Q. 223.8( 22 Votes )
Ionic solids, which have anionic vacancies due to metal excess defect, develop colour. Explain with the help of a suitable example.
To explain this, let us take an example of NaCl. When NaCl crystal is heated in presence of Na vapour, some Cl- ions leave their lattice sites to combine with Na to form Na+ (Na+ + Cl-⇒ NaCl) then diffuse into the crystal to occupy the anion vacancies. These sites are called as the F- centres. These electrons absorb energy from the visible light, get excited to higher energy level and when they fall back to the ground state they impart yellow colour to the NaCl crystal.
Rate this question :
Explain why does conductivity of germanium crystals increases on doping with gallium.Chemistry - Exemplar
Match the type of unit cell given in Column I with the features given in Column II.
An element crystallizes in a f.c.c. lattice with cell edge of 250 pm. Calculate the density if 300 g of this element contain atoms.Chemistry - Board Papers
The percentage of empty space in a body centred cubic arrangement is ________.Chemistry - Exemplar
In which pair most efficient packing is present?Chemistry - Exemplar
What type of stoichiometric defect is shown by?
(i) ZnS (ii) AgBrNCERT - Chemistry Part-I
Iodine molecules are held in the crystals lattice by ____________.Chemistry - Exemplar
How many lattice points are there in one unit cell of each of the following lattice?
Body-centredNCERT - Chemistry Part-I