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'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 inter molecular forces between these molecules?

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Short Answer Type

112.

How will you distinguish between the following pairs of terms:
Hexagonal close-packing and cubic close-packing?

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113.

How will you distinguish between the following pairs of terms:
Crystal lattice and unit cell?

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114.

How will you distinguish between the following pairs of terms:
Tetrahedral void and octahedral void?

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115. How many lattice points are there in one unit cell of each of the following lattice?
(i) face centered cubic
(ii) face centered tetragonal
(iii) body centered.

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116.
Explain the basis of similarities and differences between metallic and ionic crystals.

The similarities and differences between metallic and ionic crystals are described as below:

Characteristics		Ionic crystals	Metallic crystals
1.	Constituent particles	cations (positive ions) and anions (negative ions)	Positive ions and mobile electrons.
2.	Binding forces	Strong electrostatic forces (electro valent bonding)	Electrical attraction between positive ions and mobile electrons (metallic bonding)
3.	Physical properties	Hard and brittle; high m.p. and b.p. good conductors of heat and electricity in molten state and aqueous solution, high heat of fusion.	Hard but malleable, high m.p., very good conductors of heat and electricity in solid and molten state, moderate heats of fusion.