Crystalline and Amorphous Solids, Classification of Solids, Key Features (For CBSE, ICSE, IAS, NET, NRA 2022)

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Solids Classification

  • A solid interface is defined as a small number of atomic layers that separate two solids in intimate contact with one another, where the properties differ significantly from those of the bulk material it separates.
  • Based on their crystal structures, solids can be classified into the following categories:
    • Crystalline solids
    • Amorphous solids
  • However, crystalline solids can be further classified into molecular, ionic, metallic, and covalent solids. A brief introduction to the classification of solids is provided in this article.

Classification of Solids – Crystalline and Amorphous Solids

An illustration detailing the classification of solids is provided below.

Classification of Solids

Classification of Solids – Crystalline and Amorphous Solids

What Are Crystalline Solids?

  • The solids featuring highly ordered arrangements of their particles (atoms, ions, and molecules) in microscopic structures are called crystalline solids.
  • These ordered microscopic structures make up a crystal lattice that accounts for the structure of the solid at any given point. Examples of crystalline solids include salt (sodium chloride) , diamond, and sodium nitrate.

What Are Amorphous Solids?

  • The solids in which the particles are not arranged in any specific order or the solids that lack the overall order of a crystal lattice are called amorphous solids.
  • The term β€˜amorphous’ , when broken down into its Greek roots, can be roughly translated to β€œwithout form” . Many polymers are amorphous solids. Other examples of such solids include glass, gels, and nanostructured materials.
  • An ideal crystal is defined as an atomic arrangement that has infinite translational symmetry in all the three dimensions, whereas such a definite definition is not possible for an ideal amorphous solid (a-solid) .

Key Features of Crystalline and Amorphous Solids


  • Crystalline Solids – True Solids
  • Amorphous Solids – Pseudo – Solids or super-cooled liquids


  • Crystalline Solids – Particles are arranged in a repeating pattern. They have a regular and ordered arrangement resulting in a definite shape.
  • Amorphous Solids – Particles are arranged randomly. They do not have an ordered arrangement resulting in irregular shapes

Melting Points

  • Crystalline Solids – They have a sharp melting point
  • Amorphous Solids – They do not have sharp melting points. The solid tends to soften gradually over a temperature range

Heat of Fusion

(The change in enthalpy when a substance is heated to change its state from solid to liquid.)

  • Crystalline Solids – They have definite heat of fusion.
  • Amorphous Solids – They do not have definite heat of fusion


  • Crystalline Solids – Anisotropic in nature. i.e.. , the magnitude of physical properties (such as refractive index, electrical conductivity, thermal conductivity etc.) is different along with different directions of the crystal.
  • Amorphous Solids – Isotropic in nature. i.e.. , the magnitude of the physical properties is the same along with all directions of the solid.

Cleavage Property

  • Crystalline Solids – When cutting with a sharp edge, the two new halves will have smooth surfaces
  • Amorphous Solids – When cutting with a sharp edge, the two resulting halves will have irregular surfaces


  • Crystalline Solids – They are rigid solids and applying mild forces will not distort its shape.
  • Amorphous Solids – They are not rigid, so mild effects may change the shape.


What is Meant by Crystalline Solids?


Crystalline solids consist of atoms, ions, and molecules arranged in a strongly ordered microscopic arrangement in consistent and repeated three-dimensional structures, forming a crystal lattice that stretches in any direction.

Is Wood Amorphous or Crystalline?


  • Crystalline solids are made of stone, wood, paper and cloth. Such solids consist of atoms arranged in a particular fashion.
  • The transition to liquid, called melting, is sharp and transparent as crystalline solids are heated. Amorphous solids are made of rubber, glass and Sulphur.

What Are the 7 Types of Crystals?


  • Seven crystal structures are available in total: triclinic, monoclinic, orthorhombic, tetragonal, trigonal, hexagonal, and cubic.
  • A family of crystals is determined by groupings of lattices and lines.

What Are Examples of Crystalline and Amorphous Solids?


  • The most common example of an amorphous solid is Glass. Gels, plastics, various polymers, wax, thin films are also good examples of amorphous solids.
  • This variation in characteristics of solids occurs due to the arrangement of their molecules.

What Are Two Examples of Amorphous Solids?


  • Unlike a crystalline solid, an amorphous solid is a solid that lacks an ordered internal structure.
  • Some examples of amorphous solids include rubber, plastic, and gels. Glass is a very important amorphous solid that is made by cooling a mixture of materials in such a way that it does not crystallize.

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