Answer to Question #214962 in Inorganic Chemistry for Calvin

Question

Gallium arsenide has a zinc blende crystal structure. Assume a lattice constant

of a = 5.65 Å. Determine the density of gallium arsenide in g/cm3.

Answer 1

8 atoms per unit cell: 4 Ga and 4 As

atomic weights:

Ga = 69.72 Da or u

As = 74.92

1u = 1.660 ×10−27 kg

Total mass in unit cell: M = 4 × (69.72 + 74.92) ×1.660 ×10−27 kg M = 9.60 ×10−25 kg

Density = mass/volume:

ρ = 9.60 ×10^-25 kg/

(5.65×10^-10 )³

= 5.32 ×10³ kg/m3

(These are proper MKS units. Also called International System of Units (SI).)

ρ = 5.32 ×10³ kg/

m³ ×

10³

gm/

kg

×

1/

10²

( cm/ m)³

= 5.32 gm/cm3

ρ = 5.32 gm/cm3