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Solid – Definition, Examples, Classes, Types, and More

Solid Definition

A solid is a state of matter characterized by particles arranged such that their shape and volume are relatively stable.

Solid constituents tend to be packed together much closer than the particles in a gas or liquid. A solid has a rigid shape because the atoms or molecules are tightly connected via chemical bonds.

The bonding may produce either a regular lattice (as seen in ice, metals, and crystals) or an amorphous shape (as seen in glass or amorphous carbon). A solid is one of the four fundamental states of matter, liquids, gases, and plasma.

Solid-state physics and solid-state chemistry are two branches of science dedicated to studying solids’ properties and synthesis.

Examples of Solid


The matter with a defined shape and volume is solid. There are many examples:

  • A brick
  • A penny
  • A piece of wood
  • A chunk of aluminium metal (or any metal at room temperature except mercury)
  • Diamond (and most other crystals)

Examples of not solids include liquid water, air, liquid crystals, hydrogen gas, and smoke.

Classes of Solid

The different types of chemical bonds that join the particles in solids exert characteristic forces to classify solids. Ionic bonds (e.g. in table salt or NaCl) are strong bonds that often result in crystalline structures that may dissociate to form ions in water. Covalent bonds (e.g., in sugar or sucrose) involve the sharing of valence electrons. Electrons in metals seem to flow because of metallic bonding. Organic compounds often contain covalent bonds and interactions between separate portions of the molecule due to van der Waals forces.

Major classes of solid include:


  • Minerals natural solids form by geological processes. A mineral has a uniform structure.
  • Examples include diamond, salts, and mica.


  • Solid metals include elements (e.g., silver) and alloys (e.g., steel). Metals are typically complex, ductile, malleable, and excellent conductors of heat and electricity.


  • Ceramics are solids consisting of inorganic compounds, usually oxides. It tends to be hard, brittle, and corrosion-resistant.

Organic Solids

  • Organic solids include polymers, wax, plastics, and wood. Most of these solids are thermal and electrical insulators. They typically have lower melting and boiling points than metals or ceramics.

Composite Materials

  • Composite materials are those which contain two or more phases. An example would be a plastic containing carbon fibres. These materials yield properties not seen in the source components.


  • Semiconducting solids have electrical properties intermediate between those of conductors and insulators. The solids may be either pure elements, compounds, or doped materials.
  • Examples include silicon and gallium arsenide.


  • Nanomaterials are tiny solid particles at the nanometer size. These solids may display very different physical and chemical properties from large-scale versions of the same materials. For example, gold nanoparticles are red and melt at a lower temperature than gold metal.


  • Biomaterials are natural materials, such as collagen and bone, that are often capable of self-assembly.

The 6 Main Types of Solids


In the broadest sense, solids may be categorized as either crystalline solids or amorphous solids. Most specifically, scientists typically recognize six main types of solids, each characterized by specific properties and structures.

1. Ionic Solids

  • Ionic solids form when electrostatic attraction causes anions and cations to form a crystal lattice. In an ionic crystal, each ion surround by ions with an opposite charge. Ionic crystals are highly stable because considerable energy requires to break ionic bonds.

2. Metallic Solids

  • The positively charged nuclei of metal atoms are held together by valence electrons to form metallic solids.
  • The electrons consider “delocalized” because they aren’t bound to any particular atoms, as in covalent bonds. Delocalized electrons can move throughout the solid.
  • This is the “electron sea model” of metallic solids—positive nuclei float in a sea of negative electrons. Metals characterize by high thermal and electrical conductivity and are typically complex, shiny, and malleable.
  • Examples: All metals and their alloys, such as gold, brass, steel.

3. Network Atomic Solids

  • This solid is also known simply as a network solid. Network atomic solids are giant crystals consisting of atoms held together by covalent bonds.
  • Many gemstones are network atomic solids.
  • Examples: Diamond, amethyst, ruby.

4. Atomic Solids

  • Atomic solids form when weak London dispersion forces bind the atoms of cold noble gasses.
  • Examples: These solids did not see in everyday life since they require shallow temperatures. An example would be solid krypton or solid argon.

5. Molecular Solids

  • Covalent molecules held together by intermolecular forces form molecular solids.
  • While the intermolecular forces are strong enough to control the molecules in place, molecular solids typically have lower melting and boiling points than metallic, ionic, or network atomic solids held together by firmer bonds.
  • Example: Water ice.

6. Amorphous Solids

  • Unlike all of the other types of solids, amorphous solids do not exhibit a crystal structure. An irregular bonding pattern characterizes this solid.
  • Amorphous solids may be soft and rubbery when formed by long molecules, tangled together and held by intermolecular forces.
  • And also, glassy solids are hard and brittle, formed by atoms irregularly joined by covalent bonds.


Solids generally divide into three broad classes—crystalline, noncrystalline (amorphous), and quasicrystalline. Crystalline solids have a very high degree of order in a periodic atomic arrangement.

Practically all metals and many other minerals, such as typical table salt (sodium chloride), belong to this class. And also, noncrystalline solids are those in which atoms and molecules do not organize in a definite lattice pattern.

They include glasses, plastics, and gels. Quasicrystalline solids display novel symmetries in which the atoms arrange in a quasiperiodic fashion—i.e., in patterns that do not repeat at regular intervals.

They exhibit symmetries, such as fivefold symmetry, that forbid ordinary crystals. Quasicrystal structures are common in alloys in which aluminium combine with another metal, such as iron, cobalt, or nickel.

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