the conduction band of body centred cubic sodium (valence = 1) would be half filled
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1. Amorphous solids are the solids whose constituent particles are irreguraly arranged and have short range order. These solids are isotropic in nature and melt over a range of temperature. Therefore, amorphous solids are sometimes called pseudo solids or super cooled liquids. They do not have definite heat of fusion. When cut with a sharp-edged tool, they cut into two pieces with irregular surfaces. Examples of amorphous solids include glass, rubber, and plastic.
2. The arrangement of the constituent particles makes glass different from quartz. In glass, the constituent particles have short-range order, but in quartz, the constituent particles have long range order.
Quartz can be converted into glass by heating and then cooling it rapidly.
3. Amorphous solids: Polyurethane, teflon, cellophane, polyvinyl chloride, fibre glass
Crystalline solids: Naphthalene, benzoic acid, potassium nitrate, copper
4. (i) The number of nearest neighbours of any constituent particle present in the crystal lattice is called its coordination number.
(ii) The coordination number of atoms
(a) in a cubic close-packed structure is 12, and
(b) in a body-centred cubic structure is 8.
5. By knowing the density of an unknown metal and the dimension of its unit cell, the atomic mass of the metal can be determined.
Let ‘a’ be the edge length of a unit cell of a crystal, ‘d’ be the density of the metal, ‘m’ be the atomic mass of one atom of the metal and ‘z’ be the number of atoms in the unit cell.
Now, density of the unit cell =Mass of the unit cell/ Volume of the unit cell
d = z × m / a3 × NA……………………(i)
[Since mass of the unit cell = Number of atoms in the unit cell × mass of one atom and mass of one atom = atomic mass / NA]
[Volume of the unit cell = (Edge length of the cubic unit cell)3]
From equation (i), we have:
m = d × a3 × NA / z…………………….
2. The arrangement of the constituent particles makes glass different from quartz. In glass, the constituent particles have short-range order, but in quartz, the constituent particles have long range order.
Quartz can be converted into glass by heating and then cooling it rapidly.
3. Amorphous solids: Polyurethane, teflon, cellophane, polyvinyl chloride, fibre glass
Crystalline solids: Naphthalene, benzoic acid, potassium nitrate, copper
4. (i) The number of nearest neighbours of any constituent particle present in the crystal lattice is called its coordination number.
(ii) The coordination number of atoms
(a) in a cubic close-packed structure is 12, and
(b) in a body-centred cubic structure is 8.
5. By knowing the density of an unknown metal and the dimension of its unit cell, the atomic mass of the metal can be determined.
Let ‘a’ be the edge length of a unit cell of a crystal, ‘d’ be the density of the metal, ‘m’ be the atomic mass of one atom of the metal and ‘z’ be the number of atoms in the unit cell.
Now, density of the unit cell =Mass of the unit cell/ Volume of the unit cell
d = z × m / a3 × NA……………………(i)
[Since mass of the unit cell = Number of atoms in the unit cell × mass of one atom and mass of one atom = atomic mass / NA]
[Volume of the unit cell = (Edge length of the cubic unit cell)3]
From equation (i), we have:
m = d × a3 × NA / z…………………….
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