Key difference - amorphous vs. crystalline solids
All materials can be classified into three main states based on their type of molecular aggregation; these categories are called solids, liquids, and gases. Gases and liquids are very different from solids in that they do not have a specific shape and take the shape of the container in which they are placed. In contrast to gases and liquids, solids have a certain three-dimensional shape with the most complex shape of a molecular aggregate. In addition, solids are relatively harder, denser and more dimensionally stable. In contrast to gases and liquids, solids are hardly affected by changes in temperature or pressure. In addition, solids have a wide range of mechanical and physical properties, including electrical conductivity, thermal conductivity , strength, hardness, toughness, etc. Because of these properties, solids are used in various applications in engineering, construction, automotive and manufacturing, etc. Solids mainly exist in two types: amorphous and crystalline. The main difference between amorphous and crystalline solids is that amorphous solids do not have an ordered structure, while crystalline solids have a highly ordered structure. In addition to this key difference, there are many other differences between these two types of solids.
This article explains
1. What are amorphous solids? - Definition, structure, properties, examples
2. What are crystalline solids? - Definition, structure, properties, examples
3. What is the difference between amorphous and crystalline solids?
What is an amorphous solid?
Amorphous solids are defined as solids that have no ordered structure. This means that the atoms or ions are arranged without a particular geometric shape. Certain amorphous solids may have some orderly arrangement, but it is only a few angstrom units. These ordered parts in amorphous solids are called crystallites. Because of their disorderly arrangement, amorphous solids are sometimes referred to as supercooled liquids .
The amorphous solids do not have sharp melting points , so the liquid conversion occurs over a range of temperatures. Properties such as electrical and thermal conductivity, mechanical strength and refractive index also do not depend on the direction of measurement; hence they are called isotropic.
Examples of amorphous solids include glass, solid polymers, and plastics.
What is a crystalline solid?
Crystalline solids are solids that have a highly ordered arrangement of atoms, ions or molecules in a well-defined three-dimensional structure. In addition, these solids are characterized by their hardness with sharp and high melting points.
In contrast to amorphous solids, crystalline solids show an anisotropic behavior when measuring their physical properties, which depend on the direction of measurement. Crystalline solids have certain geometric shapes that depend on the conditions during crystal growth.
Some examples of crystalline solids include diamond, sodium chloride, zinc oxide, sugar, etc.
Difference between amorphous and crystalline solids
Geometry / structure
Amorphous solids: Amorphous solids have no ordered structure; they lack any pattern or arrangement of atoms or ions or any geometric shape.
Crystalline solids: Due to the orderly arrangement of atoms or ions, crystalline solids have a specific and regular geometry.
Amorphous solids: Amorphous solids do not have a sharp melting point.
Crystalline Solids: Crystalline solids have a sharp melting point at which they turn into a liquid state.
Heat of fusion
Amorphous solids: Amorphous solids have no characteristic heat of fusion and are therefore regarded as supercooled liquids or pseudo solids .
Crystalline solids: Crystalline solids have a certain heat of fusion and are therefore considered to be true solids.
Anisotropy and isotropy
Amorphous solids: Amorphous solids are isotropic because they have the same physical properties in all directions.
Crystalline solids: Crystalline solids are anisotropic and therefore their physical properties differ in different directions.
Amorphous solids: Glass, organic polymers, etc. are examples of amorphous solids.
Crystalline solids: Diamond, quartz, silicon, NaCl, ZnS, all metallic elements such as Cu, Zn, Fe etc. are examples of crystalline solids.
Amorphous solids: Amorphous solids have covalently bound networks.
Crystalline Solids: Crystalline solids have covalent bonds, ionic bonds , van der Waals bonds, and metallic bonds.