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Questions and Answers
What is the main feature of the structure of fullerenes?
Which fullerene is known as the most stable allotrope among fullerenes?
Which of the following is an application of fullerenes?
How are fullerenes typically prepared?
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What characteristic shape does C70 fullerene resemble?
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Which characteristic is true for crystalline solids?
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Which statement accurately describes amorphous solids?
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Which of the following pairs represents isomorphous substances?
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What distinguishes polymorphous solids from other forms of solids?
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Which property do crystalline solids possess that amorphous solids do not?
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Which type of solid has an irregular shape and no definite geometry?
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When cut, how do crystalline solids behave compared to amorphous solids?
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What is a common example of a polymorphous substance?
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Which of the following crystal systems has a maximum of three planes and three axes?
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What is true about the angles in a cubic crystal system?
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Which crystal system is characterized by $a eq b eq c$ and $eta eq 90^{ ext{°}}$?
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Which crystal system is represented by the lattice type that has $a=b eq c$ and angles $eta = 90^{ ext{°}}$, $ heta = 120^{ ext{°}}$?
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Which of the following is an example of a face-centered cubic structure?
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In which crystal system can you find a maximum symmetry of nine planes and thirteen axes?
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Which crystal system has the least number of planes and axes?
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Which of the following is NOT a characteristic of the tetragonal crystal system?
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What structural feature of ice makes it less dense than liquid water?
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Which of the following statements about ionic solids is true?
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What happens to the structure of ice when it melts?
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What is meant by the term 'tetrahedral void' in a crystal lattice?
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In a close-packed structure, how does the number of octahedral voids compare to the number of constituent particles?
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Why are ionic solids considered brittle?
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What defines the concept of 'packing in solids'?
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What distinguishes the voids in a close-packed structure?
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What happens to the stability of a crystal due to the presence of holes from missing ions?
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Which of the following is a characteristic of Frenkel defect?
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What is the consequence of a Frenkel defect on the dielectric constant of a crystal?
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In the context of ionic compounds, which condition favors the occurrence of Frenkel defect?
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What defines a substitution impurity defect?
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Which of the following materials is an example of an interstitial impurity defect?
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How does the presence of interstitial defects affect the electrical properties of crystals?
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What type of solid is characterized by electrical conductivity due to free electrons?
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Study Notes
Solids
- A solid is a form of matter with a definite shape and volume, meaning it is rigid and does not flow.
Types of Solids
-
Crystalline Solids: Constituent particles (atoms, ions, or molecules) are arranged in a definite, repeating pattern.
- Isomorphous Forms: Two or more substances with the same crystal structure. Examples: NaF and MgO (1:1 atom ratio), Cr2O3 and Fe2O3 (2:3 atom ratio).
- Polymorphous/Allotropic Forms: A single substance that crystallizes in two or more forms under different conditions. Examples: Carbon (graphite and diamond), Sulfur (rhombic and monoclinic).
- Amorphous Solids/Pseudo Solids/Super-cooled Solids: Appear solid but lack a well-defined crystalline structure. Examples: Glass, plastic, rubber, butter, starch, cellulose, proteins.
Crystalline vs. Amorphous Solids
| Property | Crystalline Solids | Amorphous Solids |
|---|---|---|
| Geometry | Definite geometry | No definite geometry |
| Shape | Regular | Irregular |
| Melting Point | Sharp melting point | No sharp melting point |
| Solid Type | True solids | Pseudo solids/Super-cooled liquids |
| Particle Arrangement | Long-range order | Short-range order |
| Cleavage | Clean cleavage when cut | Irregular surface when cut |
| Directional Properties | Anisotropic (different properties in different directions) | Isotropic (same properties in all directions) |
Fullerenes
- Discovery: Third crystalline allotrope of carbon discovered by K.E. Smalley, R.F. Curl, and H.W. Kroto. Awarded the 1996 Nobel Prize in Chemistry.
- Composition: C2n (where n>30)
- Preparation: Evaporation of graphite using a powerful laser.
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Structure:
- All carbon atoms are equivalent and undergo sp2 hybridization.
- Each carbon atom forms three sigma bonds with other carbon atoms.
- Delocalized electrons give the molecule aromatic character.
- C60 allotrope (Buckyball) is most stable, with 12 five-membered rings and 20 six-membered rings.
- C70 fullerene resembles a rugby ball, containing 12 five-membered rings and 25 six-membered rings.
-
Applications:
- K3SC60 behaves as a superconductor below 18 K.
- Fullerene and graphite tubes are called nanotubes.
- Used for high-strength materials, conductors, semiconductors, and molecular sensors.
Bravais Lattices
- Fourteen possible arrangements of lattice points in three-dimensional space.
