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Dalton
Solid Sphere Model- Dalton oberseved that elements combine to form compounds and matter is not destroyed or created in chemical reactions. He reasoned elements are made of tiny, invisible spherical particles called atoms. -
Period: to
History of Atomic Theory
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J.J. Thomson
Plum Pudding Model - Thomson zapped atoms with electricity, negative charged particles were removed. He reasoned atoms contained negatively charged electrons. -
Rutherford
Nuclear Model- Rutherford shot tiny positively charged alpha particles at piece of thin gold foil. Most alpha particles went through the foil, but some bounced back. He reasoned there most be a small, dense, positively charged nucleus. -
Bohr
Solar System Model- Bohr developed a model of an atom that explains why light is given off when elements are exposed to flame or electic fields. He reasoned that electrons orbit around the nucleus at different distances and have different energies. His atomic model had atoms built up of sucessive shells of electrons. -
Chadwick
Chadwick found that the nucleus also contained neutrons. He reasoned neutrons helped hold protons together. -
Modern Model
Electron Cloud Model It holds that atoms are a constant. Chemical reactions cannot create, alter or destroy an atom. Atoms can combine to create elements, but the atomic structure of any given element is always the same. Atoms of different elements can combine to create compounds.
