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The atom was believed to be composed of a positively charged nucleus surrounded by negatively charged electrons. In 1932, James Chadwick bombarded beryllium atoms with alpha particles. An unknown radiation was produced.

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The French scientist Henri Becquerel discovered radioactivity in 1896. ... He realized that some invisible radiation had been emitted from the uranium. He won the Nobel Prize in 1903, along with Marie and Pierre Curie, for his discovery, and the SI unit of radioactivity, the becquer (Bq), was named after him.

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He shows that a atom is mostly empty space. He found this discovery out in 1907

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Experiments with gases that first became possible at the turn of the nineteenth century led Dalton to announce his discovery in 1803

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He discovered the electron in 1897. His model mostly contains electrons.

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he was a british chemist and physicist known for his discovery of the element thallium and his studies on the cathode rays which has been fundamental in the development of atomic physics. He found his discovery in 1903.

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Found the nucleus of a atom. He discovered this in 1912.

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Born on 460 BCE. We do not know what date he found his discovery was, the Greek philosopher Democritus suggested that all matter was formed of different types of tiny discrete particles and that the properties of these particles also determined the properties of matter.