1. Tardigrade
  2. Question
  3. Physics
  4. Consider four statements. I. Inside crystal, because of difference of position, each electron has different energy; this makes energy bands in crystals. II. Energy levels of valence electrons are included in valence band. III. Energy level above the valence band is conduction band. IV. In metals, conduction band and valence band overlap. Correct statements are

Q. Consider four statements.
I. Inside crystal, because of difference of position, each electron has different energy; this makes energy bands in crystals.
II. Energy levels of valence electrons are included in valence band.
III. Energy level above the valence band is conduction band.
IV. In metals, conduction band and valence band overlap. Correct statements are

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Solution:

In a solid, electron's energies are very different from that in an isolated atom. Inside the crystal, each electron has a unique position and no two electrons see exactly the same pattern of surrounding charges. Because of this, each electron will have a different energy level.
These different energy levels with continuous energy variation form what are called energy bands. The energy band which includes the energy levels of the valence electrons is called the valence band. The energy band above the valence band is called the conduction band.
Some electrons from the valence band may gain external energy to cross the gap between the conduction band and the valence band. Then, these electrons will move into the conduction band.
At the same time they will create vacant energy levels in the valence band where other valence electrons can move. Thus, the process creates the possibility of conduction due to electrons in conduction band as well as due to vacancies in the valence band. In metals, conduction band and valence band overlap.