1. What is a crystal? (or) What are crystalline materials? Give examples.
Crystalline solids (or) crystals are those, in which the constituent atoms (or) molecules are arranged in an orderly fashion throughout in a three dimensional pattern.
Example : Copper, Silver.
2. What is an amorphous solid? Give example.
It is a type of solid, in which the atoms (or) molecules are not arranged in an orderly fashion. i.e., The same atomic groups are arranged more randomly.
Example : Plastics, rubber.
3. What is a primitive cell?
A primitive cell is the simplest type of unit cell, which contains one lattice point per unit cell.
4. Define unit cell.
The unit cell is defined as the smallest geometric figure, the repetition of which gives the actual crystal structure. It is also defined as the fundamental elementary pattern or building block of minimum atoms, molecules (or) group of molecules which represents all the characteristics of the crystal.
5. What are the differences between crystalline and noncrystalline materials.
| S.No | Crystalline solids | Amorphous solids |
| 1. | Regular arrangement of atom gives definite and geometric shape. | Random arrangement of atom does not give definite and geometrical shape. |
| 2. | They are anisotropic. | They are isotropic. |
| 3. | They have sharp melting point. | They do not have sharp melting point. |
| 4. | Examples: Diamonds, NaCl , KCl, Copper , etc. | Examples: Glass , Plastic, Rubber, etc. |
6. Define space lattice (or) crystal lattice.
A space lattice is defined as regular and periodic arrangement of atoms (or points) in three dimensional space.
Any atom has got the same surroundings as any other atoms.
7. What is a basis?
A unit assembly of atoms (or) molecules (i.e., one or more atoms (or) molecules) identical in composition, arrangement and orientation is called the Basis.
8. What is a crystal structure?
A crystal structure is formed by associating a basis to every lattice point in a space lattice.
i.e., crystal structure = basis + space lattice.
10. What are Bravais lattices?
11. Name the crystal structure of the following.
- Gold
- Germanium
- Barium
- Zinc
Ans:
- Gold – FCC
- Germanium – Diamond cubic
- Barium- BCC
- Zinc – HCP
All the above elements exhibit the structures given above at 20°C. But for Barium other structures also exists at other temperatures.
12. Bismuth has a=b=c=4.74AU and angles α=β=γ=60°. What is its crystal structure?
Solution : Given a=b=c=4.74AU, α=β=δ=60°
Since a=b=c and α=β=γ crystal structure of Bismuth is Trigonal (or) Rhombohedral.
13. Define coordination number.
It is the number of nearest neighbouring atoms to any particular atom in the lattice array (or) Coordination number is the number of nearest neighbours directly surrounding a given atom.
14. Define atomic radius.
It is defined as half the distance between two nearest neighbouring atom in a crystal of a pure element.
15. Define atomic packing factor (or) packing density (or) density of packing.
It is defined as the ratio of the volume of atoms per unit cell to the total volume of the unit cell.
A P F=\frac{\text { No. of atoms present in a unit cell } \times \text { Volume of one atom }}{\text { Volume of the unit cell }}16.Give the relation between the density of the crystal and the lattice constant.
The relation is ρ=nA /Na3
Where n is the number of atoms per unit cell, N is the Avagadro number, A is the atomic weight and a is the lattice constant.
17. Define inter-atomic distance and inter planar distance.
Inter-atomic distance: The distance between the centres of any two nearest atoms is called inter-atomic distance.
Inter planar distance: The distance between any two parallel planes is called inter-planar distance.
18. What are the miller indices?
Miller indices are the smallest possible integers which have the same ratios as the reciprocals of the intercepts of the plane concerned on the three axes.
19. What is crystal growth?
“Crystal growth is the process of converting a random oriented or a polycrystalline material into an orderly arranged crystalline material.”
20. What is solution growth method?
In the solution growth method, a super-saturated solution of the given substance is prepared, and it is kept without any disturbance at a constant low temperature. Single crystals begin to grow from supersaturated solution after some days or week or month. Then the entire supersaturated solution gets converted into a large size single crystals.
21. What is melt growth method?
Melt growth is the process of crystallization by fusion and resolidification of the pure material by cooling the liquid below its freezing point.
22. What are the necessary steps involved in the crystallization process?
- achievement of supersaturation or supercooling.
- formation of crystal nuclei.
- successive growth of crystals to get distinct faces.
| Read More Topics |
| Properties of matter – Questions and Answers |
| Dielectric materials – Questions and Answers |
| Crystal physics – Solved Problems |
