Class 12 chemistry chapter 1 includes the topic – General characteristics of solid state. Amorphous and crystalline solids. Difference between amorphous and. NCERT Solutions For Class 12 Chemistry Chapter 1 The Solid State. NCERT TEXTBOOK QUESTIONS SOLVED. Why are solids rigid? NCERT Class XII Chemistry: Chapter 1 – The Solid State. National Council of Educational Research and Training (NCERT) Book for Class XII Subject.


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The unit cell of silver iodide AgI has 4 iodine atoms in it. How many silver atoms must be there in the unit cell. What must be the co-ordination number of the fluoride ions. Imperfections in a Crystal The discovery of imperfections in an other wise ideally perfect crystal is one of the most fascinating aspects of solid state science.

An ideally perfect crystal is one which solid state chemistry 12th the same unit cell and contains the same solid state chemistry 12th points throughout the crystal.

The term imperfection or defect is generally used to describe any deviation of the ideally perfect crystal from the periodic arrangement of its constituents.


Point Defect If the deviation occurs because of solid state chemistry 12th atoms, displaced atoms or extra atoms, the imperfection is named as solid state chemistry 12th point defect.

Such defects can be the result of imperfect packing during the original crystallisation or they may arise from thermal vibrations of atoms at elevated temperatures because with increase in thermal energy there is increased probability of individual atoms jumping out of their positions of lowest energy.


The most common point defects are the Schottky defect and the Frenkel defect. Comparatively less common point defects are the metal excess defect and the metal deficiency defects.


All these defects have been discussed below in some details. The defects arise if some of the lattice points in a solid state chemistry 12th are unoccupied.

The points which are unoccupied are called lattice vacancies. The crystal, as a whole remains neutral because the number of missing positive and negative ions is the same.

Figure 16 Schottky defects appear generally in ionic crystals in which the positive solid state chemistry 12th the negative ions do not differ much in size.

Sodium chloride and cesium chloride furnish good examples of ionic crystals in which Schottky defects occurs.

Class 12 Chemistry Revision Notes for Chapter 1 - The Solid State

These defects arise when an ion occupies an interstitial position between the solid state chemistry 12th points. This is shown in figure for the crystal of AgBr. A vacancy is thus created in the lattice as shown.

It may be noted again that the crystal remains neutral since the number of positive ions is the same as the number of negative ions.

ZnS is another crystal in which Frenkel defects appear.

NCERT Solutions Class 12 Chemistry Chapter 1 Solid State - Download Now

Frenkel defects appear in crystals in which the negative ions are much larger than solid state chemistry 12th positive ions.

Like Schottky defects, the Frenkel defects are also responsible for the conduction of electricity in crystals and also for the phenomenon of diffusion in solids.

It has been observed that if a crystal of NaCl is heated in sodium solid state chemistry 12th, it acquires a yellow colour. This yellow colour is due to the formation of a non-stoichiometric compound of sodium chloride in which there is a slight excess of sodium ions.

This electron occupies a site that would otherwise be filled by a chloride ion, as illustrated in figure. Figure 18 There is evidently an excess of metal ions although the crystal as a whole is neutral. On the other hand, this electron is similar to the delocalised p electrons present in molecules containing conjugate double bonds.

Light is absorbed when this delocalised electron makes an easy solid state chemistry 12th from its ground state to an solid state chemistry 12th state.

NCERT Class XII Chemistry: Chapter 1 – The Solid State

As a result, the non stoichiometric form of sodium chloride appears coloured. Because of this, the sites occupied by solid state chemistry 12th extra electrons are known as colour centres.

These are also called F-centres. This name comes from the German word Farbe meaning colour.

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