CBSE Class 12-science Answered

1. Mention the characteristic properties of solid. 2. Mention the differences between crystalline solid and amorphous solid. 3. Explain the terms a) anisotropy b) isotropy. Why is crystalline solid anisotropic while amorphous solid isotropic in nature? 4. What makes glass different from quartz? Under what condition quartz is converted to glass? 5. Why are amorphous solids called pseudo solids or super cooled liquids? 6. How are crystalline solids classified on the basis of intermolecular forces? Give two examples of each type and mention their properties. 7. Compare the properties of diamond and graphite on the basis of their structures. 8. Classify the following as ionic, metallic, molecular, covalent, or amorphous. a) P4O10 b) (NH4)3PO4 c) I2 d) Plastic e) graphite f) Brass g) Rb h) LiBr i) Si 9. How are molecular solids subdivided further? Give two examples each and mention their properties. 10. Account for the following: a) Glass panes fixed to windows of old buildings becomes slightly thicker at the bottom than at the top. b) NaCl(s) does not conduct electricity but it conducts either in molten state or in aqueous solution. c) Diamond is a non conductor while graphite is a conductor of electricity. d) Diamond is hard while graphite is soft. e) Graphite is a lubricant. f) Ionic solids are hard and brittle. g) MgO and NaCl are ionic solids but MgO has higher melting point than NaCl. h) NaCl exhibit schottky defect and not frenkel defect. 11. Explain the terms a) lattice point b) crystal lattice c) unit cell. 12. What are Bravis lattices? Mention the characteristics of a crystal lattice. 13. Mention the characteristics of a unit cell. Draw a neat diagram of a unit cell and show its parameters.

Asked by Shubham Goyal | 09 Mar, 2013, 07:01: AM

Expert Answer

The general characteristics of solids are as follows. As mentioned above, solids have two main properties.

They have strong intermolecular forces and short internuclear distance due to close packing of constituent particles.
Their constituent particles don’t possess translator motion but can oscillate only around their mean position.

Due to these two basic properties, solids possess the following characteristic properties.

They have definite shape, mass and volume.
They are rigid and incompressible.
They have high density.

Comparison between Crystalline Solids and Amorphous Solids

Crystalline solids	Amorphous solids
Crystals have definite and regular geometry and have long range as well as short range order of constituent particles.	The particles in the constituent are arranged irregularly. They do not have any definite geometry and have short range order.
Crystals posses high melting points.	They are devoid of sharp melting points.
The crystals external forms have regularity when these are formed.	No external regularity in their form when these amorphous solids are formed.
They give a clean surface after cleavage with knife.	Usually the amorphous solids exhibit irregular cut.
They have definite heat of fusion.	Amorphous solids do not possess any particular heat of fusion.
Crystalline solids are very rigid and their molecules cannot be deformed by mild distorting force.	Amorphous solid do not exhibit rigidity. Deformation could be done by bending or compressing them.
Crystalline solids are considered as true solid.	Amorphous solids are considered as super cooled liquids or also pseudo solids.
Crystalline solids display anisotropism.	Amorphous solids display isotropism.