# Answer on Atomic and Nuclear Physics Question for Tahir Ahmad khan

Question #49856

reasons that why the electrons cannot reside in energy gap or forbidden band gap?

Expert's answer

From quantum mechanics we know that electrons in isolated atom cannot reside anywhere between allowed discrete

energy levels. This is the origin of energy gap.

Quantum theory shows that when two atomsare brought close enough together to interact, each of the allowed electron

energy levels within the atoms splits into two distinct but closely spaced

energy levels as the atoms combine to form the two-atom system. In a six-atom system, each allowed electronenergy level is split into a set of six separate but closely spaced energy

levels. Clearly then, as we pack moreand more atoms closely together each set of split energy levels contains more

and more levels spread over the same energy range allowed at that particular

radius from the nuclei. So, in a crystallinesolid, such as a metal or a diamond, where billions upon billions of atoms are

packed closely together, the energy levels within each set become so closely

spaced in energy that they form a practically continuous energy band.

The forbidden band gap corresponds to thegaps between electron energy levels within the isolated atoms.

energy levels. This is the origin of energy gap.

Quantum theory shows that when two atomsare brought close enough together to interact, each of the allowed electron

energy levels within the atoms splits into two distinct but closely spaced

energy levels as the atoms combine to form the two-atom system. In a six-atom system, each allowed electronenergy level is split into a set of six separate but closely spaced energy

levels. Clearly then, as we pack moreand more atoms closely together each set of split energy levels contains more

and more levels spread over the same energy range allowed at that particular

radius from the nuclei. So, in a crystallinesolid, such as a metal or a diamond, where billions upon billions of atoms are

packed closely together, the energy levels within each set become so closely

spaced in energy that they form a practically continuous energy band.

The forbidden band gap corresponds to thegaps between electron energy levels within the isolated atoms.

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