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We know three main phases of matter. Let's explore solids. Solids are a broad class of materials. They have diverse properties. Generally, they are rigid and have a fixed volume. Their atoms or molecules have powerful electrostatic interactions. We know that the particles pack tightly together. Let's look at the physical properties of the different types of solids.
Metals
Eighty percent of the periodic table is metals. The metal elements have five groups: alkali, alkaline-earth, transition metals, lanthanide, and actinides. A metal's physical properties are because of metallic bonding. In metallic bonding, the valence electrons delocalize. The delocalized electrons are strongly attracted to the metal nuclei.
The strong interactions induce solidity at room temperature. At the same time, they are malleable. The electrons are free to move. Bending a metal rearranges its electrons. The bonds do not break! Yet, some metals are hard to manipulate. A metal's hardness depends on the metallic bond's strength.
We use hard metals for construction. One example is steel, an alloy of iron and carbon. The hardness of the steel depends on the allotrope of iron. In metals, an allotrope is the same element with a different unit cell.
The delocalized electrons produce high thermal and electrical conductivity. In a metal, the atoms are tightly packed. As we heat the metal, the atoms' vibrational movements increase. The tight packing transfers the vibrational energy between atoms. The delocalized electrons create electrical conductivity. Electricity is the movement of electrons. Imagine a wire. When we add electrons to the wire, we generate a repulsive force. So, electrons to move from one end of the wire to the other. We created a current.
Ionic Crystals
Ionic bonds are the most secure chemical bonds. They produce a crystal lattice. The lattice has alternating cations and anions. The attractive forces between the ions generate significant lattice energies. It is difficult to break apart the bonds. So, they have high melting points and hardness. However, they can be very brittle. A large force will move the ions. If ions with the same charge come close together, the repulsive forces can break the bonds. So, the crystal cracks.
Ionic crystals are insulators. Their molecular geometry explains their lack of conductivity. In unit cells, the ions distribute into a regular pattern. The ions cannot move. So electrons cannot transfer from one ion to the next.
Covalent Networks
Covalent networks are crystals created by repeating covalent bonds. The most well-known example is diamonds. Covalent networks have a repeating VSEPR geometry. Covalent bonds are strong, so they have high melting points and hardness. The electrical conductivity depends on the type of bonding. Networks with only sigma bonds are insulators. But, pi bond networks are conductive. In a covalent network, pi bonds become delocalized. Just like in metals, the delocalized electrons move freely through the lattice. An example of a covalent network with pi bonds is graphite.
Molecular Crystals
Molecular solids are the weakest crystals. They hold together through dispersion forces, dipole-dipole interactions, or hydrogen bonding. Because intermolecular forces are weaker than chemical bonds, they have low melting points. It takes very little energy to separate the molecules. So, they are brittle.
Amorphous
Amorphous solids are a broad classification. They include polymers, glasses, rubbers, and plastics. In metals and crystals, the molecular geometry repeats. In contrast, amorphous solids do not have long-term repetition. The amorphous solids consist of metalloids or nonmetals.
Their most notable property is their glass transition point. The glass transition point is the temperature where an amorphous material transitions from brittle to malleable. We use some materials below their glass transition point. For example, the glass in your windows is amorphous silicon. You want hard windows. In contrast, the rubber in your car tires is above the glass transition temperature. It would be disastrous if your car tires became hard and brittle.
Nanomaterials
You may have heard about the growing field of nanotechnology. The size of a nanomaterial is . That's nanometers. At that scale, the size of the molecule limits the wavelength of the electrons. We call this limiting quantum confinement. The confined electrons have unusual behavior. So, nanomaterials have unique properties.
