Quiz: NCERT Class 12 Chemistry - Unit 1 (The Solid State)

NCERT Class 12 Chemistry - Unit 1: The Solid State

Introduction to Solid State

  • Solids are characterized by a fixed shape, volume, and a regular arrangement of particles.
  • Crystalline solids: The particles are arranged in a regular, repeating pattern, resulting in distinct edges and faces (e.g., salt, sugar, metals).
  • Amorphous solids: The particles are arranged irregularly (e.g., glass, rubber).

Types of Crystals

  • Ionic crystals: Formed by electrostatic forces between oppositely charged ions. They are hard, brittle, and have high melting points (e.g., NaCl, MgO).
  • Covalent crystals: Formed by covalent bonds between atoms, resulting in a three-dimensional network (e.g., diamond, graphite).
  • Metallic crystals: Consist of metal atoms surrounded by a sea of delocalized electrons, which allow for electrical conductivity (e.g., copper, iron).
  • Molecular crystals: Held together by intermolecular forces such as Van der Waals forces or hydrogen bonds (e.g., ice, dry ice).

Properties of Crystalline Solids

  • Definite geometric shape: Crystals have sharp edges and fixed angles between faces.
  • Anisotropy: Physical properties (e.g., refractive index, electrical conductivity) vary in different directions.
  • Melting point: Crystalline solids have a sharp, well-defined melting point, unlike amorphous solids, which melt over a range of temperatures.
  • Cleavage: Crystalline solids break along definite planes (cleavage planes), while amorphous solids fracture irregularly.

Crystal Lattice and Unit Cell

  • Crystal lattice: A three-dimensional arrangement of points (atoms, ions, or molecules) in space.
  • Unit cell: The smallest repeating unit in a crystal lattice that defines its structure.
  • Types of unit cells:
    • Simple cubic (SC): Each unit cell has one atom at each corner.
    • Body-centered cubic (BCC): One atom at the center and at the corners.
    • Face-centered cubic (FCC): Atoms at the corners and the centers of each face.

Packing Efficiency

  • Packing efficiency refers to the fraction of space occupied by the particles in a unit cell.
  • Simple cubic: Packing efficiency = 52%.
  • Body-centered cubic (BCC): Packing efficiency = 68%.
  • Face-centered cubic (FCC): Packing efficiency = 74%.
  • Higher packing efficiency indicates a more tightly packed arrangement of particles.

Types of Defects in Crystals

  1. Point defects: Imperfections at a single point in the crystal lattice.

    • Vacancy defect: A lattice point is missing an atom/ion.
    • Interstitial defect: An extra particle occupies a space between lattice points.
    • Frenkel defect: A smaller ion moves from its normal position to an interstitial site.
    • Schottky defect: Both a cation and an anion are missing from the lattice, maintaining overall charge neutrality.

  2. Line defects: Defects along a line, such as dislocations.

    • Edge dislocation: A defect where an extra half-plane of atoms is inserted into a crystal.
    • Screw dislocation: A defect in which the crystal structure is twisted along a line.

  3. Surface defects: Defects occurring at the surface of the crystal, such as grain boundaries.

X-ray Diffraction

  • X-ray diffraction (XRD) is a technique used to study the arrangement of atoms in crystalline solids.
  • When X-rays are directed at a crystal, they are diffracted, and the resulting pattern is analyzed to determine the structure of the crystal.

Electrical and Magnetic Properties

  • Electrical properties: Solids can be classified as conductors (e.g., metals), insulators (e.g., ceramics), or semiconductors (e.g., silicon).
  • Magnetic properties:
    • Diamagnetic: Weakly repelled by a magnetic field (e.g., graphite, water).
    • Paramagnetic: Weakly attracted to a magnetic field (e.g., aluminum).
    • Ferromagnetic: Strongly attracted to a magnetic field and can be magnetized (e.g., iron).

Applications of Crystalline Solids

  • Semiconductors: Used in electronics, computers, and solar cells.
  • Materials with high strength: Like diamond, which is used in cutting tools.
  • Conductors: Used in electrical wiring (e.g., copper, gold).
  • Magnets: Used in motors and generators (e.g., iron, cobalt).

These brief notes cover the key concepts of The Solid State in Class 12 Chemistry. It helps in understanding the classification of solids, their properties, and applications, essential for exams like NEET and IIT-JEE.


 Test your understanding of "The Solid State" with this quiz designed for NEET and IIT-JEE aspirants.

1. Which of the following is an example of a crystalline solid?
a) Glass
b) Plastic
c) Sodium chloride
d) Rubber

2. In a face-centered cubic (FCC) unit cell, what is the number of atoms per unit cell?
a) 1
b) 2
c) 4
d) 6

3. Which type of defect occurs when a cation leaves its lattice site and occupies an interstitial site?
a) Schottky defect
b) Frenkel defect
c) Vacancy defect
d) Substitutional defect

4. The coordination number of a particle in a body-centered cubic (BCC) structure is:
a) 4
b) 6
c) 8
d) 12

5. Which of the following statements about amorphous solids is correct?
a) They have sharp melting points.
b) They are isotropic in nature.
c) They possess a regular arrangement of atoms.
d) They exhibit long-range order.

