Metalloids | Definition and Properties

Metalloids are a category of chemical elements in the Periodic Table, which are not Metals, nor Nonmetals. They are grouped by their properties in terms that they don’t show enough properties to be categorized either as Metals or Nonmetals. The Metalloids are a mixture of both types of elements and their properties or are near the margin of the two. Some Metalloids possess both metallic and nonmetallic properties, which makes them harder to classify. The official classification of Metalloids in the Periodic Table is as following: Boron (B), Silicon (Si), Arsenic (As), Tellurium (Te), Astatine (At). Metalloids can also be called semimetals, but this practice is strongly discouraged because of the confusion it can create with the Physics term “semimetal”.


Physical Characteristics of Metalloids

In terms of physical properties Metalloid elements usually have a metallic appearance. However, they are quite brittle. They are also fair electric conductors. Metalloids show a specific metallic shine and are solid in state. Their elasticity is brittle and their electrical conductivity various from intermediate to good.



Chemical Properties of Metalloids

While Metalloid elements may combine a mixture of nonmetal and metal properties in terms of chemical reactivity, they mostly show a nonmetallic chemical behavior. Their electronegativity and ionization energies fall between the ones of Metals and Nonmetals. The average ionization energy of Metalloid elements for kcal/mol is 199, but it may vary anywhere between 182 and 226. The average electronegativity of the Metalloid elements is 2.05 and it may vary from 1.90 (for Silicone) to 2.18 (for Arsenic). Their electronic band structures are either semimetal or semiconductor. Elements, going along a period in the Periodic Table, show an increase in their nuclear charge along the increase of their atomic numbers.


Bonding and reaction to other elements and compounds

Metalloid elements in the Periodic Table have a hybrid chemical reaction as a mixture of the way Nonmetals and Metals react with other elements and compounds. While their general chemical behavior is close to that of Nonmetals, they can show traces of metallic behavior. When exposed to Oxygen they can form amphoteric oxides or other weakly acidic oxides – a clear example of the hybrid reaction between metallic and nonmetallic behavior. When Metalloid elements are mixed with other Metals, they form various alloys.

Uses and applications of Metalloids

Due to the fact that they are quite brittle, Metalloid elements cannot have any structural use when they are in their pure form. However, their compounds and the alloys they form have a large application in many industries, including metallurgy, medicine, food industry, glass manufacturing, electronics, pyrotechnics, optoelectronics, gardening and so on.

The six basic Metalloid elements in the Periodic Table show great medicinal and dietary properties, regardless of the fact that they can be toxic. Antimony, Arsenic, Boron and Silicon find application in the medicine, while Boron is also used in gardening for herbicides and insecticides. Metalloids can be used as biological agents for toxicological, medicinal and nutritional purposes, in optical storage media, as semiconductors, as oxide glasses, and catalysts, as flame retardants, and so on.



Metalloids on Earth

Metalloid elements vary in abundance on Earth. Not only are some of them rare, but they are also toxic. The most abundant Metalloid of the Periodic Table is Silicone. Not only that, but Silicon is also the second element in the most abundant elements on our planet, being preceded only by Oxygen. Boron and Arsenic are second and third in the table of most abundant Metalloids on Earth. Tellurium is the rarest Metalloid element on our planet and its crust. In fact, it’s just as rare as Platinum is.