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Aluminium crystallizes in a cubic close-packed structure. Its metallic radius is 125 pm.
(a) What is the length of the side of the unit cell?
(b) How many unit cells are there in 1.00 cm3 of aluminium?


Given, radius of atom (r) = 125 pm

(a) For ccp structure, we know that,


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

We know that two Na+ 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 of the Sr2+ ions 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 – 3 mol Since, 100 moles of NaCl produces cation vacancies after doping = 10 –3 mol

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


therefore, total cationic vacancies
=10-5 x Avogadro's number
=10-5  x 6.023 x 1023
=6.023 x 10-18 vacancies
 

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Gold (atomic radius = 0.144 nm) crystallises in a face-centred unit cell. What is the length of a side of the cell?


Radius, r = 0.144 nm,
Unit cell is fcc, edge of unit cell, a = ?
In face centered unit cell, diagonal of face = 4r = a2
                                [∵ face diagonal = a2]

Therefore,       a=4r2 = 2r
                     
  = 2 × 1.4142 × 0.144 nm= 0.4073 nm.

Length of side of unit cell,
                   
a = 0.4073 nm.
                   
 
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Explain the following with suitable examples:
Paramagnetism

paramagnetism:

few substances like O2, Cu2+, Fe3+, Cr3+  are weekly attracted by a magnetic field.
These substabces are magnetised in a magnetic field in the same direction. When we remove magnetic field ,they lose their magnetism. paramagnetism is takes place due to presence of one or more unpaired electrons. These unpaired electron are attracted by the magnetic field.
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Explain the following with suitable examples:
Ferromagnetism.

Ferromagnetism: This is caused by particles arranged on lattice and the electrons with parallel spins. Iron, cobalt, nickel are ferromagnetic elements. It is a permanent property of material at a given temperature. The magnetic moments are aligned in same direction and due to this it gives rise to ferromagnetism. Unlike paramagnetic substances, ferromagnetic materials show permanent magnetism even when the magnetic field is removed. CrO2 is used to make magnetic tapes for use in audio-recording.

Ferromagnetism: This is caused by particles arranged on lattice and t
Fig.  Schematic alignments of magnetic moments in ferromagnetism.

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