Chapter 4 Crystal Structures-CET-0112-14 1

Focus on various solid materials: Metals, semiconductors, polymers, and nanomaterials.
Significance of solid classification: Key to understanding their physical properties and applications in technology.

Devices like computers and cell phones rely on specific physical properties of materials.
Integrated circuits are made using:
- Semiconductors (e.g., Silicon)
- Metals (e.g., Copper)
- Insulators (e.g., Hafnium Oxide)

Metallic Solids
- Held by a delocalized sea of valence electrons.
- Properties: Conduct electricity, strong but not brittle.
Ionic Solids
- Formed from the electrostatic attraction between cations and anions.
- Properties: Generally brittle, poor electrical conductors in solid state, but can conduct when molten or dissolved in water.
Covalent-Network Solids
- Held together by extensive networks of covalent bonds.
- Properties: Very hard, high melting points, poor conductors.
Molecular Solids
- Held together by intermolecular forces (dispersion, dipole-dipole, hydrogen bonds).
- Properties: Soft, low melting points.

High melting points due to strong ionic bonds.
Typically brittle and do not conduct electricity (only conduct when molten or in solution).
Electrolytes: Compounds that conduct electricity in aqueous solutions or molten states.

Ions in ionic solids are arranged in a well-defined crystal lattice.
Stability and strength of these lattices depend on ionic charge and size.
- Higher charge -> stronger bonds and higher melting points.

Common solubility patterns:
- Compounds with
  - NO and CH3COO: Soluble
  - Cl, Br, I: Soluble except with Ag+, Hg22+, and Pb2+

Formed by extensive covalent bonding that leads to unique properties like hardness and high melting points.
Examples include diamonds, silicon carbide, and quartz.

Consist of molecules held by weak intermolecular forces, leading to lower melting points.
Structure and bonding affect properties like melting points; symmetry in molecules contributes to packing efficiency.

Hydrogen Bonds: Strongest intermolecular force due to attraction between hydrogen and highly electronegative atoms (F, O, N).
Dipole-Dipole Forces: Occur in polar molecules due to partial charge attractions.
Dispersion Forces: Week forces that arise from temporary fluctuations in electron distribution.

Metals are solid at room temperature (except mercury), shiny, with high melting and electrical conductivity.
Properties include: Malleability, ductility, and high density.
Bonding arises from a 'sea' of delocalized electrons.

Common lattice types: primitive cubic, body-centered cubic, face-centered cubic.
Each structure is characterized by shared atoms across unit cells.

Types include:
- Substitutional alloys (similar atomic radii)
- Interstitial alloys (smaller atoms in gaps between larger atoms)
- Heterogeneous alloys (non-uniform distribution)

Common Alloys:
- Stainless steel (Fe, Cr, Ni)
- Bronze (Cu, Sn)
- Brass (Cu, Zn)

Dimension between 1-100 nm, where unusual properties emerge due to scale.
Applications include: Electronics, medical imaging, and chemical detection.
Quantum dots show peculiar optical properties, changing color with size due to varying band gaps.

Large molecules formed from repeated subunits (monomers).
Types: Thermoplastics, thermosetting plastics (hard, cannot be reshaped), and elastomers (rubber-like).

Addition Polymerization: Connecting monomers by opening double bonds.
Condensation Polymerization: Combining two monomers with the release of a small molecule (e.g., water).