ï»¿ 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? from Chemistry The Solid State Class 12 Nagaland Board

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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?

Co-ordination number : The total number of nearest neighbour atoms of a particular atom in a crystal lattice is known as its co-ordination number.

Example: In hexagonal close-packing (hcp) arrangement, each particle is surrounded by 12 equidistant spheres, i.e., 6 spheres in contact with in the same plane and 3 each in adjacent layers-one immediately above and the other immediately below. This, co-ordination number in hcp packing is 12.

(ii) The coordination number of atoms

(a) In a cubic close-packed structure is 12

(b) In a body-centered cubic structure is 8

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Classify the following as amorphous or crystalline solids: Polyurethane, naphthalene, benzoic acid, teflon, potassium nitrate, cellophane, polyvinyl chloride, fibre glass, copper.

Amorphous solids: Polyurethane, teflon, cellophane, polyvinyal chloride, fibre glass.
Crystalline solids: naphthlene, benzoic acid, potassium nitrate, copper.
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Refractive index of a solid is observed to have the same value along all directions. Comment on the nature of this solid. Would it show clevage property?

Refractive index of a solid which have the same value along all directions are isotropic in nature. It would not show cleavage property.
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Why do solids have a definite volume?

A solid have a definite volume because the inter molecular distance  between its molecules are fixed.
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Why is glass considred a super-cooled liquid?

Glass is amorphous solids and  have a tendency to flow, though very slowly. Therefore, these are called pseudo solids or super cooled liquids .
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Why are solids rigid?

Solids are rigid because the internuclear distance between the  molecules of a solid are very less and closely packed and their positions are fixed due to the strong forces of attraction between them.
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