Question

What kinds of particles are present in each of the four main classes of crystalline solids?

Short answer

Atomic, molecular, ionic, and covalent network solids contain atoms, molecules, ions, and covalently bonded atoms, respectively.

Step-by-step solution

Understanding Crystalline Solids

Crystalline solids are solids that have a well-defined, repeating pattern of molecules or atoms. They are classified into four main types based on the nature of their constituent particles and the forces that hold them together.

Identifying Atomic Solids

In atomic solids, the particles present are individual atoms. These are held together by covalent, metallic, or weak dispersion forces, depending on the type of atomic solid. Examples include noble gases in solid form (only at low temperatures) and metals.

Exploring Molecular Solids

Molecular solids are composed of molecules. The forces holding these molecules together are usually van der Waals forces, hydrogen bonds, or dipole-dipole interactions. Examples include ice (H₂O), dry ice (CO₂), and sugar.

Investigating Ionic Solids

Ionic solids consist of ions arranged in a lattice structure. They are held together by strong ionic bonds between oppositely charged ions. Examples include common table salt (NaCl) and calcium fluoride (CaF₂).

Understanding Covalent Network Solids

Covalent network solids are made up of atoms connected by covalent bonds in a continuous network. These are typically very hard and have high melting points. Examples include diamond (a form of carbon) and quartz (SiO₂).

Key concepts

Atomic Solids

In atomic solids, the fundamental building blocks are individual atoms. These solids are characterized by how these atoms interact and bind with one another.
For instance, atomic solids consisting of noble gases are held together by weak dispersion forces. Such solids are usually found in solid form only at very low temperatures, since the forces between their atoms are relatively weak.
In the case of metals, the atoms are held together by metallic bonds. These bonds allow the delocalization of electrons, which contributes to the conductivity and malleability of metals. Overall, atomic solids can vary greatly in properties based on the type of atomic interactions involved.

• Noble gas atomic solids: Weak dispersion forces.
• Metal atomic solids: Stronger metallic bonds.

Molecular Solids

Molecular solids are made up of molecules held together by intermolecular forces. These forces are generally weaker than the bonds found in ionic or covalent network solids, making molecular solids softer and having lower melting points.
Common intermolecular forces include van der Waals forces, hydrogen bonds, and dipole-dipole interactions. For example, ice (solid water) is held together by hydrogen bonds, while carbon dioxide in its solid form (dry ice) is held together by van der Waals forces.

• Examples: Ice (H₂O), Dry ice (CO₂).
• Forces: Van der Waals, hydrogen bonds, dipole-dipole.

Ionic Solids

Ionic solids consist of a lattice of ions, where each positive ion is surrounded by negative ions and vice versa. This arrangement is strongly held together by ionic bonds, which are powerful attractions between opposite charges.
These bonds give ionic solids distinct properties such as high melting points and the ability to conduct electricity when melted or dissolved in water. A classic example of an ionic solid is common table salt (NaCl). In such solids, the rigid lattice structure contributes to their brittleness.

• Examples: Table salt (NaCl), Calcium fluoride (CaF₂).
• Properties: High melting points, electrical conductivity in solution.

Covalent Network Solids

Covalent network solids are distinguished by a continuous network of covalent bonds. These solids contain atoms linked throughout the solid by covalent bonds, creating a very robust and stable structure.
Consequently, covalent network solids are incredibly hard and have very high melting points. One of the most well-known examples is diamond, a form of carbon where each atom is covalently bonded to four others in a 3D lattice. Another example is quartz, a crystalline form of silicon dioxide (SiO₂). These properties make covalent network solids crucial in applications requiring extreme durability and heat resistance.

• Examples: Diamond (carbon), Quartz (SiO₂).
• Properties: Extreme hardness, high melting points.