Description

A metalloid is a chemical element with a majority of properties that fall between those of metals and those of nonmetals, or that are a mixture of the two. There is no universally accepted definition of a metalloid, and there is no consensus on which elements are metalloids. Despite its lack of precision, the word is still used in chemistry literature. Boron, silicon, germanium, arsenic, antimony, and tellurium are the six generally recognized metalloids. Carbon, aluminum, selenium, polonium and astatine are five of the least commonly classified elements. All eleven elements are found in a diagonal section of the p-block ranging from boron at the upper left to astatine at the lower right on a normal periodic table.

Metalloids have a metallic look, yet they are fragile and only good electrical conductors. Chemically, they mainly act like nonmetals. They can combine metals to make alloys. The majority of their other physical and chemical traits are intermediate. Metalloids are typically too brittle to be used in structural applications. Alloys, biological agents, catalysts, flame retardants, glasses, optical storage and optoelectronics, pyrotechnics, semiconductors, and electronics all employ them or their derivatives.

Metalloids are occasionally referred to as semimetals, which is incorrect because the term semimetal has a different meaning in physics than it does in chemistry. It refers to a specific type of electronic band structure of a substance in physics. Only arsenic and antimony are semimetals in this respect, and are frequently referred to as metalloids.
A metalloid is an element with a majority of qualities that are intermediate between, or a mixture of, those of metals and nonmetals, and so is difficult to categorize as either a metal or a nonmetal. This is a broad concept based on metalloid properties that have been repeatedly mentioned in the literature. The degree of difficulty in categorizing anything is an important factor. Most elements contain a combination of metallic and nonmetallic properties, and they can be classed based on which set of traits is more prominent. Metalloids are elements at or near the edges of the periodic table that lack a clear preponderance of either metallic or nonmetallic characteristics.

Metalloids include boron, silicon, germanium, arsenic, antimony, and tellurium, to name a few. One or more elements from selenium, polonium, or astatine are occasionally added to the list, depending on the author. Boron is sometimes omitted, either by itself or in combination with silicon. Tellurium is not always considered a metalloid.  It has been questioned whether antimony, polonium, and astatine should be classified as metalloids.

Metalloids are sometimes used to describe other elements. Hydrogen, beryllium, nitrogen, phosphorus, sulphur, zinc, gallium, tin, iodine, lead, bismuth, and radon are among these elements. Metalloid has also been applied to amphoteric elements with metallic luster and electrical conductivity, such as arsenic, antimony, vanadium, chromium, molybdenum, tungsten, tin, lead, and aluminum.

Periodic Table Territory

Metalloids are found on both sides of the metal-nonmetal dividing line. On some periodic tables, this can be found in various configurations. The elements on the bottom left of the line have more metallic behaviour, whereas the elements on the upper right have more nonmetallic behaviour.

The elements with the highest critical temperature for respective groups (Li, Be, Al, Ge, Sb, Po) are close below the line when displayed as a normal stair step. The metalloids' diagonal arrangement is an exception to the rule that elements with comparable characteristics tend to cluster together vertically. Other diagonal similarities between some elements and their lower right neighbors, such as lithium-magnesium, beryllium-aluminum, and boron-silicon, show a similar effect.

Due to dueling horizontal and vertical tendencies in the nuclear charge, this exception occurs. The nuclear charge, like the number of electrons, grows with atomic number through time. As nuclear charge rises, the increased pull on outer electrons often balances the screening effect of having more electrons. As a result of various anomalies, atoms become smaller, ionization energy rises, and the nature of the elements changes over time from highly metallic to weakly metallic to weakly nonmetallic to strongly nonmetallic. The effect of rising nuclear charge is often balanced by the effect of additional electrons being further away from the nucleus as one move along a major group. Atoms grow in size, ionization energy decreases, and metallic character rises.

Alternative Treatments

Although elements at the metal–nonmetal dividing line are not usually classed as metalloids, a binary classification can aid in the development of rules for defining metal, non-metal bond types. In such circumstances, rather than being worried about the marginal character of the items in question, the writers concerned focus on one or more attributes of interest to make their classification determinations. Their motivations may or may not be stated explicitly, and they may appear arbitrary at times. Metalloids can be classified as metals, nonmetals, or a subcategory of nonmetals.

Metalloid classification, according to some authors, "emphasizes that characteristics change gradually rather than suddenly as one proceeds across or down the periodic table."

Properties

Metalloids have the appearance of metals but behave more like nonmetals. They have the electronic band structure of a semimetal or semiconductor and are glossy, brittle solids with intermediate to good electrical conductivity. They are generally (weak) nonmetals with intermediate ionization energies and electronegativity values, as well as amphoteric or weakly acidic oxides. They can combine metals to make alloys. In nature, the majority of their other physical and chemical qualities are intermediate.

Catalysts

Boron trifluoride and trichloride are utilised as catalysts in organic synthesis and electronics, respectively; diborane is made from tribromide. In some transition metal catalysts, non-toxic boron ligands could substitute toxic phosphorus ligands. Organic processes use silica sulfuric acid. Despite worries about antimony contamination of food and beverages, germanium dioxide is occasionally used as a catalyst in the manufacturing of PET plastic for containers; cheaper antimony compounds, such as trioxide or triacetate, are more regularly utilized for the same reason. Selenous acid and tellurous acid, as well as arsenic trioxide, have been employed in the production of natural gas to increase carbon dioxide removal.