Science, Tech, Math › Science Semimetals or Metalloids Elements With Properties of Both Metals and Nonmetals Share Flipboard Email Print ALFRED PASIEKA / SCIENCE PHOTO LIBRARY / Getty Images Science Chemistry Periodic Table Basics Chemical Laws Molecules Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated July 17, 2019 Semimetals or metalloids are chemical elements that have properties of both metals and nonmetals. Metalloids are important semiconductors, often used in computers and other electronic devices. Boron (B): Atomic number 5Silicon (Si): Atomic number 14Germanium (Ge): Atomic number 32Arsenic (As): Atomic number 33Antimony (Sb): Atomic number 51Tellurium (Te): Atomic number 52Polonium (Po): Atomic number 84Tennessine (Ts): Atomic number 117 Although oganesson (atomic number 118) is in the last periodic column of elements, scientists do not believe it is a noble gas. Element 118 will most likely be identified as a metalloid once its properties have been confirmed. Key Takeaways: Semimetals or Metalloids Metalloids are chemical elements that display properties of both metals and nonmetals.On the periodic table, metalloids are found along a zig-zag line between boron and aluminum down to polonium and astatine.Usually, the semimetals or metalloids are listed as boron, silicon, germanium, arsenic, antimony, tellurium, and polonium. Some scientists also consider tennessine and oganesson to be metalloids.Metalloids are used to make semiconductors, ceramics, polymers, and batteries.Metalloids tend to be shiny, brittle solids that act as insulators at room temperature but as conductors when heated or combined with other elements. Semimetal or Metalloid Properties Semimetals or metalloids are found in a zig-zag line on the periodic table, separating the basic metals from the nonmetals. However, the defining characteristic of metalloids is not so much their position on the periodic table as the extremely small overlap between the bottom of the conduction band and top of the valence band. A band gap separates a filled valence band from an empty conduction band. Semimetals do not have a band gap. In general, metalloids have the physical properties of metals, but their chemical properties are closer to those of nonmetals: Semimetals tend to make excellent semiconductors, although most of the elements themselves are not technically semiconducting. Exceptions are silicon and germanium, which are true semiconductors, as they can conduct electricity under the right conditions.These elements have lower electrical and thermal conductivity than metals.Semimetals/metalloids have high lattice dielectric constants and high diamagnetic susceptibilities.Semimetals are typically malleable and ductile. One exception is silicon, which is brittle.Metalloids may either gain or lose electrons during chemical reactions. Oxidation numbers of elements in this group range from +3 to -2.As far as appearances go, metalloids range from dull to shiny.Metalloids are extremely important in electronics as semiconductors, although they are also used in optical fibers, alloys, glass, and enamels. Some are found in drugs, cleaners, and pesticides. The heavier elements tend to be toxic. Polonium, for example, is dangerous due to its toxicity and radioactivity. Distinction Between Semimetals and Metalloids Some texts use the terms semimetals and metalloids interchangeably, but more recently, the preferred term for the element group is "metalloids," so that "semimetals" may be applied to chemical compounds as well as elements that exhibit properties of both metals and nonmetals. An example of a semimetal compound is mercury telluride (HgTe). Some conductive polymers may also be considered semimetals. Other scientists consider arsenic, antimony, bismuth, the alpha allotrope of tin (α-tin), and the graphite allotrope of carbon to be semimetals. These elements are also known as the "classic semimetals." Other elements also behave like metalloids, so the usual grouping of elements isn't a hard-and-fast rule. For example, carbon, phosphorus, and selenium exhibit both metallic and nonmetallic character. To some extent, this depends on the form or allotrope of the element. An argument could even be made for calling hydrogen a metalloid; it normally acts as a nonmetallic gas but can form a metal under certain circumstances. Sources Addison, C.C, and D.B Sowerby. "Main Group Elements - Groups v and Vi." Butterworths, 1972.Edwards, Peter P., and M. J. Sienko. “On the Occurrence of Metallic Character in the Periodic Table of the Elements.” Journal of Chemical Education, vol. 60, no. 9, 1983, p. 691.Vernon, René E. “Which Elements Are Metalloids?” Journal of Chemical Education, vol. 90, no. 12, 2013, pp. 1703–1707.