1.

Derive the expression to calculate density of unit cell.

Answer»

Solution : LET the edge length of unit cell = a pm
`therefore`VOLUME of unit cell `= a^3 xx 10^(-30) cm^3`
Let the no. of atoms persent per unit cell - Z
HENCE, the mass of ATOM `(m) = (M)/(N_A)` present in unit cell .
M = MOLAR mass, `N_A` = Avogadro.s number
The total mass of unit cell = `(Z xx M)/(N_A)`
The density of a unit cell is given by
d = `("Total mass of unit cell")/("Total volume of unit cell")`
`d = (Z xx M)/(N_A xx a^3 xx 10^(-30)) g/(cm^3)`.


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