Metalloid

A metalloid is a chemical element with properties between those of metals and nonmetals. Some of these elements have metallic appearance—for example, lustre and metallic colour—while their chemical behaviour generally resembles that of nonmetals.

The alternative name used is "semimetal", though the term semimetal has a distinct technical meaning in physics. Elements commonly classified as metalloids include boron, silicon, germanium, arsenic, antimony, and tellurium. Some scientists include polonium and astatine, but these are not part of any formally established list.

Position in the periodic table

In the periodic table, metalloids occupy a zigzag boundary line running from boron to astatine, separating metals (left) from nonmetals (right). The boundary is gradual and imprecise, and different chemistry textbooks list different elements.

Properties

Metalloids are generally hard, brittle solids with metallic lustre. They conduct heat and electricity to varying degrees—typically as semiconductors, meaning electrical conductivity increases with temperature, unlike metals where it decreases. Chemically, they form covalent bonds and their oxides sometimes show amphoteric character, reacting with both acids and bases.

Uses

Silicon and germanium are the basis of semiconductor manufacturing: transistors, computer chips, and solar panels are made from them. Boron is used in heat-resistant glassware and some fertilizers. Arsenic and antimony are added to alloys to increase hardness and are also made into semiconductor compounds such as gallium arsenide.