Metalloids are a group of chemical elements that have properties that are intermediate between those of metals and nonmetals. There is no standard definition of a metalloid, and there is no complete agreement on which elements are metalloids. However, it is generally agreed that there are at least six commonly recognized metalloids: boron, silicon, germanium, arsenic, antimony, and tellurium. Other elements that are sometimes classified as metalloids include bismuth, polonium, and astatine.

Some key properties of metalloids include:

• Appearance: Metalloids have a metallic appearance, but they are usually brittle and only mediocre electricity conductors.

• Chemical behavior: Chemically, metalloids usually behave as non-metals, but they have the ability to form metallic alloys.

• Semiconducting properties: Most metalloids tend to display semiconducting properties in at least one of their allomorphic modifications.

Metalloids have a variety of applications, including in alloys, catalysts, biological agents, glasses, flame retardants, optical storage and optoelectronics, semiconductors, pyrotechnics, and electronics.