मराठी
Maharashtra State BoardHSC Science (Computer Science) 12th Standard Board Exam
प्रश्नपत्रिका२७४
पाठ्यपुस्तक उत्तरे१०२९२
MCQ ऑनलाइन सराव परीक्षा६०
महत्वाचे प्रश्न आणि उत्तरे८३५६
संकल्पना स्पष्टीकरण आणि व्हिडिओ४५०
टाइम टेबल३२
अभ्यासक्रम

Overview of Solid State

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Topics

Estimated time: 62 minutes
Maharashtra State Board: Class 12

Definition: Crystalline solid

A solid in which the constituent particles are arranged in a regular and periodic three-dimensional pattern is called a crystalline solid.

Maharashtra State Board: Class 12

Definition: Amorphous solid

A solid in which the constituent particles are irregularly arranged and lack long-range order is called an amorphous solid.

Maharashtra State Board: Class 12

Definition: Ionic solid

A crystalline solid composed of oppositely charged ions held together by electrostatic forces of attraction is called an ionic solid.

Maharashtra State Board: Class 12

Definition: Molecular solid

A solid whose constituent particles are molecules held together by intermolecular forces is called a molecular solid.

Maharashtra State Board: Class 12

Definition: Metallic solid

A crystalline solid formed by metal atoms held together by metallic bonds due to the presence of delocalised electrons is called a metallic solid.

Maharashtra State Board: Class 12

Definition: Lattice

A regular three-dimensional geometrical arrangement of points in space representing the positions of particles in a crystal is called a lattice.

Maharashtra State Board: Class 12

Definition: Simple cubic unit cell (sc)

A unit cell in which particles are present only at the eight corners of a cube is called a primitive or simple cubic unit cell (sc).

\[a=2r\quad;\quad r=\frac{a}{2}\]

Maharashtra State Board: Class 12

Definition: Body-centred cubic unit cell (bcc)

A unit cell in which particles are present at the eight corners and one particle at the centre of the cube is called a body-centred cubic unit cell (bcc).

\[\sqrt3a=4r\quad;\quad r=\frac{\sqrt3a}{4}\]

Maharashtra State Board: Class 12

Definition: Face-centred cubic unit cell (fcc)

A unit cell in which particles are present at the eight corners and at the centre of each of the six faces of the cube is called a face-centred cubic unit cell (fcc).

\[\sqrt2a=4r\quad;\quad r=\frac{a}{2\sqrt2}\]

Definition: Coordination number

The number of nearest neighbouring particles surrounding a given particle in a crystal is called the coordination number.

Definition: Void space

The empty space present in a crystal lattice not occupied by particles is called void space.

Maharashtra State Board: Class 12

Formula: Volume of unit cell

Volume = a3

CBSE: Class 12

Formula: Density of unit cell

\[\rho=\frac{m\times n}{a^3}\]

Formula: Relation between molar mass and mass of one particle

\[m=\frac{M}{N_A}\]

Maharashtra State Board: Class 12

Formula: Density formula (in terms of molar mass)

\[\rho=\frac{nM}{a^3N_A}\]

Maharashtra State Board: Class 12

Formula: Volume of one sphere (particle)

\[V=\frac{4}{3}\pi r^3\]

Maharashtra State Board: Class 12

Formula: Packing efficiency formula

\[\text{Packing efficiency}=\frac{\text{Volume occupied by particles in unit cell}}{\text{Total volume of unit cell}}\times100\]

Maharashtra State Board: Class 12

Definition: Schottky defect

The defect in ionic solids where equal number of cations and anions are missing from their lattice sites is called Schottky defect.

Maharashtra State Board: Class 12

Definition: Frenkel defect

The defect in ionic solids where an ion leaves its normal lattice site and occupies an interstitial position is called Frenkel defect.

Maharashtra State Board: Class 12

Definition: impurity defect

The defect caused by the presence of foreign atoms in a crystal lattice is called impurity defect.

Definition: Conductor

A solid having high electrical conductivity is called a conductor.

Definition: Insulator

A solid having very low electrical conductivity is called an insulator.

Definition: Semiconductor

A solid having electrical conductivity intermediate between conductor and insulator is called a semiconductor.

Maharashtra State Board: Class 12

Definition: Paramagnetism

The magnetic property of a substance due to presence of unpaired electrons weakly attracted by magnetic field is called paramagnetism.

Maharashtra State Board: Class 12

Definition: Ferromagnetism

The magnetic property of a substance strongly attracted by magnetic field and retaining magnetism is called ferromagnetism.

Definition: Dopant

An impurity added to a semiconductor to increase its conductivity is called dopant.

Definition: Vacancy defect

The defect in which some lattice points are vacant due to missing atoms or ions is called vacancy defect.

Definition: Band gap

The energy difference between valence band and conduction band is called band gap.

Definition: Doping

The process of adding controlled impurity to increase conductivity of a semiconductor is called doping.

Definition: Valence band

The lower energy band filled with electrons is called valence band.