6. Calculate the edge length of a face-centered cubic unit cell if the radius of the atom is 140 pm.
a) 280 pm
b) 396 pm
c) 560 pm
d) 280√2 pm

7. Which of the following solids exhibits electrical conductivity in the molten state but not in the solid state?
a) Metallic solids
b) Ionic solids
c) Covalent solids
d) Molecular solids

8. In hexagonal close packing (HCP), the packing efficiency is approximately:
a) 52%
b) 68%
c) 74%
d) 100%

9. The number of octahedral voids present per sphere in a close-packed structure is:
a) 1
b) 2
c) 4
d) 6

10. Anisotropy in crystals is due to:
a) Random arrangement of particles
b) Ordered arrangement of particles
c) Different arrangements of particles in different directions
d) Isotropic behavior

Answer Key

  1. c) Sodium chloride
  2. c) 4
  3. b) Frenkel defect
  4. c) 8
  5. b) They are isotropic in nature.
  6. c) 560 pm
  7. b) Ionic solids
  8. c) 74%
  9. a) 1
  10. c) Different arrangements of particles in different directions

Additional Quiz: NCERT Class 12 Chemistry - Unit 1 (The Solid State)

1. The structure of diamond is:
a) Hexagonal close-packed (HCP)
b) Cubic close-packed (CCP)
c) Face-centered cubic (FCC)
d) Network covalent

2. What is the ratio of the radius of the atom (r) to the edge length (a) in a body-centered cubic (BCC) unit cell?
a) 32\frac{\sqrt{3}}{2}
b) 24\frac{\sqrt{2}}{4}
c) 34\frac{\sqrt{3}}{4}
d) 12\frac{1}{\sqrt{2}}

3. If the radius of an atom in a close-packed arrangement is 125 pm, what is the edge length of the unit cell for FCC?
a) 250 pm
b) 353.55 pm
c) 500 pm
d) 707 pm

4. Which type of solids have a high melting point and are usually brittle?
a) Ionic solids
b) Metallic solids
c) Covalent solids
d) Molecular solids

5. Identify the type of defect shown when an equal number of cations and anions are missing from the crystal lattice:
a) Schottky defect
b) Frenkel defect
c) Interstitial defect
d) Substitutional defect

6. The cubic close packing (CCP) arrangement has what percentage of packing efficiency?
a) 52%
b) 68%
c) 74%
d) 100%

7. In a simple cubic lattice, how many unit cells share one corner atom?
a) 2
b) 4
c) 6
d) 8

8. A compound is formed by two elements A and B. A atoms form the FCC lattice, and B atoms occupy all tetrahedral voids. What is the formula of the compound?
a) AB
b) AB2
c) A2B
d) AB4

9. The void fraction in a body-centered cubic (BCC) structure is approximately:
a) 32%
b) 26%
c) 48%
d) 23%

10. Graphite exhibits which type of bonding?
a) Ionic and covalent
b) Covalent and van der Waals
c) Metallic and covalent
d) Ionic and metallic

Answer Key

  1. d) Network covalent
  2. c) 34\frac{\sqrt{3}}{4}
  3. b) 353.55 pm
  4. a) Ionic solids
  5. a) Schottky defect
  6. c) 74%
  7. d) 8
  8. b) AB2_2
  9. a) 32%
  10. b) Covalent and van der Waals                                                                                                                  
More Quiz: NCERT Class 12 Chemistry - Unit 1 (The Solid State)

1. Which of the following is not a characteristic of ionic solids?
a) High melting points
b) Electrical conductivity in solid state
c) Hard and brittle
d) Solubility in polar solvents

2. In a hexagonal close-packed (HCP) structure, the number of nearest neighbors of each atom is:
a) 6
b) 8
c) 10
d) 12

3. The number of atoms present per unit cell in a simple cubic structure is:
a) 1
b) 2
c) 4
d) 8

4. If the radius ratio of a cation and an anion in an ionic solid is between 0.414 and 0.732, what type of void does the cation occupy?
a) Octahedral
b) Tetrahedral
c) Cubic
d) Trigonal

5. Which of the following statements about metallic solids is incorrect?
a) They are good conductors of heat and electricity.
b) They have high tensile strength.
c) They are brittle in nature.
d) They exhibit metallic luster.

6. In a crystal lattice, the void spaces in simple cubic packing amount to:
a) 48%
b) 52%
c) 68%
d) 74%

7. A compound crystallizes in a structure where the cations occupy 50% of the octahedral voids. What is the formula of the compound?
a) AB
b) AB2
c) A2B
d) AB3

8. The term "coordination number" in a crystal refers to:
a) The number of unit cells sharing one atom
b) The number of atoms surrounding a given atom in a crystal lattice
c) The number of atoms in a unit cell
d) The number of voids per unit cell

9. Which of the following defects increases the density of a crystal?
a) Schottky defect
b) Frenkel defect
c) Substitutional defect
d) Interstitial defect

10. In a crystal lattice of sodium chloride (NaCl), each Na^+ ion is surrounded by how many Cl^ ions?
a) 4
b) 6
c) 8
d) 12

Answer Key

  1. b) Electrical conductivity in solid state
  2. d) 12
  3. a) 1
  4. a) Octahedral
  5. c) They are brittle in nature.
  6. b) 52%
  7. b) AB2_2
  8. b) The number of atoms surrounding a given atom in a crystal lattice
  9. d) Interstitial defect
  10. b) 6


NEET Objective Chemistry

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