Q. Niobium crystallises in body-centred cubic structure. If density is $8.55gc{m}^{-3}$, calculate atomic radius of niobium using its atomic mass $93U$.

Q. What is a semiconductor? Describe the two main types of semiconductors and contrast their conduction mechanism

Q. Copper crystallises into a fcc lattice with edge length $3.61\times {10}^{-8}cm$. Show that the calculated density is in agreement with its measured value of $8.92gc{m}^3$.

Q. (i) What is meant by the term 'coordination number'?
(ii) What is the coordination number of atoms:
(a) in a cubic close-packed structure?
(b) in a body-centred cubic structure?

Q. Ferric oxide crystallises in a hexagonal close-packed array of oxide ions with two out of every three octahedral holes occupied by ferric ions. Derive the formula of the ferric oxide.

Q. What makes a glass different from a solid such as quartz? Under what conditions could quartz be converted into glass?

Q. Silver crystallises in fcc lattice. If edge length of the cell is $4.07\times {10}^{-8}cm$ and density is $10.5gc{m}^{-3}$, calculate the atomic mass of silver.

Q. Analysis shows that nickel oxide has the formula $N{i}_{0.98}{O}_{1.00}$. What fractions of nickel exist as $N{i}^{2+}$ and $N{i}^{3+}$ ions?

Q. If the radius of the octahedral void is $r$ and radius of the atoms in close-packing is $R$, derive relation between $r$ and $R$.

Q. Non-stoichiometric cuprous oxide, $C{u}_{2}O$ can be prepared in laboratory. In this oxide, copper to oxygen ratio is slightly less than $2:1$. Can you account for the fact that this substance is a p-type semiconductor?

Q. Calculate the efficiency of packing in case of a metal crystal for the following crystal structure (with the assumptions that atoms are touching each other):

Q. Stability of a crystal is reflected in the magnitude of its melting points. Comment. Collect melting points of solid water, ethyl alcohol, diethyl ether and methane from a data book. What can you say about the intermolecular forces between these molecules?

Q. How can you determine the atomic mass of an unknown metal if you know its density and the dimension of its unit cell? Explain.

Q. A cubic solid is made of two elements P and Q. Atoms of Q are at the corners of the cube and P at the body-centre. What is the formula of the compound? What are the coordination numbers of P and Q?

Q. Define the term 'amorphous'. Give a few examples of amorphous solids.

Q. Explain
(i) The basis of similarities and differences between metallic and ionic crystals.
(ii) Ionic solids are hard and brittle.

Q. How will you distinguish between the following pairs of terms:
(i) Hexagonal close-packing and cubic close-packing?
(ii) Crystal lattice and unit cell?
(iii) Tetrahedral void and octahedral void?

Q. How many lattice points are there in one unit cell of each of the following lattice?
(i) Face-centred cubic
(ii) Face-centred tetragonal
(iii) Body-centred

Q. Classify each of the following solids as ionic, metallic, molecular, network (covalent) or amorphous.
(i) Tetra phosphorus decoxide $\left(P_4{O}_{10}\right)$ (ii) Ammonium phosphate $(N{H}_4{)}_{3}P{O}_4$ (iii) SiC (iv) $I_2$ (v) $P_4$ (vi) Plastic (vii) Graphite (viii) Brass (ix) Rb (x) LiBr (xi) Si

Q. Classify each of the following as being either a p-type or a n-type semiconductor:
(i) Ge doped with In (ii) Si doped with B