Question

3. Why does w
4. Derive an expression for calculation of density of a cubic crystal of an element whose edge is
'a' pm and atomic mass M​

Answer 1

Expression for calculation of density of a cubic crystal of an element whose edge is 'a' pm and atomic mass M is -

• Given - Edge of a cubic crystal unit cell = a pm

Atomic mass = M

• Let number of atom's present per unit cell = Z

and Volume of unit cell = a³ Pm³.

• As , we know Density = Mass/ Volume
• Density of unit cell =

Mass of unit cell / volume of unit cell.

• so, Mass of unit cell = Mass of each atom * no. of atoms present per unit cell . = m * Z

• Mass of each atom =Atomic mass

Avagadro no.

=M/NA

• As, we know all the values so by substituting them we can get the expression for density.

• so, Density of unit cell = atomic mass *no of

atoms per unit cell

Avagadro no. *

Volume of unit cell

• D = M *Z/NA*a³ g/pm³
• D= M*Z/NA*a³*10-30 g/cm³ (1pm=10-10cm)