Solids: A Last-Minute Review 🚀

Hey there, future AP Chem superstar! Let's solidify your understanding of solids (pun intended 😉) with this focused review. We'll hit the key points, make connections, and get you feeling confident for the exam. Let's dive in!

Types of Solids: An Overview

Solids are categorized by the forces holding their atoms/molecules together. Here's a quick rundown:

• Ionic Solids: Held by electrostatic forces between cations and anions. Think strong attractions! 🧂
• Metallic Solids: Held by metallic bonds between metal atoms. Electrons are like a 'sea' that flows freely. ✨
• Covalent Network Solids: Held by a vast network of covalent bonds. Super strong and hard! 💎
• Molecular Solids: Held by weak intermolecular forces (IMFs). Relatively soft and low melting point. 🧊

Amorphous vs. Crystalline Solids

Amorphous Solids

• No long-range, repeating structure. Think of them as disorganized! 🥴
• Formed by rapid cooling.
• Examples: glass, rubber, gum.

Image Courtesy of OpenTextBC

Crystalline Solids

• Particles arranged in a repeating pattern. Very organized! 🤓
• Have a definite melting point.
• More ductile and less brittle than amorphous solids.

Crystal Lattice & Unit Cell

• Crystal Lattice: The geometrical pattern of points on which crystalline solids are arranged.
• Unit Cell: The smallest repeating unit of the crystal lattice. Think of it as the basic building block. 🧱

Image Courtesy of Expii

Metallic Solids

• Metal atoms held together by metallic bonds.
• Cations in a 'sea' of delocalized valence electrons. 🌊

Animation Courtesy of DocSity

Properties of Metallic Solids

• Good conductors of electricity ⚡ (due to delocalized electrons).
• High melting and boiling points. 🌡️
• Shiny appearance. ✨
• Malleable and ductile. 🔌

Alloys

• Mixtures of two or more elements with metallic properties.
• Substitutional Alloy: Atoms of one element replace atoms of another in the lattice.
• Interstitial Alloy: Smaller atoms fit into the spaces between larger atoms.

Image Courtesy of the University of North Florida

Ionic Solids

• Cations and anions held together by strong electrostatic forces.
• High melting points due to strong attractions. 🔥

• Brittle due to attractive and repulsive interactions.
• Conduct electricity only when molten or in solution (when ions are mobile).
• Ions occupy the lattice points.

Molecular Solids

• Atoms or molecules held together by weak IMFs.
• Strong intramolecular forces (covalent bonds) but weak intermolecular forces.

Properties of Molecular Solids

• Low melting and boiling points (weak IMFs). 🧊
• Brittle and hard (weak IMFs are easily broken).
• Poor conductors of heat and electricity (no free electrons). 🚫🔌

Covalent Network Solids

• Atoms held together by a large network of covalent bonds. 💪
• Much harder and have higher melting points than molecular solids. 🔥
• Examples: diamond and graphite (both made of carbon).

Image Courtesy of JidOnline

Graphite

• Carbon atoms in layers of rings.
• $sp^2$ hybridized with pi bonds.
• Delocalized electrons make it a good conductor. ⚡
• Strong bonds within layers, weak bonds between layers.
• Soft because layers can slide. ✏️

Diamond

• Hardest naturally occurring substance. 💎
• $sp^3$ hybridized.
• Insulator. 🚫

Comparing Solids: A Quick Reference Chart

Final Exam Focus

High-Priority Topics

• Types of Solids: Understand the differences in bonding and properties.
• Coulomb's Law: Connect it to ionic solid properties.
• Intermolecular Forces: Relate them to molecular solid properties.
• Covalent Network Solids: Know the key examples (diamond and graphite) and their unique properties.

Common Question Types

• Multiple Choice: Identifying types of solids based on properties or bonding.
• Free Response: Comparing and contrasting properties of different solids, explaining trends using Coulomb's law or IMFs.

Last-Minute Tips

• Review the chart above to quickly compare properties.
• Focus on the connections between bonding, IMFs, and properties.
• Don't overthink it! You've got this! 💪

Practice Question

Practice Questions

Multiple Choice Questions

1. Which of the following solids is likely to have the highest melting point? (A) $CO_2(s)$ (B) $NaCl(s)$ (C) $H_2O(s)$ (D) $C(diamond)(s)$

2. A solid is a poor conductor of electricity, brittle, and has a high melting point. Which type of solid is it most likely to be? (A) Metallic (B) Ionic (C) Molecular (D) Covalent network

3. Which type of solid is characterized by delocalized electrons? (A) Ionic (B) Molecular (C) Metallic (D) Covalent network

Free Response Question

Consider the following substances: $KCl(s)$, $Ar(s)$, $SiO_2(s)$, and $Cu(s)$.

(a) Identify the type of solid for each substance.

(b) Rank the substances in order of increasing melting point. Justify your ranking based on the types of forces holding the solids together.

(c) Explain why $Cu(s)$ is a good conductor of electricity, while $KCl(s)$ is not.

FRQ Scoring Breakdown:

(a) (4 points)

• 1 point for correctly identifying $KCl(s)$ as an ionic solid.
• 1 point for correctly identifying $Ar(s)$ as a molecular solid.
• 1 point for correctly identifying $SiO_2(s)$ as a covalent network solid.
• 1 point for correctly identifying $Cu(s)$ as a metallic solid.

(b) (3 points)

• 1 point for correct ranking: $Ar(s) < KCl(s) < Cu(s) < SiO_2(s)$.
• 1 point for correct justification of $Ar(s)$ having the lowest melting point due to weak IMFs (LDFs).
• 1 point for correct justification of $SiO_2(s)$ having the highest melting point due to strong covalent network bonds.

(c) (2 points)

• 1 point for stating that $Cu(s)$ has delocalized electrons, which can move freely and conduct electricity.
• 1 point for stating that $KCl(s)$ has fixed ions in a lattice and cannot conduct electricity in the solid phase.

That's it! You've got a solid understanding of solids now. Go ace that exam! 💯