Definition: Conduction band

The highest energy band containing electrons in a solid is called conduction band.

Definition: Substitutional impurity defect

The defect in which impurity atoms replace host atoms at lattice sites is called substitutional impurity defect.

Definition: Interstitial impurity defect

The defect in which impurity atoms occupy interstitial spaces in the lattice is called interstitial impurity defect.

Maharashtra State Board: Class 12

Key Points: Classification of crystalline soli

Type of Crystalline Solid Constituent Particles Type of Bonding / Forces Main Properties Examples
Ionic Solids Cations and anions Electrostatic force of attraction (ionic bond) Hard and brittle; high melting points; non-conductors in solid state; conduct electricity when molten or dissolved in water NaCl, KCl, K₂SO₄, CaF₂
Covalent Network Solids Atoms Continuous covalent bonds (3D network) Very hard; very high melting and boiling points; poor conductors of electricity (except graphite) Diamond, SiO₂ (quartz), BN, SiC
Molecular Solids Molecules Weak intermolecular forces (dipole-dipole, London forces, hydrogen bonding) Soft; low melting points; poor conductors of electricity Ice (H₂O), CO₂, CH₄, NH₃
Metallic Solids Metal atoms (positive ions in sea of electrons) Metallic bond (delocalised electrons) Malleable, ductile; good conductors of heat and electricity Na, Fe, Cu, Ag, Au
Maharashtra State Board: Class 12

Key Points: Seven Crystal Systems and Bravais Lattices

S. No. Crystal System Axial Lengths (a, b, c) Axial Angles (α, β, γ) Types of Bravais Lattices (Unit Cells) Total Lattices
1 Cubic a = b = c α = β = γ = 90° (i) Simple (Primitive) (ii) Body-Centred (BCC) (iii) Face-Centred (FCC) 3
2 Tetragonal a = b ≠ c α = β = γ = 90° (i) Simple (Primitive) (ii) Body-Centred 2
3 Orthorhombic a ≠ b ≠ c α = β = γ = 90° (i) Simple (Primitive) (ii) Body-Centred (iii) Face-Centred (iv) Base-Centred 4
4 Monoclinic a ≠ b ≠ c α = γ = 90°, β ≠ 90° (i) Simple (Primitive) (ii) Base-Centred 2
5 Triclinic a ≠ b ≠ c α ≠ β ≠ γ ≠ 90° (i) Simple (Primitive) 1
6 Rhombohedral (Trigonal) a = b = c α = β = γ ≠ 90° (i) Simple (Primitive) 1
7 Hexagonal a = b ≠ c α = β = 90°, γ = 120° (i) Simple (Primitive) 1
Maharashtra State Board: Class 12

Key Points: Magnetic Properties of Solids

Type of Solid Electron Arrangement Behaviour in Magnetic Field Magnetic Nature Examples
Diamagnetic Solids All electrons are paired Weakly repelled by magnetic field No permanent magnetic moment; magnetism cancelled due to pairing of electrons N₂, F₂, NaCl, H₂O, Benzene
Paramagnetic Solids One or more unpaired electrons Weakly attracted by magnetic field Temporary magnetism; show magnetism only in presence of external magnetic field O₂, Cu²⁺, Fe³⁺, Cr³⁺
Ferromagnetic Solids Large number of unpaired electrons Strongly attracted by magnetic field Can be permanently magnetised; retain magnetism even after removal of field Fe, Co, Ni, Gd, CrO₂
Maharashtra State Board: Class 12

Key Points: Point Defects in Crystalline Solids

Main Type Sub-Type Description Effect on Density Electrical Neutrality Examples / Notes
Stoichiometric Defects Vacancy Defect Some lattice sites are vacant due to missing particles Decreases (mass decreases, volume same) Maintained Common in ionic solids
  Self-Interstitial Defect Extra particle occupies interstitial space Increases (mass increases, volume same) Maintained Seen in elemental solids
  Schottky Defect Equal number of cations and anions are missing from lattice sites Decreases Maintained NaCl, KCl, AgBr
  Frenkel Defect Ion leaves normal lattice site and occupies interstitial site No change Maintained ZnS, AgCl, AgBr
Impurity Defects Substitutional Impurity Foreign atom replaces host atom in lattice May change Maintained Brass (Cu–Zn alloy)
  Interstitial Impurity Foreign atom occupies interstitial space May change Maintained Stainless steel (Fe–C)
  Vacancy due to Aliovalent Impurity Different valency impurity creates vacancies to maintain neutrality Decreases Maintained Sr²⁺ added to NaCl
Non-Stoichiometric Defects Metal Deficiency Defect Missing metal ions; charge balanced by higher oxidation state Slight change Maintained NiO → Ni₀.₉₇O
  Metal Excess Defect (Interstitial) Extra metal ions occupy interstitial sites Increases Maintained ZnO
  Metal Excess Defect (F-centre) Anion vacancy occupied by electron No major change Maintained NaCl (yellow colour)
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