Metalloids are a group of seven elements found between the metals and nonmetals on the periodic table. Metalloids share some characteristic properties of metals, such as metallic luster. They also share properties of nonmetals: they generally do not conduct electricity as well as metals and they tend to be brittle. Metalloids have electronegativity values that range between those of metals and nonmetals. This intermediate electronegativity is the reason that metalloids behave similarly to both metals and nonmetals.
Silicon and boron exhibit characteristic bonding behavior and have many practical applications due to the way they interact with oxygen. A silicon-silicon bond is not particularly strong. On the other hand, a silicon-oxygen bond is quite strong. A mineral that contains both silicon and oxygen is a silicate. Silicates can grow to be enormous molecules by alternating the silicon and oxygen atoms. Rocks, sand, and clay are mostly made up of silicates. Glass is another example of a silicate.A solid material with more than one possible structure is a polymorph. An example of a polymorph is silica. It forms the basis of many common minerals and can appear in different forms. Both sand and quartz are minerals that are made mostly of silica. The orthosilicate ion (SiO44–) is the basis of many silicate minerals. Orthosilicate has a tetrahedral shape consisting of one silicon atom and four oxygen atoms. Two orthosilicate ions can be connected by an oxygen atom, forming a disilicate ion (Si2O76–). The disilicate ions can be connected to each other to form a chain, a sheet, or a three-dimensional shape. When each orthosilicate ion connects to four other orthosilicate ions, a three-dimensional chain solid is formed. Because each orthosilicate is connected to four others by an oxygen atom, the net formula of the compound becomes silica (SiO2).