How does antiferromagnetism differ from ferromagnetism in terms of magnetic domains?

In antiferromagnetism, the magnetic domains are aligned in opposite directions giving them a zero net magnetic moment, while in ferromagnetism, magnetic domains are aligned in the same direction giving them a high non-zero net magnetic moment.

An element has a body centred cubic structure with cell edge of 288 pm . The density of the element is 7 . 2 g cm - 3 . How many atoms are present in 208 g of the element?

Given, Edge lenght of the unit cell, a = 288 pm Density of the element, d = 7 . 2 g / cm 3 Mass of the element = 208 g For the BCC structure, Z = 2 Substituting the values in the expression d = Z × M a 3 × N A 7 . 2 g cm - 3 = 2 × M ( 288 × 10 - 10 cm ) 3 × ( 6 . 02 × 10 23 mol - 1 ) Atomic mass, M = 51 . 8 g mol - 1 We know that, 51 . 8 g of the element contains = 6 . 02 × 10 23 atoms Therefore, 208 g of the element contains = 6 . 02 × 10 23 51 . 8 × 208 atoms = 24 . 2 × 10 23 atoms.

What type of defect can arise when solid is heated?

When a solid is heated, vacancy defect is produced in the crystal. This is because, on heating, some atoms or ions leave the lattice site completely, therefore, some lattice sites become vacant. As a result of this defect, the density of the substance decreases.

(a) Aluminium crystallizes in a cubic close-packed structure. Its metallic radius is 125 pm . What is the length of the side of the unit cell? (b) Why is potassium chloride sometimes violet instead of pure white?

(a) It is given that aluminium crystallises in a cubic closed packed structure. Its metallic radius is 125 pm . For cubic close-packed structure, The edge length, a = 2 2 r Here, a is the edge length of the unit cell and r is the atomic radius. ∴ a = 2 2 × 125 = 354 pm (b) In presence of excess of potassium, Cl - ions leave their lattice sites creating anion vacancies. These vacancies are occupied by electrons given out by potassium and are known as F-centres. These F-centres are responsible for the violet colour of potassium chloride.

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The fraction of the total volume occupied by the atoms present in a simple cubic is

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