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Questions and Answers
Which of the following is an amorphous solid?
Which of the following is an amorphous solid?
- Silicon carbide
- Chrome alum (correct)
- Graphite
- Quartz glass
Which of the following statements is not true for amorphous solids?
Which of the following statements is not true for amorphous solids?
- They become crystalline on heating at certain temperatures
- Amorphous solids can be molded by heating
- They may become crystalline on keeping for long
- They are anisotropic in nature (correct)
What is isomorphism?
What is isomorphism?
- The process of heating to alter the crystal structure
- Two or more substances having the same crystal structure (correct)
- A substance that exists in multiple forms
- Different substances with different crystal structures
What defines polymorphism?
What defines polymorphism?
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What is allotropy?
What is allotropy?
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Which characteristic properly describes solids?
Which characteristic properly describes solids?
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What distinguishes crystalline solids from amorphous solids?
What distinguishes crystalline solids from amorphous solids?
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Which of the following is NOT true about amorphous solids?
Which of the following is NOT true about amorphous solids?
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Which of the following is a characteristic of crystalline solids?
Which of the following is a characteristic of crystalline solids?
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Which of these materials is categorized as a crystalline solid?
Which of these materials is categorized as a crystalline solid?
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Study Notes
Solid State Overview
- Solids have a regular and repeated arrangement of atoms, categorized into crystalline and amorphous types.
- Crystalline solids possess a long-range order, while amorphous solids have a short-range order.
Characteristics of Solids
- Hardness: Solids are hard and not easily compressible.
- Rigidity: Fixed shape and volume, maintaining their form under pressure.
- Fixed Composition: Defined mass, volume, and density.
- Particle Arrangement: Particles are fixed in position with vibrational motion.
- Intermolecular Forces: Strong attractive forces lead to short intermolecular distances.
Crystalline vs. Amorphous Solids
| Crystalline Solid | Amorphous Solid |
|---|---|
| Regular geometric shapes | Irregular shapes |
| Sharp melting points | Melt over a range of temperatures |
| True solids | Pseudo solids |
Types of Solids
- Crystalline Solids: Examples include ice, salt (NaCl), and metals (sodium, gold, copper).
- Amorphous Solids: Examples include glass, plastic, and rubber.
Distinct Characteristics
- Amorphous solids can transform into crystalline structures upon heating or aging.
- For crystalline solids, isotropic nature is a significant characteristic, contrasted with the anisotropic properties of amorphous solids.
Isomorphism and Polymorphism
- Isomorphism: Occurs when different substances have the same crystal structure, e.g., NaF and MgO.
- Polymorphism: Different crystalline forms of the same substance exist under varying conditions, e.g., D-quartz and p-quartz for silica.
Allotropes
- Allotropes refer to different structural forms of the same element, a specific case of polymorphism.
Unit Cells in Crystals
- Primitive Cells: Simple cubic unit cells with atoms only at the corners.
- Non-Primitive Cells: Include atoms at corners, faces, and center.
Types of Non-Primitive Unit Cells
- Body-Centered: Atoms at all corners and center.
- Face-Centered: Atoms at all corners and center of faces.
- End-Centered: Atoms at corners and two opposite faces.
Packing Efficiency
- Calculated using the formula for volume:
- Body Centered Cubic (BCC) packing efficiency is 68%.
- Face Centered Cubic (FCC) packing efficiency is 74%.
Types of Crystalline Solids
| Type | Properties | Examples |
|---|---|---|
| Ionic | Hard and brittle, high melting points, poor conductors in solid state | NaCl, CaF |
| Covalent | Very hard, high melting points, poor electrical conductors | Diamond, Silica |
| Molecular | Soft, low melting points, good thermal and electrical conductors | Ice, Benzoic acid |
Crystal Systems
| Crystal System | Length | Angles |
|---|---|---|
| Cubic | a = b = c | α = β = γ = 90° |
| Rhombohedral | a = b = c | α = β = γ ≠90° |
| Tetragonal | a = b ≠c | α = β = γ = 90° |
| Hexagonal | a = b ≠c | α = β = 90°, γ = 120° |
| Orthorhombic | a ≠b ≠c | α = β = γ = 90° |
| Monoclinic | a ≠b ≠c | α = β = 90°, γ ≠90° |
| Triclinic | a ≠b ≠c | α ≠β ≠γ ≠90° |
Key Relationships
- Molar mass, density, and edge length of a unit cell are interrelated through mathematical expressions that can be used for calculations in quantitative assessments.
Important Formulas
- Packing efficiency = (Volume of spheres / Total volume) x 100.
- Void space = 100% - Packing efficiency.
Questions for Understanding
- Identify primitive unit cells based on edge length and angle variations.
- Recognize the Bravais lattices corresponding to different crystal systems.
These notes provide a comprehensive overview of solid-state chemistry, emphasizing key concepts and definitions essential for understanding.
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