Unit 1 The Solid State (Intext Questions-5)-Deleted
Intext Questions
1.18 What type of defect can arise when a solid is heated? Which physical property is affected by it and in what way?
Answer When a solid is heated, vacancy defect can arise. A solid crystal is said to have vacancy defect when some of the lattice sites are vacant. Vacancy defect leads to a decrease in the density of the solid.Show Answer
Answer (i) ZnS shows Frenkel defect. (ii) AgBr shows Frenkel defect as well as Schottky defect.Show Answer
Answer When a cation of higher valence is added to an ionic solid as an impurity to it, the cation of higher valence replaces more than one cation of lower valence so as to keep the crystal electrically neutral. As a result, some sites become vacant. For example, when $\mathrm{Sr}^{2+}$ is added to $\mathrm{NaCl}$, each $\mathrm{Sr}^{2+}$ ion replaces two $\mathrm{Na}^{+}$ions. However, one $\mathrm{Sr}^{2+}$ ion occupies the site of one $\mathrm{Na}^{+}$ion and the other site remains vacant. Hence, vacancies are introduced.Show Answer
Answer 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 $\mathrm{NaCl}$ 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 $\mathrm{NaCl}$ with the deposited $\mathrm{Na}$ atoms. During this process, the $\mathrm{Na}$ atoms on the surface lose electrons to form $\mathrm{Na}^{+}$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.Show Answer
Answer Ann-type semiconductor conducts because of the presence of extra electrons. Therefore, a group 14 element can be converted to $n$-type semiconductor by doping it with a group 15 element.Show Answer
Show Answer
Answer
Ferromagnetic substances would make better permanent magnets.
In solid state, the metal ions of ferromagnetic substances are grouped together into small regions. These regions are called domains and each domain acts as a tiny magnet. In an unmagnetised piece of a ferromagnetic substance, the domains are randomly oriented. As a result, the magnetic moments of the domains get cancelled. However, when the substance is placed in a magnetic field, all the domains get oriented in the direction of the magnetic field and a strong magnetic effect is produced.
The ordering of the domains persists even after the removal of the magnetic field. Thus, the ferromagnetic substance becomes a permanent magnet.
