The Development of the Atomic Structures (Theories)

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  • Topic: Atom, Ernest Rutherford, Neutron
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  • Published : November 1, 2012
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Dalton's Model
John Dalton

Five main points of John Dalton's atomic theory
Elements are made of extremely small particles called atoms. •Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties. •Atoms cannot be subdivided, created, or destroyed.

Atoms of different elements combine in simple whole-number ratios to form chemical compounds. •In chemical reactions, atoms are combined, separated, or rearranged.

J.J. Thomson’s Model
J. Jonah Jameson Thomson - (AKA J.J.)

Thomson played with cathode rays. These are just beams of electrons . By having the beam interact with electric and magnetic fields, Thomson was able to determine the mass to charge ratio for an electron. So, from that he knew that the electron came from the atom, it had a negative charge and a small mass. Here is the model that he proposed.

Thomson took the idea of the atom and tried to incorporate the evidence for the electron. In this model, the electrons are the small things and the rest of the stuff is some positive matter. This is commonly called the plum pudding model because the electrons are like things in positive pudding.

Rutherford’s Model
Ernest Rutherford

Along with Hans Geiger and Ernest Marsden in 1909 he carried out the Geiger–Marsden experiment, which demonstrated the nuclear nature of atoms Rutherford was inspired to ask Geiger and Marsden in this experiment to look for alpha particles with very high deflection angles, of a type not expected from any theory of matter at that time. Such deflections, though rare, were found, and proved to be a smooth but high-order function of the deflection angle. It was Rutherford's interpretation of this data that led him to formulate the Rutherford model of the atom in 1911 — that a very small positively charged nucleus was orbited by electrons.

Before leaving Manchester in 1919 to take over the Cavendish...
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