Question

Magnesium oxide (mgo) has the rock salt crystal structure and a density of 3.58 g/cm3. the atomic weights of magnesium and oxygen are 24.31 g/mol and 16.00 g/mol, respectively. (a) determine the unit cell edge length.

Answer 1

Answer:

(a)  The unit cell edge length 0.421 nm

Explanation:

Lets calculate -:

Given -

density = $3.58g/cm^3$

Molecular weight of MgO = 24.31 +16

                                           $40.13 g/mole$

Avagadro number = $6.022\times10^2^3$

In rock salt structure , there are four anions and four cations , hence Z=4 (Number of formula per unit cell)

Now, using the formula -

                     $d=\frac{ZM}{N_Aa^3}$

               $a=[\frac{ZM}{N_Ad}]]^\frac{1}{3}$

Now, putting the given values

   $a=\frac{4\times40.13g/mole}{6.022\times10^2^3\times(3.58g/cm^3)}$

  $4.21\times10^-^8 cm$

  = 0.421 nm

Hence , the unit cell edge length = 0.421 nm