The Chemistry of Solids: Classification, Properties, and Examples

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Ch.12 - The Chemistry of Solids

Classification of Solids

Solids are a fundamental state of matter characterized by fixed shape and volume. They are classified based on the arrangement of their constituent particles and the nature of their bonding.

Crystalline Solids: Atoms, ions, or molecules are arranged in a highly ordered and repeating pattern throughout the solid. This regularity leads to well-defined shapes and distinct melting points.
Amorphous Solids: Particles are randomly arranged with no discernible long-range order. These solids lack a sharp melting point and often soften over a range of temperatures.

Example: Olive oil hardens over a range of temperatures, indicating it is an amorphous solid.

Types of Solids and Their Properties

Solids can be further classified based on the nature of their smallest units and the forces holding them together.

Solid Type	Smallest Unit	Electrostatic Forces	Properties	Examples
Ionic Solid	Ions	Attraction between positive and negative ions	Hard, brittle, high melting point, conducts electricity when molten or dissolved	NaCl, AlF3, CaCO3
Molecular Solid	Molecules	Intermolecular forces (e.g., hydrogen bonding, dipole-dipole, London dispersion)	Soft, low melting point, does not conduct electricity	CO2, I2, H2O
Covalent Network Solid	Atoms	Covalent bonds	Very hard, high melting point, usually does not conduct electricity	Diamond, graphite, SiO2
Metallic Solid	Metal atoms	Metallic bonds (pooling of electrons)	Shiny, malleable, conducts electricity, variable melting points	Na, Ti, steel, bronze
Amorphous Solid	Atoms, ions, molecules, or polymers (plastics)	Any of the above	Soft, irregular texture, melts over a range of temperatures, no distinct melting point	Glass, plastics, hardened olive oil

Additional info: Table entries inferred and expanded for completeness.

Electrostatic Forces in Solids

The nature of the electrostatic forces within a solid determines its physical properties.

Ionic Solids: Electrostatic attraction between oppositely charged ions.
Molecular Solids: Intermolecular forces such as hydrogen bonds, dipole-dipole, and London dispersion forces.
Covalent Network Solids: Strong covalent bonds between atoms throughout the structure.
Metallic Solids: Metallic bonding, where electrons are delocalized and shared among metal atoms.

Example: The major electrostatic force within an ammonia molecule (NH3) is a covalent bond.

Practice: Classification and Identification

Identify the ionic solid: Among Cl2, H2Te, AlF3, and C (graphite), AlF3 is the ionic solid.
Olive oil as a solid: As it hardens over a range of temperatures, olive oil is best described as an amorphous solid.
Compound A: Hard, non-conductive, and melts at 1400ºC. This is characteristic of a covalent network solid.

Classification of Common Solids

Substance	Classification
Steel	Alloy (Metallic Solid)
CO2	Molecular Solid
Graphite	Covalent Network Solid
CaCO3	Ionic Solid
Bronze (Cu and Sn alloy)	Alloy (Metallic Solid)

Additional info: Table entries inferred for clarity and completeness.

Key Terms and Definitions

Crystalline Solid: A solid with a regular, repeating arrangement of particles.
Amorphous Solid: A solid with a random, non-repeating arrangement of particles.
Ionic Solid: A solid composed of ions held together by electrostatic forces.
Molecular Solid: A solid composed of molecules held together by intermolecular forces.
Covalent Network Solid: A solid where atoms are connected by covalent bonds in a continuous network.
Metallic Solid: A solid composed of metal atoms with delocalized electrons.
Alloy: A mixture of metals, often with improved properties compared to pure metals.

Formulas and Equations

While the chemistry of solids is often described qualitatively, some relevant equations include:

Lattice Energy (for Ionic Solids):
Melting Point Trends: Generally, stronger electrostatic forces (ionic or covalent network) lead to higher melting points.

Summary Table: Properties of Solid Types

Solid Type	Conductivity	Hardness	Melting Point
Ionic	Conducts when molten or dissolved	Hard, brittle	High
Molecular	Non-conductive	Soft	Low
Covalent Network	Non-conductive (except graphite)	Very hard	Very high
Metallic	Conductive	Malleable	Variable
Amorphous	Non-conductive	Soft, irregular	No distinct melting point

Additional info: Table expanded for academic completeness.