Study Guide : Unit 3 Part 2 Properties of Solids AP Chemistry

Properties of Solids

🧠 Concept Overview

Solids have a fixed shape and volume due to strong intermolecular forces. But types differ: IonicComposed of cations and anions held by electrostatic forces., MetallicMetal atoms bonded via delocalized electrons., Covalent NetworkAtoms bonded in a continuous 3D covalent network., and MolecularMolecules held together by weak IMFs like LDFs or H-bonds..

[ 🔍 Diagram: Solid types & bonding styles ]

⚗️ Types of Solids

Type	Particles	Bonding Type	Examples
Ionic	Cations & Anions	Electrostatic (Coulomb’s LawF = q₁q₂ / r² — Force increases with charge and decreases with distance.)	NaCl, MgO
Metallic	Metal atoms	Delocalized electrons (Metallic bondingElectrons flow in a 'sea', allowing conductivity and malleability.)	Fe, Cu, alloys
Covalent Network	Atoms	3D covalent network	Diamond, SiO2
Molecular	Molecules	IMFs: LDFWeak attractions from momentary dipoles., DipoleAttractions between polar molecules., H-bondingOccurs when H is bonded to N, O, or F.	I2, CO2

Coulomb’s Law: F = q₁q₂ / r² — Stronger when charges are high and ions are close.

⚡ Electrical Conductivity

• Ionic: Only conducts when molten or in solution
• Metallic: Always conducts
• Covalent: Usually doesn't (Graphite is an exception)
• Molecular: Does not conduct

Special Case: Graphite

Graphite is a covalent network with sp² hybridizedEach C atom makes 3 sigma bonds and has 1 delocalized π electron. carbon atoms. Layers of delocalized electrons allow conductivity.

🔩 Metallic Alloys

• Substitutional: Atoms of similar size replace each other (e.g., brass)
• Interstitial: Small atoms fill gaps in lattice (e.g., steel)
• Alloys are harder but less malleable and less ductile

🧬 Optional: Polymers & Biomolecules

• Polymers: Large molecules with IMFs (e.g., polyethylene)
• Kevlar: Strong polymer with hydrogen bonds
• Sugars: Crystalline due to OH groups
• Amino acids: Crystalline due to internal charges
• Proteins: Structure held by IMFs and folding

📊 Summary Table

Property	Ionic	Metallic	Covalent Network	Molecular
Melting Point	High	Varies	Very High	Low
Hardness	Brittle	Malleable	Very Hard	Soft
Conductivity	Only molten/solution	Yes	No (except graphite)	No

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