20th October, 1891. Using alpha particles he discovered a neutral particle with a mass very close to a proton. This was the discovering of the neutron. He later won a Nobel Prize for Physics in 1935. -
Democritus (460-370 BC)
He dedicated the belief in Zeus and other greek gods to the men incomprehension of meteorological and astronomical studies. Democritus didnt start the atomic theory, he learned it from its creator, Leucippus. -
J.J Thompson (1856 - 1940)
in 1897 in Cambridge, J J Thomson experimented on cathode rays. Physicists had fought over if these rays were particles, but other physicists thought differnet, thinking they were a type of electromagnetic radiation. Thomson showed that cathode rays were little particles with a negative electric charge and much smaller than an atom. He also thought all atoms contained them.
