The key difference between amorphous and crystalline solid is that the crystalline solids have an ordered long-range arrangement of atoms or molecules within the structure, whereas the amorphous solids lack ordered long-range arrangement.
We can classify solids into two as crystalline and amorphous depending on the atomic level arrangement. However, some solids are present in both crystalline and amorphous forms. Depending on the need, we can prepare both types separately.
What is Amorphous Solid?
Amorphous solid is a form of solid which lacks a crystalline structure. There, it does not have a long-range ordered arrangement of atoms, molecules, or ions within its structure. Moreover, glass, gels, thin films, plastics and nanomaterials are some examples of this type of solids.
We make glass primarily with sand (silica/ SiO2), and bases like sodium carbonate, and calcium carbonate. At high temperatures, these materials melt together, and when we cool them, rigid glass forms rapidly. Upon cooling, the atoms arrange in a disordered manner to produce glass; thus, we call it as amorphous. However, atoms can have a short-range order due to chemical bonding characteristics.
Likewise, we can prepare other amorphous materials also by rapidly cooling molten material. Amorphous solids do not have a sharp melting point. They liquefy over a broad range of temperatures. Amorphous solids like rubber are useful in tyre manufacturing. Glass and plastics are useful in making houseware, laboratory equipment etc.
What is Crystalline Solid?
Crystalline solids or crystals have ordered structures and symmetry. The atoms, molecules, or ions in crystals arranged in a particular manner; thus, have long-range order. In this type of solids, there is a regular, repeating pattern; therefore, we can identify a repeating unit.
By definition, a crystal is “a homogenous chemical compound with a regular and periodic arrangement of atoms. For instance, halite, salt (NaCl), and quartz (SiO2). But crystals are not restricted to minerals: they comprise most solid matter such as sugar, cellulose, metals, bones and even DNA.” C
Furthermore, crystals are naturally occurring materials on earth as large crystalline rocks such as quartz and granite. Sometimes, living organisms also form crystals. For example, calcite is a product by mollusks. There are water-based crystals in the form of snow, ice or glaciers.
Moreover, we can categorize crystals according to their physical and chemical properties. For instance, covalent crystals (e.g.: diamond), metallic crystals (e.g.: pyrite), ionic crystals (e.g.: sodium chloride) and molecular crystals (e.g.: sugar). Also, these crystals can have different shapes and colours. Therefore, they have an aesthetic value, and some people believe that they have healing properties; thus, they use these crystals to make jewellery.
What is the Difference Between Amorphous and Crystalline Solid?
Amorphous and crystalline solids differ from each other according to their chemical structures. Therefore, we can say that the key difference between amorphous and crystalline solid is that the crystalline solids have an ordered long-range arrangement of atoms or molecules within the structure, whereas the amorphous solids lack ordered long-range arrangement. Moreover, in crystalline solids, there is a repeating unit, which makes up the entire structure, but for amorphous solids, a repeating unit cannot be specified.
A further difference between amorphous and crystalline solids, crystalline solids have a sharp melting point, but amorphous solids don’t. Furthermore, crystalline solids are anisotropic (different properties in different directions), but amorphous solids are isotropic (properties are the same in all directions).
Summary – Amorphous vs Crystalline Solid
Solids are mainly in three types as amorphous, semi-crystalline and crystalline solids. The key difference between amorphous and crystalline solid is that the crystalline solids have an ordered long-range arrangement of atoms or molecules within the structure, whereas the amorphous solids lack ordered long-range arrangement.
1. Douglas, Ronald Walter, et al. “Amorphous Solid.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 22 Apr. 2016. Available here
2. Libretexts. “12.1: Crystalline and Amorphous Solids.” Chemistry LibreTexts, National Science Foundation, 26 Nov. 2018. Available here