The metalloids or semimetals are a group of chemical elements with intermediate physical and chemical properties between metals and non-metals. Most chemical researchers accept the following chemical elements as metalloids: boron, silicon, arsenic, germanium, antimony, and tellurium (green in the image below).
However, a smaller group of researchers add polonium, astate (blue in color) and selenium (pink in color) to metalloids..
Even, based on some properties, they suggest that the chemical elements carbon and aluminum (yellow in color) should also be considered as metalloids..
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Metalloids are located on the periodic table on a downward diagonal between columns 13, 14, 15, 16, and 17, beginning with boron in the upper left and ending with astatine in the lower right..
Metals are to the left of metalloids and nonmetals to their right; therefore, they represent the border between both types of matter.
Metalloids form alloys with metals and react with non-metals, for example with oxygen, sulfur and halogens..
For the most part they are considered as electrical semiconductors, their conductance being temperature dependent. At low temperatures, the electrical conductance is low, so they act as electrical insulators, but as they heat up, their ability to conduct electricity increases..
Semiconductors are the basis of the development of the electronics industry, as well as that of computing and informatics. Likewise, the application that has been made of silicon has been very useful in this field.
Metalloids have different allotropic states (different crystalline forms); thus, for example, arsenic has black, yellow or gray crystals.
In nature, they are not usually found as pure chemical elements, but rather associated or forming aggregates in minerals together with lead, sulfur, iron, etc..
They appear as shiny solids. In this respect they resemble metals. They are brittle and not very elastic, so they cannot be stretched in the form of a wire, that is, they are not very ductile. In addition, its transformation into sheets is difficult, so the metalloids are not very malleable..
They are capable of conducting electricity and temperature, although to a lesser degree than metals. Within the metalloids there are chemical elements that, based on their band structures, are classified as semiconductors.
This group is made up of boron, silicon, germanium, and antimony. Arsenic and tellurium are classified as semi-metals.
Boron 2,076 ° C; Silicon 1,414 ° C; Germanium 938.25 ° C; Arsenic 817 ° C; Antimony 630.13 ° C; Tellurium 449.51º C and Polonium 254º C.
Boron 3,927 ° C; Silicon 3,265 ° C; Germanium 2,833 ° C; Arsenic 614º C; Antimony 1,587º C; Tellurium 988º C and Polonium 962º C.
Boron 2.34 g / cm3: Silicon 2.33 g / cm3; Germanium 5.323 g / cm3; Arsenic 5,727; Antimony 6,697 g / cm3; Tellurium 6.24 g / cm3 and Polonium 9.32 g / cm3.
They behave in a similar way to nonmetals, they form oxacids like SiOtwo and they have an amphoteric behavior. Metalloids can behave as an acid or a base depending on the pH of the medium..
-Arsenic is used in agriculture as an insecticide and herbicide. In addition, it is used to place it as a powder or in liquid solution on livestock to eliminate insects and parasites from the animal. Calcium arsenate is used to kill the cotton boll weevil.
-Arsenic is used as a wood preservative due to its toxicity to insects and fungi.
-Arsenic is used to treat Acute Promyelocytic Leukemia, a type of blood cancer. It is used in the preparation of Fowler's solution for use in the treatment of psoriasis. A radioactive isotope of arsenic (74As) is used in the localization of cancerous tumors present in the human body.
-Arsenic is part of Melarsoprol, a medicine used in the treatment of Human African Trypanosomiasis. Parasitic disease transmitted by the tsetse fly.
-Tellurium oxide has been used in the treatment of seborrheic dermatitis. Likewise, other tellurium compounds are used as antimicrobial agents..
-Boron, in the form of boric acid, is used as a mild antiseptic in the eyes, nose and throat.
-Tellurium is used in the production of blue, brown and red glasses. Metalloid can be electrolytically deposited on silver producing a blackish finish.
-Antimony is used to give glasses and enamels a yellow hue. Boron is used in the production of glass and ceramics. In particular, borosilicate glass is resistant to temperature changes, which is why it is used in laboratories in chemical reactions and distillations..
