Amorphous vs Crystalline Solid
Solids can be classified into two as crystalline and amorphous depending on the atomic level arrangement. Some solids are present in both crystalline and amorphous forms. Depending on the need both types can be made separately.
Amorphous solid is a solid which lacks a crystalline structure. That is, it does not have long range ordered arrangement of atoms, molecules, or ions within the structure. Glass, gels, thin films, plastics and nano structures materials are some examples for amorphous solids. Glass is primarily made with sand (silica/ SiO2), and bases like sodium carbonate, and calcium carbonate. At high temperatures, these materials melt together, and when they are cooled, a rigid glass is formed rapidly. When cooling, the atoms are arranged in a disordered manner to produce glass; thus, it is referred to as amorphous. However, atoms can have a short-range order due to chemical bonding characteristics. Likewise, other amorphous materials can also be prepared by rapidly cooling molten material. Amorphous solids don’t have a sharp melting point. They liquefy over a broad range of temperature. Amorphous solids like rubber are used in tyre manufacturing. Glass and plastics are used in the making of house ware, laboratory equipment etc.
Crystalline solids or crystals have ordered structures and symmetry. The atoms, molecules, or ions in crystals are arranged in a particular manner; thus, have a long range order. In crystalline solids, there is a regular, repeating pattern; thus, we can identify a repeating unit. By definition, a crystal is “a homogenous chemical compound with a regular and periodic arrangement of atoms. Examples are 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.” Crystals are naturally occurring on earth as large crystalline rocks such as quartz, granite. Crystals are formed by living organisms too. For example, calcite is produced by mollusks. There are water-based crystals in the form of snow, ice or glaciers. Crystals can be categorized according to their physical and chemical properties. They are covalent crystals (e.g.: diamond), metallic crystals (e.g.: pyrite), ionic crystals (e.g.: sodium chloride) and molecular crystals (e.g.: sugar). Crystals can have different shapes and colors. Crystals have an aesthetic value, and it is believed to have healing properties; thus, people use them to make jewelry.
What is the difference between Amorphous Solid and Crystalline Solid?
• Crystalline solids have an ordered long range arrangement of atoms or molecules within the structure. But amorphous solids lack ordered long range arrangement. However, they may have a short range order due to chemical bonding.
• In crystalline solids, there is a repeating unit, which makes up the entire structure, but for amorphous solids, a repeating unit cannot be specified.
• When amorphous solids are heated and cooled slowly, they can become crystalline at some point.
• Crystalline solids have a sharp melting point, but amorphous solids don’t.
• Crystalline solids are anisotropic, but amorphous solids are isotropic.