﻿ How many lattice points are there in one unit cell of each of the following lattice?(a) face centred cubic(b) face centred tetragonal(c) body centred cubic from Chemistry The Solid State Class 12 Nagaland Board

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How many lattice points are there in one unit cell of each of the following lattice?
(a) face centred cubic
(b) face centred tetragonal
(c) body centred cubic

A face-centred cubic (fcc) unit cell contains atoms at all the corners and at the centre of all the faces of the cube.each atom located at the face-centre is shared between two adjacent unit cells and only 1/2 of each atom belongs to a unit cell

Thus, in a face-centred cubic
(fcc) unit cell:
(i) 8 corners atoms × 1/8 atom per unit cell = 8×1/8 = 1 atom
(ii) 6 face-centred atoms ×1/2 atom per unit cell = 6 ×1/2 = 3 atoms
∴ Total number of atoms per unit cell = 4 atoms

(a) z = 4,
(b) z = 4,

body centre wholly belongs to the unit cell in which it is present. Thus
in a body-centered cubic (bcc) unit cell:
(i) 8 corners × 1/8 per corner atom= 8×1/8 = 1 atom
(ii) 1 body centre atom = 1 × 1 = 1 atom
∴ Total number of atoms per unit cell =1+1 = 2

(c) z = 2.

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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.

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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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