Wednesday, December 17, 2014

JEE Revision - Atomic structure - Basics

Thomson Model

J.J. Thomson studied the properties of cathode rays. Cathode rays were observed in tubes with gas at low pressures when electric charge was applied. The gas starts conducting electricity at low pressure and rays appear. During these studies, Thomson discovered electrons in 1897.

The experiments led to the conclusion that the particles comprising cathode rays were the same irrespective of the material of the cathode and the gas used in discarge tubes, The particles had the same mass and charge. Hence it was concluded that electrons are universal constituents of all matter.

Subsequently proton was also discovered. Rutherford's name can be mentioned in the case of proton as an important researcher.

Thomson proposed that the positive charge is spread over a sphere in which the electrons are embedded. This make the atom neutral. The model was also called Thomson's plum pudding model.

Rutherford model

In 1913, Niels Bohr proposed a model of the atom. He proposed that the electrons in an atom could only be in certain orbits, or energy levels, around the nucleus. Refinement of Bohr theory led to the modern theory of atomic structure based on quantum mechanics.

Wave mechanical model

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