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Diode is a combination of n- type and p- type semiconductors. It is used as a rectifier.

(a) Cubic close packing: When a third layer is placed over the second layer in a manner that the octahedral voids are covered by the spheres, a layer different from the first (A) and second (B) is obtained. If we continue packing in this manner we get the cubic close packing.

Hexagonal close packing: When the third layer is placed over the second layer in a way that the tetrahedral voids are covered by the spheres, a 3D close packing is produced where spheres in each third or alternate layers are vertically aligned. If we continue packing in this order we get hexagonal close packing.

(b) Unit cell: It is the smallest 3D dimensional portion of a complete space lattice, which when repeated over and over again in different directions from the crystal lattice.

Crystal lattice – it is a regular orientation of particles of a crystal in a 3D space.

(c) Octahedral void – it is a void surrounded by 6 spheres.

Tetrahedral void – it is a void surrounded by 4 spheres.

(i) Coordination number is the number of nearest neighbours of a particle.

(ii) 

(a) coordination number =12

(b) coordination number = 8

The space between valence band and conduction band represent energies forbidden to electrons are called forbidden zone.

Correct answer is: (A) In metals, the forbidden zone is very small and in insulators, the forbidden zone is very large.

1. In metallic solids, the lattice points are occupied by positive metal ions and a cloud of electrons pervades the space.

2. They are hard and have high melting point.

3. Metallic solids possess excellent electrical and thermal conductivity. They possess bright lustre. 

4. Examples – Metals and metal alloys Cu, Fe, Zn, Ag, Ay, Cu – Zn etc.

In a solid, the constituent particles are very closely – packed. Hence, the forces of attraction among these particles are very strong, that is why they are rigid.

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Lattice point : A position occupied by a crystal constituent particle like an atom, ion or a molecule in the crystal lattice is called lattice point or lattice site.

OR 

Any point at the intersection of the lines in the unit cell occupied by a constituent particle like an atom, an ion or a molecule in the crystalline solid is called a lattice point.

Piezo electricity is the appearance of an electrical potential across the sides of a crystal. When you subject it to mechanical stress. The word piezo electricity means electricity resulting from pressure and latent heat. Even the inverse is possible which is known as inverse piezo electric effect.

Correct answer is: (B) a = b = c, \(\alpha\) = \(\beta\) = \(\gamma\) = 90\(^\circ\) 

Correct answer is: (D) 8

Correct answer is: (B) tetrahedral

Correct answer is: (D) all of these

Correct answer is: (D) 4 NaCl units

Schottky defect

I. It occurs due to missing of equal no of cations and anions from lattice point.

II. It decreases the density of the crystal.

III. It occurs in compounds with high Co-ordination number.

             OR

It occurs in compounds in which cations and anions are of similar size.

Examples: NaCl, KCl, KBr, Ag Br CsCl.

Frankel defect

I. It occurs due to missing of cations from their lattice point and occupies interstitial sites

II. It does not decrease the density of the crystal.

III. It occurs in compounds with low Co-ordination number.

               OR

It occurs in compounds in which cations and anions differ in their size to a large extent.

Examples: ZnS, AgCl, AgBr, Agl.

 Rubber and quartz glass are examples of amorphous solids.

Silver (Ag) and copper (Cu) have cubic close packed structure.

Given: Atoms C and D form fcc lattice.

C is present at corners of the cube.

D is at the faces of the cube.

To find: Formula of the compound

Calculation: As C is present at the 8 corners of the cube, number of atoms of C in the unit cell\(=\frac{1}{8}\times8=1\)

As D atoms are present at the face centres of the 6 faces of the cube, the number of atoms of D in the unit cell =\(=\frac{1}{2}\times6=3\)

\(\therefore\) Ratio of atoms C : D = 1 : 3.

Ans: The formula of the compound is CD₃.

Given: Elements A and B form bcc lattice.

Element A occupies body centre position and B is at the corner.

To find: Formula of the compound Coordination numbers of A and B

Calculation: As atoms B are present at the 8 corners of the cube, number of atoms of B in the unit cell =\(\frac{1}{8}\times8=1\)

As atoms A are present at the body centre, number of atoms of A in the unit cell = 1

\(\therefore\) Ratio of A : B = 1 : 1

\(\therefore\) Formula of the compound = AB

Coordination number of A occupying body centre position = 8

Coordination number of B at corners of the cube = 8

Ans: The formula of the compound is AB.

Coordination number of each A and B is 8.

The anionic vacancies occupied by unpaired electrons. 

F-centers impart colour to the crystals (Eg. NaCl toYellow, KCl to violet) due to excitation of these electrons by absorbing energy from the visible light falling on the crystals. 

Correct answer is: (D) Common salt

Correct answer is: (D) Molecular

Correct answer is: (A) Solid changes into liquid on heating to its melting point.

Correct answer is: (D) 6

Correct answer is: (B) sp²

Correct answer is: (A) 74%

Total volume of unit cell = 8\(\sqrt{8}r^3\)

Volume occupied = \(\cfrac{16}{3}\pi r^3\)

\(\therefore\) Packing efficiency =\(\cfrac{16}{3}\pi r^3\)\(\times\)\(\cfrac{1}{8\sqrt{8}r^3}\times100\)

= 74.0 %

Correct answer is: (B) LiF

Correct answer: (B) 8

Correct answer: (A) 68%

The percentage of total space filled by the particles in a crystal. 

Example: Packing efficiency of BCC structure = 68%.

Correct answer is: (A) 8

Correct answer is: (C) \(\cfrac{\sqrt{3}a}{2}\)

The Co-ordination No. of cation and anion in Caesium Chloride is 8 and 8.

