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The anionic sites occupied by unpaired e...

The anionic sites occupied by unpaired electrons are called F-centres or colour centres . They impart __(X)__ colour to the crystals of NaCl. Excess of lithium makes LiCl crystals __(Y)__and excess of potassium makes KCl crystals _(Z)___. (X),(Y) and (Z) are

A

yellow, green and pink respectively

B

pink , yellow and violet (or lilac) respectively

C

yellow, pink and violet (or lilac ) respectively

D

red, yellow and pink respectively

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To solve the question, we need to identify the colors associated with the F-centres in NaCl, LiCl, and KCl crystals when there is an excess of sodium, lithium, and potassium, respectively. ### Step-by-Step Solution: 1. **Understanding F-centres**: - F-centres are anionic sites in a crystal lattice that are occupied by unpaired electrons. These defects occur due to the presence of anionic vacancies in the crystal structure. 2. **Color Imparted by F-centres in NaCl**: - When NaCl crystals are heated in the presence of sodium vapour, sodium atoms are deposited on the surface, and chlorine ions migrate to the surface, leaving behind vacancies. The unpaired electrons occupy these vacancies, leading to the formation of F-centres. - These F-centres in NaCl impart a **yellow color** to the crystals. - Therefore, we conclude that **(X) = yellow**. 3. **Effect of Excess Lithium on LiCl Crystals**: - When there is an excess of lithium in LiCl, the presence of F-centres results in the crystals exhibiting a **pink color**. - Thus, we find that **(Y) = pink**. 4. **Effect of Excess Potassium on KCl Crystals**: - Similarly, when there is an excess of potassium in KCl, the F-centres lead to the crystals displaying a **violet (or lilac) color**. - Therefore, we determine that **(Z) = violet**. 5. **Final Answers**: - Putting it all together, we have: - (X) = yellow - (Y) = pink - (Z) = violet Thus, the final answer is: (X) = yellow, (Y) = pink, (Z) = violet.
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An excess of potassium ions makes KCL crystals appear violet or lilac in colour since …………. .

An excess of potassium ions makes KCL crystals appear violet or lilac in colour since …………. .

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When an atom or an ion is missing from its normal lattice site, a lattice vacancy (Schottky defect) is created. In stoichimetric 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, Frenkel defects are not found since the ions cannot get into the interstitial 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 denstiy of the solids. In certain ionic solids (e.q. AgBr) both Schottky and Frenkel defects occur. The defects discussed above do not disturb the stoichiometry of the crystalline material. There is large variety of non-stoichiomertic inorganic solids which contain an excess or deficiency of one of the elements. Such solids showing deviations from the ideal stoichiometric composition from an inmportant 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_(0.95)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 though is also known for some lanthanoids and actinoids. Zinc oxide loses oxygen reversibly at high temperature and turns yellow in colour. The excess metal is accommodated interstitially, giving rise to electrons trapped in the neighbourhood. The enhanced electrical conductivity of the non-stoichiometric ZnO arises from these electrons.ltrbgt Anion vacancies in alkali halides are produced by heating the alkali halide crystals in an atmosphere of the alkali metal vapur. When the metal atoms deposit 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-centers (from Farbe the German word for colour) that given rise to interesting colour in alkali halides. Thus, the excess of potassium in KCl makes the crytal appear violet and the excess of lithium in LiCl makes it pink. When LiCl is heated into the vapour of lithium, the crystal acquires pink colour. This is due to

When an atom or an ion is missing from its normal lattice site, a lattice vacancy (Schottky defect) is created. In stoichimetric 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, Frenkel defects are not found since the ions cannot get into the interstitial 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 denstiy of the solids. In certain ionic solids (e.q. AgBr) both Schottky and Frenkel defects occur. The defects discussed above do not disturb the stoichiometry of the crystalline material. There is large variety of non-stoichiomertic inorganic solids which contain an excess or deficiency of one of the elements. Such solids showing deviations from the ideal stoichiometric composition from an inmportant 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_(0.95)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 though is also known for some lanthanoids and actinoids. Zinc oxide loses oxygen reversibly at high temperature and turns yellow in colour. The excess metal is accommodated interstitially, giving rise to electrons trapped in the neighbourhood. The enhanced electrical conductivity of the non-stoichiometric ZnO arises from these electrons.ltrbgt Anion vacancies in alkali halides are produced by heating the alkali halide crystals in an atmosphere of the alkali metal vapur. When the metal atoms deposit 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-centers (from Farbe the German word for colour) that given rise to interesting colour in alkali halides. Thus, the excess of potassium in KCl makes the crytal appear violet and the excess of lithium in LiCl makes it pink. Stongly heated ZnO crystal can conduct electricity. This is due to

When an atom or an ion is missing from its nomal lattice site a lattice vacanecy (Schottky defect) is created. In stoichmeteric ionic crystals, a vacancy of one ion has to be accompanied by the vacancy of the oppositely charge 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 id the Frenkel defect commonly found along with the Schottky defects and interstitial. In pure alkali halides. Frenked defects are not found since the ions cannot get into the interstitial sites. Frenkel defects are found in silver halides because of the small size of the Ag^(+) ion. Unike Schottky defects, Frenkel defect do not change the density of the solids. in certain ionic solids (e.g., AgBr) both schottky and Frenkel defect occur. The Defects idiscussed above do not disturb the stoichiometery of the crystalline material. there is large variety of non-stoichiometric inorganic solids which contains an excess or deficienty of one of the elements. Such solids showing deviations from the ideal stoichiometric composition from an important group of solids. For example in the vanadium oxide, VO_(x),x can be anywehere between 0.6 and 1.3 there are solids such as difficult to prepare in the soichiometric omposition thus, the ideal composition in compounds such as FeO is difficult to obtain (normally we get a compositiion of Fe(0.95) O but it may range from Fe_(0.93) O to Fe_(0.96)O ). Non-stoichiometric behavious is most commonly found for transition metal compounds through is also known for some lathanoids and actinoids. Zinc oxide loses oxygen reversible at high temperature and turns yellow in colour. the excess metal is accomodated interstitial, giving rise to electrons trapped in the neighbourhood, the enchanced electrical conductivity of the non-stoichiometric ZnO arises from these electrons. Anion vacancies in alkali halides are produced by heating the alkali halid crystals in an atmosphere of the alkali metal vapour. when the metal atoms deposit on the surface they diffuse into the cystal and after ionisation the alkali metal ion occupies cationic vacancy whereas electron occupies anionic vacancy. Electrons trapped i anion vacancies are referred to as F-centers (From Farbe the German word for colouf) that gives rise to interesting colour in alkali halides. Thus, the excess of potassium i KCl makes the crystal appear violet and the excess of lithium in LiCl makes it pink. Which of the following is most appropritate crystal to show Fremkel defect ?

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