(a) What are intrinsic semiconductors ? Give an example.
(b) What is the distance between `Na^(+) and CI^(-)` ions in NaCl crystal if tis density is 2.165 g `cm^(-3)` ?
[Atomic Mass of Na = 23u, Cl = 35.5 u, Avogadro's number = `6.023 xx 10^(23)`]

Explanation

(a) Intrinsic semiconductor also called as undoped semiconductors or i-type semiconductor, the number of charge carries is therefore determined by the properties of the material itself instead of the amount of impurities. In intrinsic semiconductors, the number of located electrons and the number of holes are equal N = P.
The most common examples of the intrinsic semiconductors are silicon and germanium. Both of these are used frequently in manufacturing of transistors and electronic products manufacturing.
(b) `d = (Z xx m)/(a^(3) xx N_(A))`
For NaCl = 2.165
`= (4("fcc")xx 58.5)/(a^(3) xx 6.02 xx 10^(23))`
`a^(3) = (4 xx 58.5)/(2.165 xx 6.02 xx 10^(23))`
`= 17.958 xx 10^(-23)`
`a^(3) = 179.58 xx 10^(-24)`
`a = 5.64 xx 10^(-8)`
= 564 pm
We know that
`2(R^(+) + R^(-)) = a`,
Where `R^(+) and R^(-)` are radius of sodium and chlorine ions respectively.
`(R^(+) + R^(-))` is the inter ionic distance
`therefore` Distance between `Na^(+) and Cl^(-)`
`= (564)/(2) = 282` pm