The properties of semimetals or metalloids

Metalloids or semimetals are elements with properties intermediate between metals and nonmetals. As a group, the metalloids have at least one shiny, metallic-looking allotrope. Solids are brittle, with non-metallic chemical properties. Although metalloids are not good electrical or thermal conductors, they are excellent semiconductors and form amphoteric oxides .

Metalloids on the periodic table

There are 70 metals or metalloids, and they are among the nonmetals on the periodic table of elements. Elements in this category have properties intermediate between nonmetals and metals. The exact elements that are considered metalloids are debated, as different classification systems consider different elements to be metalloids.

However, the following elements are generally considered to be metalloids or semimetals: boron (5), silicon (14), germanium (32), arsenic (33), antimony (51), tellurium (52), and astatine (85).

structure of metalloids

Metalloids have a crystalline structure that results from a covalent bond. Elemental silicon, antimony, arsenic, germanium, and tellurium have a high luster, making them look like metals. When crystallized, germanium and silicon have a diamond-like structure. The atoms in the crystal have covalent bonds that anchor them to four neighboring atoms at the corners of a tetrahedron. Single crystals of germanium and silicon are made up of huge three-dimensional molecules.

Arsenic has several different allotropes, the most stable being that with a layered structure of sheets of arsenic atoms. The arsenic atoms are bonded to three other atoms that surround them. Both antimony and arsenic have graphite-like structures arranged in a lattice. Tellurium contains crystals with endless chains of spiral-shaped tellurium atoms.

Boron forms an icosahedron with boron atoms at each corner, and the crystal structure is transparent. The most common arrangement of atoms is one in which they are extremely close to each other, with boro-boron bonds having a length of about 176 µm. There are also other forms of icosahedrons, which have a different arrangement of boron atoms.

The silicon metalloid readily forms compounds with oxygen, creating bonds in the Si-O-Si format. These bonds are extremely important in the formation of minerals, just like the carbon bonds that are so important in the formation of organic compounds in plants and animals.

Physical and chemical properties of metalloids

Physical properties are characteristics that can be documented or observed without altering the substance of the element, without changing the group of molecules in substances. On the other hand, physical properties include aspects such as freezing point and density. The physical properties of metalloids are as follows:

• Metalloids have a solid state of matter.
• In general, metalloids have a metallic luster.
• Metalloids have little elasticity, they are very brittle.
• The intermediate weights are semiconductor elements and allow medium heat transmission.

Chemical properties are those that define how a substance interacts or reacts with other substances or transforms one substance into another. Chemical reactions are the only moment in which the chemical properties of an element can be quantified. On the other hand, chemical reactions include phenomena such as precipitation, combustion, fogging, explosion, etc. The chemical properties of metalloids are as follows:

• Metalloids readily form gases when oxidized.
• To create alloys, metalloids can be combined with metals.
• Metalloids have different metallic and nonmetallic allotropes .
• When metalloids melt, some contract.
• Metalloids can react with halogens to form compounds.

Common uses of metalloids

Metalloids are more brittle and have no structural utility in their pure form. These compounds can be used as:

1. Alloys . Early in the history of intermetallic compounds, the British metallurgist Cecil Desch observed that certain non-metallic elements are capable of forming purely metallic compounds with metals, so these specific elements can enter into the composition of alloys.
2. Biological agents. In general, the six elements are recognized as metalloids with dietary, medicinal, or toxic properties. Antimony and arsenic compounds are especially toxic; silicon, boron and possibly arsenic are the main trace elements. Silicon, boron, antimony, and arsenic have medical applications. At the same time, tellurium and germanium are believed to have potential.
3. Catalysts . Boron trichloride and trifluoride can be used as catalysts in electronics and organic synthesis; the tribromide can be used in the manufacture of diborane. Furthermore, non-toxic boron ligands could replace toxic phosphorus ligands in some transition metal catalysts.

Interesting facts about some metalloids

• The most abundant metalloid in the Earth’s crust is silicon, which is the second most abundant element overall (oxygen is first).
• The least abundant natural metalloid is tellurium.
• Metalloids are valuable in the electronics industry, for example silicon is used to make the chips found in phones and computers.
• Arsenic and polonium are highly toxic metalloids.
• Antimony and tellurium are used primarily in metal alloys to add desirable properties.

Fountain

Lopez, M. (2018). Metalloids . Monograph.