Let the number of Ni²⁺ . Then the number of Ni³⁺ ion will be = (0.96 – x). 

Total number of cation, = 2 x + 3 (0.96 – x) 

= 2x + 2.88 – 3x 

= ( – x) + 2.88

Number of anions O2- ( – 2) x 1 = -2. Number of cations = Number of anions – x + 2.88 2

– x = – 2.88 + 2

x = 0.88

 % of Ni as Ni² = \(\frac{0.08}{0.96}\times 100\) = 91.66% 

Number of Ni³⁺ ion will be = 0.96 – x 

= 0.96 – 0.88 = 0.08 

% of Ni as Ni³⁺ =   \(\frac{0.08}{0.96}\times 100\)  = 8.3 %

In square close packing , each atom is in contact with four neighbouring atoms, so its coordination number is 4.

Correct answer is:  (B) \(\cfrac{4}{\sqrt{2}}r\)

Let the atoms N in cep = x
No of tetrahedral voids = 2x
As \(\frac { 1 }{ 3 }\) rd of the tetrahedral voids are occupied by atoms M,
Hence, no. of atoms of M = \(\frac { 2x }{ 3 }\)
Ratio of M:N = 20 : \(\frac { 2x }{ 3 }\) = 2:3
Hence formula of compound is M₂ N₃

Correct answer: (D) 2 and 4

i. Silicon dioxide is fused with sodium oxide and boron oxide to form an optically transparent material known as glass. The colour of glass is due to addition of a trace amount of transition metal oxide.

ii. Different types of glass are manufactured by changing its composition. Almost eight hundred different types of glasses are manufactured. Quartz glass is obtained from only silicon dioxide.

iii. Pyrex glass is obtained by fusing together 60 to 80% SiO₂, 10 to 25% B₂O₃ and remaining amount of Al₂O₃.

iv. When 75% SiO₂ is fused with 15% Na₂O and 10% CaO, sodalime glass is obtained.

v. Red glass contains trace amount of gold and copper. Yellow glass contains UO₂.

vi. Blue glass contains CoO or CuO. Green glass contains Fe₂O₃ or CuO.

Amorphous solids are those solids in which the constituent particles may have a short range order, have irregular shape and isotropic in nature. They do not show clean cleavage. They do not have sharp melting points and do not have definite heat of fusion.

Examples: glass, plastics and rubber etc.

Amorphous solids: Polyurethane, teflon, cellophane, polyvinyl chloride, fibre glass. Crystalline solids: Benzoic acid, potassium nitrate, copper, naphthalene.

1. -Crystalline solids are also known as true solids and amorphous solids are also known as pseudo solids or supercooled liquids.
2. So Polyurethane is an amorphous solid.
3. Naphthalene is a crystalline solid.
4. Benzoic acid is a crystalline solid.
5. Teflon is an amorphous solid.
6. Potassium nitrate is a crystalline solid.
7. Cellophane is an amorphous solid.
8. Polyvinyl chloride is an amorphous solid.
9. Fiberglass is an amorphous solid.
10. Copper is a crystalline solid.

The defect due to irregularity in a complete line, i.e., a row of lattice points of constituent particles is called line defect.

Vacancy defect.

The defect may arise due to the heat absorbed by the crystals from the surrounding or due to the presence of impurities in the crystals and also due to the irregularities in the arrangement of constituent particles. When the rate of crystallisation is fast, more defects are present. When the rate of crystallisation is slowest, the defects are minimized. The physical and chemical properties of crystalline solids are affected due to presence of crystal defects

Any deviation or irregularity from the perfectly ordered arrangement of constituent particles in crystal is called crystal imperfection or defect.

i. The coordination number of constituent particle of the crystal lattice is the number of particles surrounding a single particle in the crystal lattice. 

ii. In case of ionic crystals, coordination number of an ion in the crystal is the number of oppositely charged ions surrounding that ion. 

iii. The stoichiometry and the size of the cation and anion determines the structure of ionic compounds. 

iv. In ionic solids, the bigger ions (usually anions) form close packed structure and smaller ions (usually cations) occupy the voids. If the latter ion is small enough then tetrahedral voids are occupied; but if it is bigger, then octahedral voids are occupied. Generally, for an ionic crystalline structure to be stable, there is definite radiusratio (r⁺ /r^- ) limit for a cation to fit perfectly in the lattice of anions. This also defines the coordination number of the cation. 

v. The limiting values of r⁺/r^- for the coordination number and the hole occupied by the cation are given in the following table:

i. The stoichiometry and the size of the cation and anion determines the structure of ionic compounds.

ii. Smaller cations occupy tetrahedral voids and bigger cations occupy octahedral voids or cubic voids.

iii. The coordination number of the ion also determines the geometry of the unit cell.

iv. The ratio of the radius of the cation (r⁺ ) to the radius of the anion (r^- ) is the radius ratio \(\left(\cfrac{r^+}{r^-}\right)\). For a given coordination number, the radius ratio has a limiting value.

v. The ionic structure is unstable when the radius ratio is less than the expected value.

vi. By using radius ratio rule, the structures of ionic solids can be predicted. This rule is not applicable to covalent compounds.

(1) Coordination number : The number of the closest neighbouring constituent particles like atoms, ions or molecules which are in contact with a particular particle or an atom in the crystal lattice is called coordination number of that particle.

(In the crystal lattice, all atoms may have same or different coordination numbers.)

(2) The magnitude of the coordination number is a measure of compactness of spheres in close-packed structures.

(3) The higher the coordination number, the closer are the spheres to each other.