Explain energy bands in solids
Answers
Electronics devices and circuits >> Atomic physics >> Energy band theory in solids
Energy band theory in solids
In a single isolated atom, the electrons in each orbit have definite energy associated with it. But in case of solids all the atoms are close to each other, so the energy levels of outermost orbit electrons are affected by the neighboring atoms.
When two single or isolated atoms are bring close to each other then the outermost orbit electrons of two atoms are interact or shared with each other. i.e, the electrons in the outermost orbit of one atom experience a attractive force from the nearest or neighboring atomic nucleus. Due to this the energies of the electrons will not be in same level, the energy levels of electrons are changed to a value which is higher or lower than that of the original energy level of the electron.
The electrons in same orbit exhibits different energy levels. The grouping of this different energy levels is called energy band.
However, the energy levels of inner orbit electrons are not much affected by the presence of neighboring atoms.
Important energy bands in solids
There are number of energy bands in solids but three of them are very important. These three energy bands are important to understand the behavior of solids. These energy bands are
Valence band
Conduction band
Forbidden band or forbidden gap
Energy band theory in solids
Valence band
The energy band which is formed by grouping the range of energy levels of the valence electrons or outermost orbit electrons is called as valence band.
Valence band is present below the conduction band as shown in figure. Electrons in the valence band have lower energy than the electrons in conduction band.
The electrons present in the valence band are loosely bound to the nucleus of atom.
Conduction band
The energy band which is formed by grouping the range of energy levels of the free electrons is called as conduction band.
Generally, the conduction band is empty but when external energy is applied the electrons in the valence band jumps in to the conduction band and becomes free electrons. Electrons in the conduction band have higher energy than the electrons in valence band.
The conduction band electrons are not bound to the nucleus of atom.
Forbidden gap
The energy gap which is present between the valence band and conduction band by separating these two energy bands is called as forbidden band or forbidden gap.
In solids, electrons cannot stay in forbidden gap because there is no allowed energy state in this region. Forbidden gap is the major factor for determining the electrical conductivity of a solid. The classification of materials as insulators, conductors and semiconductors is mainly depends on forbidden gap.
The energy associated with forbidden band is called energy gap and it is measured in unit electron volt (eV).
1 eV = 1.6 × 10-19 J
The applied external energy in the form of heat or light must be equal to to the forbidden gap in order to push an electron from valence band to the conduction band.
Answer:
an atom which is so far removed from other atoms as not be affected at all by their electric field is called isolated atom
Explanation:
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