Crystal Systems
| Sr. No. (No. Space Latice) | Crystal System | Lattice Type | Edge Length | Angles | Example | Maximum Symmetry |
|---|---|---|---|---|---|---|
| 1 (3) | Cubic | Simple/Primitive | a=b=c | α = β = γ = 90° | CsCl | Nine planes, Thirteen axes, One center |
| Body centered | a=b=c | α = β = γ = 90° | Li, Cr, CsCl | |||
| Face centered | a=b=c | α = β = γ = 90° | NaCl, Cu, Al, Ca, Ni | |||
| 2 (2) | Tetragonal | Primitive | a=b ≠ c | α = β = γ = 90° | SnO2 | Five planes, Five axes |
| Body centered | a=b ≠ c | α = β = γ = 90° | TiO2, CaSO4 | |||
| 3 (4) | Orthorhombic | Primitive/Simple | a ≠ b ≠ c | α = β = γ = 90° | Rhombic sulfur | Three planes, Three axes |
| Body centered | a ≠ b ≠ c | α = β = γ = 90° | KNO3 | |||
| Face centered | a ≠ b ≠ c | α = β = γ = 90° | BaSO4 | |||
| End centered | a ≠ b ≠ c | α = β = γ = 90° | MgSO4.7H2O | |||
| 4 (2) | Monoclinic | Primitive/Simple | a ≠ b ≠ c | α = γ = 90°, β ≠ 90° | Monoclinic S | One plane, One axis |
| End centered | a ≠ b ≠ c | α = γ = 90°, β ≠ 90° | Na2SO4.10H2O | |||
| 5 (1) | Triclinic | Primitive | a ≠ b ≠ c | α ≠ β ≠ γ ≠ 90° | K2Cr2O7, H3BO3 | No planes, No axes |
| 6 (1) | Hexagonal | Primitive | a=b ≠ c | α = β = 90°, γ = 120° | ZnO, BeO, CaS, SnS, Graphite | Seven planes, Seven axes |
Ionic Solids
- Formed by molecules with positively charged, small cations and negatively charged, larger anions.
- Strong electrostatic forces of attraction between nearest neighbor ions.
- Hard due to strong inter-particle attraction.
- Brittle because layers of ions slip and repel under stress.
Ice
- Less dense than liquid water due to its hexagonal, three-dimensional crystal structure formed by hydrogen bonds.
- Structure of liquid water and solid ice are similar.
- Melting of ice breaks some hydrogen bonds, and water molecules occupy empty spaces, collapsing the hexagonal structure.
- This leads to higher density in liquid water, making ice float.
Packing in Solids
- Packing: The space occupied by constituent particles in a unit cell.
- Void: Unoccupied space in a unit cell.
Types of Voids
-
Tetrahedral Voids: Formed when a sphere in the second layer rests on the hollow in three spheres of the first layer.
- Surrounded by four neighbors in a tetrahedral arrangement.
- Number of tetrahedral voids is double the number of constituent particles.
-
Octahedral Voids: Formed when three touching spheres in the second layer rest on the hollow in three spheres of the first layer.
- Surrounded by six neighbors in an octahedral arrangement.
- Number of octahedral voids is the same as the number of constituent particles.
- Presence of voids lowers the crystal's:
- Density
- Stability
- Lattice energy
- Does not affect the dielectric constant.
Interstitial Defect (Frenkel Defect)
- Discovered by Frenkel in 1926.
- Occurs when a cation or anion leaves its regular site and occupies an interstitial position.
Conditions Favoring Frenkel Defect
- Crystal structure has low coordination number.
- Anions are significantly larger than cations.
Consequences of Frenkel Defect
- Does not alter density.
- Responsible for electrical conductivity in crystals.
- Responsible for diffusion in solids.
- Decreases crystal stability.
- Increases dielectric constant of the crystal.
Schottky Defect
- Occurs when a pair of oppositely charged ions (cation and anion) are missing from their lattice sites.
- Affects density by reducing it.
Impurity Defect
- Occurs when a regular cation is replaced by a different cation, or excess cations occupy interstitial positions.
Types of Impurity Defets
- Substitution Impurity Defect: Impurity cation replaces a regular cation. Example: Brass (formed by substituting zinc for copper in a 1:3 ratio).
- Interstitial Impurity Defect: Impurity cation occupies an interstitial position. Example: Stainless steel (formed by introducing carbon atoms as impurities).
Electrical Properties of Solids
- Based on electrical conductivity, solids are categorized as:
- Metals: Good conductors of heat and electricity due to free electrons. Conductivity: 10^4 - 10^7 ohm^-1 m^-1. Examples: Na, Al, Cu.
- Nonmetals: Poor conductors of heat and electricity. Conductivity: 10^-10 - 10^-20 ohm^-1 m^-1. Examples: S, P, I.
- Semiconductors: Conductivity is between metals and nonmetals. Examples: Si, Ge.
Conductivity in Solids
- Metals: Delocalized electrons can easily move and carry charge.
- Nonmetals: No free electrons; charge carriers are limited, leading to low conductivity.
- Semiconductors: Valence electrons can be excited to the conduction band, increasing conductivity with temperature.
Band Theory
- Explains the electrical properties of solids by describing the energy levels of electrons in a crystal lattice.
- Conduction band: Contains electrons free to move and conduct electricity.
- Valence band: Contains electrons bound to atoms and cannot conduct.
- Energy gap: Separates the conduction band from the valence band.
Semiconductor Types
- Intrinsic semiconductors: Pure semiconductors with a small energy gap. Examples: Si, Ge.
- Extrinsic semiconductors: Semiconductors with impurities added to control conductivity. Examples: n-type and p-type semiconductors.
- n-type semiconductors: Contain impurities with extra electrons in the conduction band. Examples: P-doped Si.
- p-type semiconductors: Contain impurities with fewer electrons than the host, creating "holes" in the valence band. Examples: B-doped Si.
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Description
Test your understanding of solids with this quiz that covers the definitions and differences between crystalline and amorphous solids. Explore examples and properties associated with each type of solid. Perfect for students studying material science or chemistry.
