In terms of band theory, what is the difference?

(i) Between a conductor and an insulator

Solution: In conductors there is no energy gap between the valance band, which facilitates the flow of electrons easily under an applied electric field and metals show conductivity. While in insulators there is no energy gap between the valance band and electrons cannot jump to it i.e. large energy gap prevents the flow of electricity.

(ii) Between a conductor and a semiconductor?

Solution: Difference between conducts and semiconductors – In conductors is no energy gap between the valance band and conduction band, electrons to jump to the conduction band by acquiring extra energy.

 

 

 

(i) Explain Schottky defect terms with suitable examples 

 

Solution: When cations and anions both are missing from regular sites, the defect is called Schottky Defect. In Schottky Defects, the number of missing cations is equal to the number of missing anions in order to maintain the electrical neutrality of the ionic compound. Scottky Defect is type of simple vacancy defect and shown by ionic solids having cations and anions; almost similar in size, such as NaCl, KCl, CsCl, etc. AgBr shows both types of defects, i.e. schottky and Frenkel Defects. Since, Schottky Defects arises because of mission of constituent particles, thus it decreases the density of ionic compound. 

 

 

 

Explain Frenkel defect terms with suitable examples

 

Solution: It is a type of vacancy defect. In ionic compounds, some of the ions (usually smaller in size) get dislocated from their original site and create defect. This defect is known as frenkel defect. Since this defect arises because of dislocation of ions, thus it is also known as dislocation defect. As there are a number of cations and anions (which remain equal even because of defect); the density of the substance does nnot increase or decrease. Ionic compounds; having large difference in the size between their cations and anions; show Frenkel Defect, such as ZnS, AgCl, AgBr, AgI, etc. these compounds have similar size of cations compared to anions. 

 

Explain Interstitials terms with suitable examples

 

Solution: Sometimes in the formation of lattice structure some of the atoms or ions occupy vacant interstitial site, and are known as interstitials. These interstitials are generally small size non- metals, such as H, B, C, etc. Defect arises because of interstitials is called the interstitial defect.

 

 

 

Explain F-centres terms with suitable examples

 

Solution: This is a type of defect and is also called as the metal access defect. These type of defects are seen because of missing of anions from regular site leaving a hole which is occupied by electron to maintain the neutrality of the compound. Hole occupied by electron is called F – centre and is responsible for showing colour by the compound.

 

 

 

25. If NaCl is doped with 10–3 mol % of SrCl2, what is the concentration of cation vacancies?

 

Solution: We know that two Na 2+ ions are replaced by each of the Sr2+ ions while SrCl2 is doped with NaCl. But in this case only one lattice point is occupied by each other of the Sr2+ ion and produce one cation vacancy. Here 10-3 mole of SrCl2 is doped with 100 moles of NaCl.

 

Thus, cation vacancies produced by NaCl = 10 -3mol

 

Therefore, 1 mole of NaCl will produce cation vacancies after doping

 

=10^(-3)/100 = 10-5 mol

 

Therefore, total cationic vacancies

 

 = 10-5 × Avogadro’s number

 

 = 10-5 × 6.022 × 10 23

 

 = 6.023 × 10 -18 vacancies.

 

 

 

 

 

 

 

 

 

Explain what is Ferromagnetism with suitable examples? 

 

Solution: (i) Ferromagnetism

 

Substances that are attracted strongly with magnetic field are called ferromagnetic substances, such as Cobalt, Nickel, Iron, gadolium, chromium oxide, etc. ferromagnetic substances are permanently magnetized. Metal ions of ferromagnetic substances are randomly oriented in normal condition and substances do not act as a magnet. But when metal ions are grouped together in small regions, called domains, each domain acts as a tiny magnet and produces strong magnetic field, in such condition ferromagnetic substances becomes a permanent magnet.

 

 

 

Explain what is Paramagnetism with suitable examples? 

 

 

 

 

 

Solution: The substances which are attracted slightly by magnetic field and fo not retain the magnetic property after removal of magnetic field are called paramagnetic substances. For example, o2, Cu2+,Fe3+,Cr3+, magnesium, lithium, etc. substance show paramagnetism because of the presence of unpaired electrons. These unpaired electrons are attracted by magnetic field.  

 

Explain what is Ferrimagnetism with suitable examples? 

 

Solution: Substances which are slightly attracted in magnetic field and in which domains are grouped in parallel and anti – parallel direction but in unequal number, are called ferromagnetic substances and this property is called as ferromagnetism.

 

For example, magnetite (Fe3O4), ferrite (MgFe2O4), ZnFe2O4, etc.

 

Explain what is Antiferromagnetism with suitable examples? 

 

Substances in which domain structure are similar to ferromagnetic substances but are oriented to oppositely, which cancel the magnetic property are called antiferromagnetic substances and this property is called antiferromagnetism. For example, MnO.

 

Explain what is 12-16 and 13-15 group compounds with suitable examples? 

 

 

 

Compounds belong to 12 – 16 group are formed by combination of elements of 12 and 16 groups. For example – ZnS, Cds, etc.

 

Compounds belong to 13 – 15 groups are formed by the combination of the elements of 13 and 15groups, for example, InSb, GaAs, etc.

 

Bonds in these compounds are not perfectly covalent. The ionic bonds in these compounds depend s on the electronegativity of the two elements.