Ionic
solids, which have anionic vacancies due to metal excess defect,
develop colour. Explain with the help of a suitable example.
Ionic solids, which have anionic vacancies due to metal excess defect, develop colour. Explain with the help of a suitable example.
The
colour develops because of the presence of
electrons in the anionic sites. These electrons absorb energy from
the visible part of radiation and get excited.
For
example, when crystals of NaCl are heated in an atmosphere of sodium
vapours, the sodium atoms get deposited on the surface of the crystal
and the chloride ions from the crystal diffuse to the surface to form
NaCl with the deposited Na atoms. During this process, the Na atoms
on the surface lose electrons to form Na+
ions and the released electrons diffuse into the crystal to occupy
the vacant anionic sites. These electrons get excited by absorbing
energy from the visible light and impart yellow colour to the
crystals.
The colour develops because of the presence of electrons in the anionic sites. These electrons absorb energy from the visible part of radiation and get excited.
For example, when crystals of NaCl are heated in an atmosphere of sodium vapours, the sodium atoms get deposited on the surface of the crystal and the chloride ions from the crystal diffuse to the surface to form NaCl with the deposited Na atoms. During this process, the Na atoms on the surface lose electrons to form Na+ ions and the released electrons diffuse into the crystal to occupy the vacant anionic sites. These electrons get excited by absorbing energy from the visible light and impart yellow colour to the crystals.
