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Metalloid

physical science Maturity 9-11 Next article →

A metalloid is a chemical element that occupies a middle ground between metals and nonmetals. The term originates from the Latin *metallum*, meaning metal, and the Greek *oeidḗs*, meaning resembling in form or appearance.

Boron R105
Boron R105

Because these elements possess a mixture of properties, they are often difficult to classify. Most elements in the periodic table show a clear preference for being either metallic or nonmetallic. Metalloids are unique because they lack a sufficiently clear preponderance of one set of traits over the other. This makes their classification somewhat arbitrary and subject to debate among scientists.

To understand how metalloids work, we must look at their physical and chemical behaviors. They often exhibit a metallic luster, which is a shiny appearance. However, unlike many metals, they are frequently brittle and may break easily under pressure.

Arsen 1a
Arsen 1a

A defining feature is their electrical conductivity. While metals are excellent conductors, metalloids are often fair or poor conductors. Many act as semiconductors, meaning they can control the flow of electricity.

They can also form alloys, which are mixtures of different elements, by combining with metals. This ability to bridge the gap between different types of matter is central to their utility.

There is no single, universally accepted list of metalloids. However, six elements are commonly recognized: boron, silicon, germanium, arsenic, antimony, and tellurium.

Polycrystalline-germanium
Polycrystalline-germanium

On a standard periodic table, these elements form a diagonal region in the p-block. This path extends from boron in the upper left to astatine in the lower right.

Tellurium2
Tellurium2

Some scientists include additional elements like carbon, aluminium, selenium, polonium, and astatine. Others have suggested much longer lists, including elements like bismuth or even hydrogen. Because the inclusion of certain elements depends on the specific criteria used, the exact number of metalloids can vary widely in scientific literature.

Historically, the meaning of the word "metalloid" has shifted significantly. Originally, the term was used to refer to nonmetals. The modern definition, which describes a category of elements with hybrid or intermediate properties, became widespread between 1940 and 1960.

Antimony-4
Antimony-4

Some researchers previously used the term "semimetals" to describe them. Today, this practice is discouraged because "semimetal" has a specific meaning in physics regarding electronic band structures. In that specialized context, only arsenic and antimony are considered semimetals.

Scientists use several quantitative measures to identify these elements. One common method is measuring electronegativity, which is an atom's ability to attract electrons. Metalloids typically have electronegativity values between 1.8 or 1.9 and 2.2.

Selenium black (cropped)
Selenium black (cropped)

Another measure is ionization energy, the energy required to remove an electron. Commonly recognized metalloids have average ionization energies around 837 kJ/mol. Scientists also look at packing efficiency, which is the fraction of volume in a crystal structure occupied by atoms. Metalloids generally have packing efficiencies between 34% and 41%.

Metalloids are essential to modern technology due to their unique electronic properties. They are used in the production of semiconductors, which are the foundation of almost all modern electronics.

Blue Light
Blue Light

They are also vital for creating optical storage devices and optoelectronics. In communications, they play a role in the technology used for optical fibers.

Fibreoptic4
Fibreoptic4

Beyond high-tech gadgets, metalloids and their compounds are used in flame retardants, pyrotechnics, and special types of glass. They even serve as biological agents and catalysts in various chemical processes.

The placement of metalloids on the periodic table reveals interesting trends in atomic physics. As you move across a period from left to right, the increasing nuclear charge makes atoms smaller and increases ionization energy. This causes a gradual shift from metallic to nonmetallic character. Conversely, moving down a group increases the distance between the nucleus and outer electrons, which increases metallic character. The diagonal positioning of metalloids is an exception to the rule that similar elements usually appear in vertical groups. This unique arrangement occurs because horizontal and vertical trends in nuclear charge compete with one another.

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🖼️ Images & Media (14)
File:Copper germanium.jpg
Copper germanium.jpg
File:Arsenic trioxide.jpg
Arsenic trioxide.jpg
File:Fibreoptic4.jpg
Fibreoptic4.jpg
File:Blue Light.JPG
Blue Light.JPG
File:Boron R105.jpg
Boron R105.jpg
File:Polycrystalline-germanium.jpg
Polycrystalline-germanium.jpg
File:Arsen 1a.jpg
Arsen 1a.jpg
File:Antimony-4.jpg
Antimony-4.jpg
File:Tellurium2.jpg
Tellurium2.jpg
File:Graphite2.jpg
Graphite2.jpg
File:Aluminium-4.jpg
Aluminium-4.jpg
File:Selenium black (cropped).jpg
Selenium black (cropped).jpg

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