Solid State MCQ Questions & Answers in Physical Chemistry | Chemistry

In orthorhombic crystal system, $$a \ne b \ne c$$   but axial angles $$\alpha ,\beta $$  and $$\gamma $$  are equal and $${90^ \circ }.$$

Packing efficiency of $$ccp$$  or $$fcc$$  = 74%
Packing efficiency of $$bcc$$  = 68%
Packing efficiency of simple cubic = 52.4%
Thus, the correct order of the packing efficiency is $$fcc > bcc > {\text{simple cubic}}$$

4 formula units of $$AB$$  are present in a unit cell
∴ no. of unit cell $${\text{ = }}\frac{4}{{40}} \times \frac{{{N_A}}}{4}$$
$$ \Rightarrow 0.025\,{N_A}$$

Among the given crystals only silicon is as a covalent solid.

$$\eqalign{ & {\text{Unit cell length for}}\,\,fcc = 3.5\mathop {\text{A}}\limits^{\text{o}} \cr & {\text{Unit cell length for}}\,\,bcc = 3.0\mathop {\text{A}}\limits^{\text{o}} \cr & \therefore \,{\text{Density in}}\,\,fcc = \frac{{{Z_{fcc}} \times M}}{{{V_1} \times {N_A}}} \cr & \,\,\,\,\,\,{\text{Density in}}\,\,bcc = \frac{{{Z_{bcc}} \times M}}{{{V_2} \times {N_A}}} \cr & {\text{or}}\,\,\frac{{{\text{Density}}\left( {fcc} \right)}}{{{\text{Density}}\left( {bcc} \right)}} \cr & = \frac{{{Z_{fcc}}}}{{{Z_{bcc}}}} \times \frac{{{V_2}}}{{{V_1}}} \cr} $$
$$=\frac{4}{2}\times \frac{V_2}{V_1}\left[\begin{array}{l}\therefore \text{for}fcc,Z_{fcc}=4\\ \therefore \text{for}bcc,Z_{bcc}=2\end{array}\right]$$
$$\eqalign{ & {\text{Volume for}}\,\,fcc \cr & = {V_1} = {a^3} = {\left( {3.5 \times {{10}^{ - 8}}} \right)^3}c{m^3} \cr & {\text{and volume for}}\,\,bcc \cr & = {V_2} = {a^3} = {\left( {3.0 \times {{10}^{ - 8}}} \right)^3}c{m^3} \cr & \therefore \frac{{{\text{Density}}\left( {fcc} \right)}}{{{\text{Density}}\left( {bcc} \right)}} = \frac{{4 \times {{\left( {3.0 \times {{10}^{ - 8}}} \right)}^3}}}{{2 \times {{\left( {3.5 \times {{10}^{ - 8}}} \right)}^3}}} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 1.259\,\,{\text{or}}\,\,1.259:1 \cr} $$

Relation between radius of cation, anion and edge length of the cube
$$2{r_{Cs + }} + 2{r_{C{l^ - }}} = \sqrt 3 a \Rightarrow {r_{C{s^ + }}} + {r_{C{l^ - }}} = \frac{{\sqrt 3 a}}{2}$$

Since $$MgO$$  has a rock salt structure. In this structure each cation is surrounded by six anions and vice versa.

$${H_2}$$  and $${I_2}$$  are molecular solids.

The face centered cubic unit cell contains 4 atom
∴ Total volume of atoms
$$\eqalign{ & = 4 \times \frac{4}{3}\pi {r^3} \cr & = \frac{{16}}{3}\pi {r^3} \cr} $$

Conductors : $${10^4}\,\,{\text{to}}\,\,{10^7}oh{m^{ - 1}}{m^{ - 1}}$$
Insulators : $${10^{ - 20}}\,\,{\text{to}}\,\,{10^{ - 10}}oh{m^{ - 1}}{m^{ - 1}}$$
Semiconductors : $${10^{ - 6}}\,\,{\text{to}}\,\,{10^4}oh{m^{ - 1}}{m^{ - 1}}$$