Chemistry Class 12 NCERT Solutions: Chapter 1 the Solid State Part 12 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Q: 25. If is doped with what is the concentration of cation vacancies?


It is given that is doped with .

This means that 100 mol of is doped with

is doped with

Cation Vacancies produced by one

Concentration of the cation vacancies

Produced by

Hence, the concentration of cation vacancies created by is

Q: 26. Explain the following with suitable examples:

(i) Ferromagnetism

(ii) Paramagnetism

(iii) Ferrimagnetism

(iv) Antiferromagnetism

(v) group compounds


(i) Ferromagnetism:

The substances that are strongly attracted by a magnetic field are called ferromagnetic substances. Ferromagnetic substances can be permanently magnetised even in the absence of a magnetic field. Some examples of ferromagnetic substances are iron, cobalt, nickel, gadolinium, and .

In solid state, the metal ions of ferromagnetic substances are grouped together into small regions called domains and each domain acts as a tiny magnet. In an un-magnetised piece of a ferromagnetic substance, the domains are randomly oriented and so, their magnetic moments get cancelled. However, when the substance is placed in a magnetic field, all the domains get oriented in the direction of the magnetic field. As a result, a strong magnetic effect is produced. This ordering of domains persists even after the removal of the magnetic field. Thus, the ferromagnetic substance becomes a permanent magnet.


Schematic alignment of magnetic moments in ferromagnetic substances

(ii) Paramagnetism:

The substances that are attracted by a magnetic field are called paramagnetic substances. Some examples of paramagnetic substances are Paramagnetic substances get magnetised in a magnetic field in the same direction, but lose magnetism when the magnetic field is removed. To undergo paramagnetism, a substance must have one or more unpaired electrons. This is because the unpaired electrons are attracted by a magnetic field, thereby causing paramagnetism.

(iii) Ferrimagnetism:

The substances in which the magnetic moments of the domains are aligned in parallel and antiparallel directions, in unequal numbers, are said to have ferrimagnetism. Examples include (magnetite) , ferrites such as .

Ferrimagnetic substances are weakly attracted by a magnetic field as compared to ferromagnetic substances. On heating, these substances become paramagnetic.


Schematic alignment of magnetic moments in ferrimagnetic substances

(iv) Antiferromagnetism:

Antiferromagnetic substances have domain structures similar to ferromagnetic substances, but are oppositely oriented. The oppositely oriented domains cancel out each other՚s magnetic moments.


Schematic alignment of magnetic moments in antiferromagnetic substances

(v) 12 - 16 and 13 - 15 group compounds:

The 12 - 16 group compounds are prepared by combining 12, group 16 elements, and the 13 - 15 group compounds are prepared by combining group 13 and group 15 elements. These compounds are prepared to stimulate average valence of four as in Ge or Si. Indium (iii) antimonide , aluminium phosphide , and gallium arsenide are typical compounds of groups 13 - 15. semiconductors have a very fast response time and have revolutionised the designing of semiconductor devices. Examples of group 12 - 16 compounds include zinc sulphide , cadmium sulphide , cadmium selenide , and mercury (II) telluride . The bonds in these compounds are not perfectly covalent. The ionic character of the bonds depends on the electronegativities of the two elements.

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