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Explain with a suitable diagram the concepts of valence band and conduction band. |
Answer» Solution :A crystal consists of a three dimensional periodically repeating arrangement of a large number, say N, of the atoms, ions or molecules of the solid. An isolated atom is characterized by discrete and well-defined allowed electron energy levels. As the atomns come close together in a solid, for each of the discrete energy level of an atom, there are N such levels in the crystal. The energies of these N levels DIFFER so slightly that theirdistribution is very nearly continuous and said to CONSTITUTE an energy bands energies are FORMED which the electrons may occupy. These bands are separated bybands of forbidden energies.  The energy levels of inner shell electrons are not affected much by thepresence of neighbouring atoms and hardly widen into bands. They play no part in determiningthe electrical properties of solids The TWO energy bands which are important for electrical conduction a crystal are the highest almost-filled band and the lowest almost-empyt band, respectively called the valence and conduction bands. At or see absolute zero of TEMPERATURE, the energy band whose all available states a occupied by valence electrons is called the valence band while the empyt electrical properties of solids. energy band above it is called the conduction band. |
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