Metalloid

Lore & Background

The term metalloid originally referred to nonmetals. Metalloids are sometimes called semimetals, but this practice is discouraged because 'semimetal' has a more common usage in physics referring to a specific electronic band structure; only arsenic and antimony are semimetals in that context, and they are commonly recognized as metalloids. Typical metalloids have a metallic appearance, may be brittle, and are only fair conductors of electricity. They can form alloys with metals, and many of their physical and chemical properties are intermediate between those of metallic and nonmetallic elements. Their compounds are used in alloys, biological agents, catalysts, flame retardants, glasses, optical storage and optoelectronics, pyrotechnics, semiconductors, and electronics. Classification of metalloids is judgment-based and varies by author. Some criteria include electronegativity values from 1.8 or 1.9 to 2.2, packing efficiency between 34% and 41%, or the Goldhammer–Herzfeld ratio around 0.85 to 1.1.

Reader's Guide

Metalloids hold significance as elements that defy simple classification into metals or nonmetals, illustrating the gradual nature of property changes across the periodic table. Their intermediate properties make them essential in modern technology, particularly as semiconductors and in optoelectronics, where their electrical conductivity can be finely tuned. The diagonal relationship they exhibit—where elements in different groups share similar properties—highlights an organizing principle of the periodic table, arising from competing horizontal and vertical trends in nuclear charge. The lack of a standard definition means that the number and identity of metalloids depend on the criteria used, with lists ranging from four to twelve elements. This ambiguity reflects the arbitrary nature of classification at the margins, as noted by Sharp. Despite this, the term persists because it captures a useful category for elements that are neither strongly metallic nor strongly nonmetallic. The dividing line between metals and nonmetals on some periodic tables helps locate metalloids, but alternative treatments may group them with metals, nonmetals, or treat them as a subcategory. Their legacy lies in challenging binary classification and enabling advances in electronics and materials science.

Did You Know?

• The word metalloid comes from Latin metallum ('metal') and Greek oeidḗs ('resembling in form or appearance').
• There is no standard definition of a metalloid and no complete agreement on which elements are metalloids.
• The six commonly recognized metalloids are boron, silicon, germanium, arsenic, antimony, and tellurium.
• Metalloids are sometimes called semimetals, but this practice is discouraged because 'semimetal' has a more common usage in physics.