🧪AP Chemistry Review
What Are The 4 Major Types of Solid Matter?
What Are The 4 Major Types of Solid Matter?
Solid Matter Types & Properties
There are 4 major types of solid: molecular, covalent network, ionic, and metallic. Let's dive in!
In AP Chemistry, you learn about 3 main states of matter: solids, liquids, and gases. While liquids and gases are certainly important, in this article we're going to be discussing the properties and classification of solids. In AP Chemistry, students compare several common classes of solids—molecular, covalent-network, ionic, and metallic—and relate each solid's properties to its bonding and structure. On the exam, you may need to use these ideas to explain or predict properties such as conductivity, melting point, hardness, brittleness, and solubility.
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1. Molecular Solids
Definition ⚛️
- Molecular solids are made of discrete molecules held together by intermolecular forces rather than by covalent bonds extending throughout the entire solid.
- Take ice, for example.
- Sure, each individual molecule is held together by covalent bonds, but the actual solid is created by hydrogen bonds connecting the molecules to each other.
Properties
- Intermolecular forces are weaker than ionic or covalent bonds, so molecular solids are relatively soft and flexible.
- This also means they tend to have low melting points.
- They do not conduct electricity because electrons are localized within individual molecules.
- Because the particles are separate molecules held together by intermolecular forces, molecular solids usually melt more easily than ionic or covalent network solids.
- Many polar molecular solids, such as sugar, are often soluble in water because they can form favorable intermolecular interactions with water; however, solubility depends on the specific substance and is not universal for all polar molecular solids.
- Keep in mind that the individual molecules don't break apart, only the intermolecular forces do!
- Key properties to know: low melting point, do not conduct electricity
🎥Live Stream Replay: Structures of Solids
2. Covalent Network Solids
Definition ⚛️
- Covalent network solids are held together by covalent bonds in a large network.
- They are different from molecular solids because atoms are covalently bonded to each other throughout the structure, not held together by intermolecular forces.
- Diamond and graphite are examples of covalent network solids made up of a network of carbon atoms:
Properties
- They are usually hard and brittle.
- Because atoms are connected by strong covalent bonds throughout the solid, covalent network solids generally have very high melting points.
- They usually don't conduct electricity because valence electrons are localized within covalent bonds.
- An exception to this is graphite, where only three of four valence electrons are involved in the covalent network and the fourth is delocalized.
- Because the bonding extends through the entire structure rather than between separate molecules, breaking or melting the solid requires disrupting many covalent bonds.
- Covalent-network solids are generally insoluble in water and most common solvents.
- Key properties to know: hard, high melting points, do not conduct electricity (in all but few cases)
🎥Live Stream Replay: Properties of Solids
⚡️Study Guide: Properties of Solids
3. Ionic Solids
Definition ⚛️
- Ionic solids are made up of oppositely charged ions held together by electrostatic attraction (a.k.a. ionic bonds).
- Electrostatic attraction just describes the attractive force between a positive charge and a negative charge.
- The strength of attraction in an ionic solid can be described qualitatively by Coulomb's law: the electrostatic force between two ions is proportional to (q1q2/r^2), where larger ionic charges and smaller distances between ions produce stronger attractions.
- The ions form a crystal lattice structure, seen in NaCl below:
Properties
- They're hard and brittle.
- They have high melting points because ionic bonds require a lot of energy to break.
- In solid form, ionic compounds are poor conductors.
- Because ions are locked into fixed positions in the crystal lattice, solid ionic compounds do not conduct electricity; when molten or dissolved, the ions are mobile and can carry charge.
- When molten, ionic compounds conduct electricity because the ions are free to move. When dissolved in water, many ionic compounds conduct electricity because the dissolved ions are mobile in solution.
- Not all ionic compounds are soluble, though, so keep those solubility rules in mind!
- Key properties to know: High melting points, conduct when dissolved BUT NOT AS SOLIDS!
🎥Live Stream Replay: Unit 2 Review
4. Metallic Solids
Definition ⚛️
- Metallic solids are metal atoms held together by metallic bonds.
- Metallic bonding is the sharing of a bunch of delocalized valence electrons that move freely throughout the solid (sometimes called the "sea of electrons" model).
- In a metallic solid, metal atoms are arranged in a lattice, and their valence electrons are delocalized throughout the structure.
Properties
- Metallic solids vary a lot when it comes to melting points. Tungsten has the highest melting point at 3422°C, whereas mercury has the lowest at -38.83°C.
- They are shiny, strong, and malleable.
- They can conduct electricity because of their delocalized electrons.
- Because valence electrons are delocalized throughout the metal lattice, metals conduct electricity and are malleable rather than brittle.
- Adding another element to a metallic solid can form an alloy with new properties.
Congratulations! You now know about the properties of the 4 major types of solids in AP Chemistry. In applying this knowledge on the exam, you may be asked to identify a solid by its properties and by connecting those properties back to its particle-level structure. For example, if I were to ask you what type of solid a compound was if it was brittle, melted at 1500 degrees, and conducted electricity when dissolved, you should know that this is an ionic solid. There are tons of practice questions out there just like this. Good luck!