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Explain concept of valence band and conduction band in solid crystal. |
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Answer» A. Valence band (V.B): 1. The topmost occupied energy level in an atom is the valence level. The energy band formed by valence energy levels of atoms in a solid is called the valence band. 2. In metallic conductors, the valence electrons are loosely attached to the nucleus. At ordinary room temperature, some valence electrons become free. They do not leave the metal surface but can move from atom to atom randomly. 3. Such free electrons are responsible for electric current through conductors. B. Conduction band (C.B): 1. The immediately next energy level that electrons from valence band can occupy is called conduction level. The band formed by conduction levels is called conduction band. 2. It is the next permitted energy band beyond valence band. 3. In conduction band, electrons move freely and conduct electric current through the solids. 4. An insulator has empty conduction band. |
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