The Solid State

The Solid State

Question

(i) What type of non-stoichiometric point defect is responsible for the pink colour of LiCl?
(ii) What type of stoichiometric defect is shown by NaCl?

OR
How will you distinguish between the following pairs of terms:
(i) Tetrahedral and octahedral voids
(ii) Crystal lattice and unit cell.

Answer

i) The pink colour of LiCl is because of the metal excess defect caused by the anionic vacancies.
ii) NaCl shows Schottky defect. In the Schottky defect, an equal number of cations and anion are missing from their regular sites.

Or
(i) Tetrahedral void surrounded by four spheres is called a tetrahedral void.

Octahedral void surrounded by six spheres is called an octahedral void.

(ii) Crystal lattice: A crystal lattice is a diagrammatic representation of the constituent particles such as atoms, ions and molecules of a crystal in a regular three-dimensional arrangement.
Unit cell: A unit cell is the smallest three-dimensional portion of a crystal lattice. When it is repeated in different directions, it generates the entire crystal lattice.

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