The 4 Major Types of Solid Matter

Solid Matter Types & Properties

1. Molecular Solids

Definition 

• Molecular solids are made of molecules or atoms held together by intermolecular forces, not covalent bonds.
• 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.

Source: chemguide

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.
• Polar molecular solids, like sugar, will be soluble in water.
• 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

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 or molecules are covalently bonded to each other, not held together by intermolecular forces.
• Diamond and graphite are examples of covalent network solids made up of a network of carbon atoms:

Source: Science Media Group

Properties

• They are usually hard and brittle.
• Covalent bonds are very strong, so covalent network solids typically have the highest melting points out of all four types of solids.
• 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.
• They are insoluble in water.
• Key properties to know: hard, high melting points, do not conduct electricity (in all but few cases)

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 an ionic solid can be described by Coulomb's Law (Q = k(Q1Q2/r^2))
  • Essentially, high charge + small ions = high electrostatic force
• The ions form a crystal lattice structure, seen in NaCl below:

Source: Redefining Knowledge

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.
• When melted or dissolved in water, they will conduct electricity because they dissociate into individual ions that are free to move around.
• 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!

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 electron" model)
• The metal atoms have a uniform distribution.

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.
• Adding another element to a metallic solid can form an alloy with new properties.