The Solid State

• Question 37

## How many atoms can be assigned to its unit cell if an element forms (i) a body centred cubic cell and (ii) a face centred cubic cell?

Solution
(i) for a body centred cubic cell 2 atoms.
(ii)for  face centred cubic cell 4 atoms.
Question 38

## How many Ca+ ions occupy second nearest neighbour locations to a central Cs+ ion in caesium chloride crystal?

Solution
Co-ordination number of Cs+ ion is 8 in the crystal of caesium chloride .
Question 39

## How many Na+ ions occupy second nearest neighbour locations of a Na+ ion in the structure of sodium chloride crystals?

Solution
The second nearest Co-ordination number of Na+ ions is 12.
Question 40

## Why FeO is non-stoichiometric with the formula Fe0.95 O explain?

Solution
The non-stoichiometry reflect the ease of oxidation of Fe2+ to Fe3+ effectively replacing a small portion of Fe2+ with two thirds their number of Fe3+. Thus for every three 'missing' Fe2+ ions, the crystal contains two Fe3+ ions to balance the charge .   i.e. 3Fe2+ = 2Fe3+ to maintain electrical neutrality