Unit 1 The Solid State (Intext Questions-3)-Deleted
Intext Questions
1.9 Give the significance of a ‘lattice point’.
Answer The significance of a lattice point is that each lattice point represents one constituent particle of a solid which may be an atom, a molecule (group of atom), or an ion.Show Answer
Answer The six parameters that characterise a unit cell are as follows. (i) Its dimensions along the three edges, $a, b$, and $c$ These edges may or may not be equal. (ii) Angles between the edges These are the angle $\propto$ (between edges b and c), (between edges a and c), and (between edges a and b)Show Answer
(i) Hexagonal and monoclinic unit cells
(ii) Face-centred and end-centred unit cells.
Answer (i) Hexagonal unit cell For a hexagonal unit cell, $a=b \neq c$ and $\alpha=\beta=90^{\circ}$ $\gamma=120^{\circ}$ Monoclinic unit cell For a monoclinic cell, $a \neq b \neq c$ and $\alpha=\gamma=90^{\circ}$ $\beta \neq 90^{\circ}$ (ii) Face-centred unit cell In a face-centred unit cell, the constituent particles are present at the corners and one at the centre of each face. End-centred unit cell Anend-centred unit cell contains particles at the corners and one at the centre of any two opposite faces.Show Answer
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Answer
(i) An atom located at the corner of a cubic unit cell is shared by eight adjacent unit cells.
Therefore, $\frac{1}{8}$ th portion of the atom is shared by one unit cell.
(ii) An atom located at the body centre of a cubic unit cell is not shared by its neighbouring unit cell. Therefore, the atom belongs only to the unit cell in which it is present i.e., its contribution to the unit cell is 1.
