Types of Solids and How to Categorize Them

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. Ionic Solids Ionic solids form when electrostatic attraction causes anions and cations to form a crystal lattice. In an ionic crystal, each ion is surrounded by ions with an opposite charge. Ionic crystals are extremely stable because considerable energy is required to break ionic bonds. Metallic Solids The positively charged nuclei of metal atoms are held together by valence electrons to form metallic solids. The electrons are considered delocalized because they arent 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 are characterized by high thermal and electrical conductivity and are typically hard, shiny, and ductile. Examples: Almost all metals and their alloys, such as gold, brass, steel. Network Atomic Solids This type of solid is also known simply as a network solid. Network atomic solids are huge crystals consisting of atoms held together by covalent bonds. Many gemstones are network atomic solids. Examples: Diamond, amethyst, ruby. Atomic Solids Atomic solids form when weak London dispersion forces bind the atoms of cold noble gasses. Examples: These solids are not seen in everyday life since they require extremely low temperatures. An example would be solid krypton or solid argon. Molecular Solids Covalent molecules held together by intermolecular forces form molecular solids. While the intermolecular forces are strong enough to hold the molecules in place, molecular solids typically have lower melting and boiling points than metallic, ionic, or network atomic solids, which are held together by stronger bonds. Example: Water ice. Amorphous Solids Unlike all of the other types of solids, amorphous solids do not exhibit a crystal structure. This type of solid is characterized by an irregular bonding pattern. Amorphous solids may be soft and rubbery when they are formed by long molecules, tangled together and held by intermolecular forces. Glassy solids are hard and brittle, formed by atoms irregularly joined by covalent bonds. Examples: Plastic, glass.