-At home, food can be baked using borosilicate glass, without breaking the utensils used..
-Silicon is the main base of the glass industry, involved in the manufacture of almost all glass objects.
-Germanium oxide is used in the manufacture of camera lenses and microscope lenses. In addition, it is used in the manufacture of the core of optical fibers for many applications..
-Arsenic forms alloys with lead, causing a decrease in its melting point. This causes a higher hardness in the alloy used in the production of shot.
-The addition of a quantity of tellurium between 0.1% and 0.6% of a leaded alloy increases its resistance to corrosion and to traction with an increase in flexibility. Tellurium is often added to cast iron to harden the surface layer of tempered parts..
-Antimony is used in alloys to produce bearings, accumulator plates, and printing material.
-Silicon is used in the production of alloys with higher resistance to acids. Such is the case of Duriron, which contains 14% silicon.
The alloy of silicon, iron and aluminum is used for the manufacture of parts of great hardness, which are used in the automotive industry.
-Arsenic forms alloys with platinum and copper to increase its resistance to corrosion. Also, arsenic is added to alpha-brass to increase the strength of the zinc. This type of brass is used in the manufacture of accessory materials for plumbing.
-Metalloids are used as semiconductors in the electronics and computer industry. In this sense, silicon is the leader in the semiconductor trade that forms the basis of modern electronics and computing. Silicon and its derivatives are used in computers, transitors, solar cells, and LCD screens..
-Tellurium is a semiconductor that has applications in electroptics and electronics.
-Germanium is a semiconductor metalloid that is used in conjunction with silicon in high-speed integrated circuits to improve their performance. Although germanium has somewhat displaced silicon in its semiconductor function, its use in the manufacture of miniaturized chips has been enhanced.
-Germanium is used in the manufacture of solar panels. Even exploring robots on the planet Mars contain germanium in their solar cells. In addition, germanium is used in the manufacture of radars..
Boron and its related compounds confer great resistance to the materials of which it is a part. This allows its use in the creation of spatial structures. Additionally, they are used in the production of golf clubs and fishing rods..
The protective action of boron carbide is used as control barriers in nuclear reactors, limiting the leakage of radioactive material. In addition, boron carbide is used in bulletproof vests and in the armor of war tanks..
Silicon dioxide and silica, in the form of clay or sand, are important components of bricks, concrete and cement, used in different forms of construction.
-Antimony sulfide is used in fireworks and flash lamps in cameras.
-Boron is part of neodymidium magnets.
-Silicone, a polymer derived from silicon, is used in the manufacture of oils and waxes, breast implants, contact lenses, explosives and in pyrotechnics.
-Germanium is used in the manufacture of fluorescent lamps and some LEDs. Additionally, germanium is used in electric guitars to produce a characteristic distortion tone..
-Germanium is used in thermal imaging application for military use and fire fighting.
-Antimony is used in the manufacture of matches and tracer and locator grenades, as well as in primers for cartridges.
-Sodium borate is used as a fire retardant in plastics and rubbers.
This group of chemical elements is made up of boron, silicon, antimony, tellurium, germanium, arsenic, polonium, and astate. However, the largest number of researchers in the field of chemistry exclude polonium and astate as metalloids..
Therefore, the most widely accepted group of metalloids would be made up of boron, silicon, antimony, tellurium, germanium and arsenic..
Polonium has been noted to be distinctively metallic, since its two allotropic forms are metallic conductors. On the other hand, astatine was classified in 2013 as a metal, although previously in 1950 it was designated as a halogen, a reactive nonmetal.
The boundary between the groups of elements considered as metals, metalloids, or non-metals is unclear. For this reason, some researchers, based on some property, suggest that this or that element should be considered as metalloid. It has been pointed out, for example, that carbon, aluminum or selenium should be classified as metalloids.
An attempt has been made to establish selection criteria that allow classifying a chemical element as metal, metalloids or nonmetal. Other selection criteria include ionization energy, electronegativity, and packing efficiency of the different chemical elements..
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