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(a) Based on the nature of the intermole...

(a) Based on the nature of the intermolecular foces, classify solids benzene and silver.
(b) AgCl shows frenkel defect while NaCl does not. Give reason.
(c) What type of semi-conductor is formed when Ge is doped with Al ?

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(a) Benzene: Molecular (non-polar)-solid, silver: Metallic-solid
(b) Frenkel defect is shown by those in which there is large difference in the size of cations and anions. Hence, frenkel defect is shown by AgCl due to small size of `Ag^(+)` ion but not by NaCl because alkali metal ions can not fit into interstitial sites.
(c) P-type semiconductor is formed when Ge(gp-14) is dopped with Al(gp-13). One electron hole is created.
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When an atom or an ion is missing from its normal lattice site, a lattice vacancy (Schottky detect) is created In stoichiometric ionic crystals, a vacancy of one ion has to be accompanied by the vacancy of the oppositely charged ion in order to maintain electrical neutrality. In a Frenkel defect an ion leaves its position in the lattice and occupies an interstitial void.This is the Frenkel defect commonly found along with the Schottky defects and interstitials.In pure alkali halides, Frendel defect are not found since the ions cannot get into the intenstitial sites.Frenkel defects are found in silver halides because of the small size of the Ag^+ ion.Unlike Schottky defects. Frenkel defects do not change the density of the solids.In certain ionic solids (e.g. AgBr) both Schottky and Frenkel defects occur. The defects discussed above do not disturb the stoichiometry of the crystalline meterial.There is large Such solids showing deviations from the ideal stoichiometric composition form an important group of solids For example in the vanadium oxide, VO_x , x can be anywhere between 0.6 and 1.3.There are solids which are difficult to prepare in the stoichiometric composition.Thus, the ideal composition in compounds such as FeO is difficult to obtain (normally we get a composition of Fe_(0.85) O but it may range from Fe_(0.93) O to Fe_(0.96)O ).Non-stoichiometric behaviour is most commonly found for transition metal compounds through is also known for some lanthanoids and actinodes. Zinc oxide loses oxygen reversibly at high temperature and turns yellow in colour.The excess metal is accomdated interstitially, giving rise to electrons trapped in the neighbourhood.the enhanced electrical conductivity of the non-stoichiometric ZnO arises from these electrons . Anion vacancies in alkali halides are produced by heating the alkali halide crystals in an atmosphere of the alkali metal vapour.When the metal atoms deposite on the surface they diffuse into the crystal and after ionisation the alkali metal ion occupies cationic vacancy whereas electron occupies anionic vacancy.Electrons trapped in anion vacancies are referred to as F-centres (from Farbe the German word for colour) that gives rise to interesting colour in alkali halides.Thus, the excess of potassium in KCl makes the crystal appear violet and the excess of lithium in LiCl makes it pink. In the crystal of Fe_(0.93)O , the percentage of Fe (II) will be

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