Question

why is valence band edge curavture different from conduction band edge curvatures

Answer 1

Valence band is the highest band or energy level in a substance which is partially or fully filled. In case of inert gases, the valence band is full whereas for other materials, it is partially filled. Normally in an atom, valence band has the electrons of highest energy.

Conduction band is the lowest energy band in a substance which is either empty or partially filled by some of the valence electrons at room temperature. In certain materials, such as metals, the valence electrons are loosely attached to their nuclei.Even at ordinary temperature, some of them can jump to conduction band. In fact, this is the process responsible for the conduction of current in a conductor. Moreover, if a substance has empty conduction band , it might be an insulator. On the other hand, conduction band is partially filled for conductors.