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Boron group (group 13)
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
group 12 ←    → carbon group
IUPAC group number 13
Name by element boron group
Trivial name triels
CAS group number
(US, pattern A-B-A)
 IIIA
old IUPAC number
(Europe, pattern A-B)
 IIIB
↓ Period
2
Image: Boron chunks
Boron (B)
5 Metalloid
3
Image: Aluminium metal
Aluminium (Al)
13 Other metal
4
Image: Gallium crystals
Gallium (Ga)
31 Other metal
5
Image: Ductile indium wire
Indium (In)
49 Other metal
6
Image: Thallium pieces stored in a glass ampoule under argon atmosphere
Thallium (Tl)
81 Other metal
7 Nihonium (Nh)
113 other metal

Legend

primordial element
synthetic element

The boron group are the chemical elements in group 13 of the periodic table, consisting of boron (B), aluminium (Al), gallium (Ga), indium (In), thallium (Tl) and nihonium (Nh). This group lies in the p-block of the periodic table. The elements in the boron group are characterized by having three valence electrons.[1] These elements have also been referred to as the triels.[a]

Several group 13 elements have biological roles in the ecosystem. Boron is a trace element in humans and is essential for some plants. Lack of boron can lead to stunted plant growth, while an excess can also cause harm by inhibiting growth. Aluminium has neither a biological role nor significant toxicity and is considered safe. Indium and gallium can stimulate metabolism;[3] gallium is credited with the ability to bind itself to iron proteins. Thallium is highly toxic, interfering with the function of numerous vital enzymes, and has seen use as a pesticide.[4]

Characteristics

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Like other groups, the members of this family show patterns in electron configuration, especially in the outermost shells, resulting in trends in chemical behavior:

Z Element Electrons per shell
5 boron 2, 3
13 aluminium 2, 8, 3
31 gallium 2, 8, 18, 3
49 indium 2, 8, 18, 18, 3
81 thallium 2, 8, 18, 32, 18, 3
113 nihonium 2, 8, 18, 32, 32, 18, 3
(predicted)

The boron group is notable for trends in the electron configuration, as shown above, and in some of its elements' characteristics. An example of a trend in reactivity is boron's tendency to form reactive compounds with hydrogen.[5] However, boron differs from the other group members. It has the second highest hardness of all the elements, only exceeded by diamond.[6]: 145  Boron is considered a semi-metal while the others in the group are metals.[6]: 141  Boron's melting point at 2076 °C is much higher than the second highest in the group, aluminium, at 660 °C.[6]: 143 .

Chemical reactivity

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Hydrides

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Most of the elements in the boron group show increasing reactivity as the elements get heavier in atomic mass and higher in atomic number. Boron, the first element in the group, is generally unreactive with many elements except at high temperatures, although it is capable of forming many compounds with hydrogen, sometimes called boranes.[7] The simplest borane is diborane, or B2H6.[5] Another example is B10H14.

The next group-13 elements, aluminium and gallium, form fewer stable hydrides, although both AlH3 and GaH3 exist. Indium, the next element in the group, is not known to form many hydrides, except in complex compounds such as the phosphine complex H3InP(Cy)3 (Cy=cyclohexyl).[8] No stable compound of thallium and hydrogen has been synthesized in any laboratory.

Oxides

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All of the boron-group elements are known to form a trivalent oxide, with two atoms of the element bonded covalently with three atoms of oxygen. These elements show a trend of increasing pH (from acidic to basic).[14] Boron oxide (B2O3) is slightly acidic, aluminium and gallium oxide (Al2O3 and Ga2O3 respectively) are amphoteric, indium(III) oxide (In2O3) is nearly amphoteric, and thallium(III) oxide (Tl2O3) is a Lewis base because it dissolves in acids to form salts. Each of these compounds are stable, but thallium oxide decomposes at temperatures higher than 875 °C.

A powdered sample of boron trioxide (B2O3), one of the oxides of boron

Halides

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The elements in group 13 are also capable of forming stable compounds with the halogens, usually with the formula MX3 (where M is a boron-group element and X is a halogen.)[15] Fluorine, the first halogen, is able to form stable compounds with every element that has been tested (except neon and helium),[16] and the boron group is no exception. It is even hypothesized that nihonium could form a compound with fluorine, NhF3, before spontaneously decaying due to nihonium's radioactivity. Chlorine also forms stable compounds with all of the elements in the boron group, including thallium, and is hypothesized to react with nihonium. All of the elements will react with bromine under the right conditions, as with the other halogens but less vigorously than either chlorine or fluorine. Iodine will react with all natural elements in the periodic table except for the noble gases, and is notable for its explosive reaction with aluminium to form AlI3.[17] Astatine, the fifth halogen, has only formed a few compounds, due to its radioactivity and short half-life, and no reports of a compound with an At–Al, –Ga, –In, –Tl, or –Nh bond have been seen, although scientists think that it should form salts with metals.[18] Tennessine, the sixth and final member of group 17, may also form compounds with the elements in the boron group; however, because Tennessine is purely synthetic and thus must be created artificially, its chemistry has not been investigated, and any compounds would likely decay nearly instantly after formation due to its extreme radioactivity.

Physical properties

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It has been noticed that the elements in the boron group have similar physical properties, although most of boron's are exceptional. For example, all of the elements in the boron group, except for boron itself, are soft. Moreover, all of the other elements in group 13 are relatively reactive at moderate temperatures, while boron's reactivity only becomes comparable at very high temperatures. One characteristic that all do have in common is having three electrons in their valence shells. Boron, being a metalloid, is a thermal and electrical insulator at room temperature, but a good conductor of heat and electricity at high temperatures.[9] Unlike boron, the metals in the group are good conductors under normal conditions. This is in accordance with the long-standing generalization that all metals conduct heat and electricity better than most non-metals.[19]

Oxidation states

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The inert s-pair effect is significant in the group-13 elements, especially the heavier ones like thallium. This results in a variety of oxidation states. In the lighter elements, the +3 state is the most stable, but the +1 state becomes more prevalent with increasing atomic number, and is the most stable for thallium.[20] Boron is capable of forming compounds with lower oxidization states, of +1 or +2, and aluminium can do the same.[21] Gallium can form compounds with the oxidation states +1, +2 and +3. Indium is like gallium, but its +1 compounds are more stable than those of the lighter elements. The strength of the inert-pair effect is maximal in thallium, which is generally only stable in the oxidation state of +1, although the +3 state is seen in some compounds. Stable and monomeric gallium, indium and thallium radicals with a formal oxidation state of +2 have since been reported.[22] Nihonium may have +5 oxidation state.[23]

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There are several trends that can be observed in the properties of the boron group members. The boiling points of these elements drop from period to period, while densities tend to rise.

The 5 stable elements of the boron group
Element Boiling point Density (g/cm3)
Boron 4,000 °C 2.46
Aluminium 2,519 °C 2.7
Gallium 2,204 °C 5.904
Indium 2,072 °C 7.31
Thallium 1,473 °C 11.85

Nuclear

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With the exception of the synthetic nihonium, all of the elements of the boron group have stable isotopes. Because all their atomic numbers are odd, boron, gallium and thallium have only two stable isotopes, while aluminium and indium are monoisotopic, having only one, although most indium found in nature is the weakly radioactive 115In. 10B and 11B are both stable, as are 27Al, 69Ga and 71Ga, 113In, and 203Tl and 205Tl.[24] All of these isotopes are readily found in macroscopic quantities in nature. In theory, though, all isotopes with an atomic number greater than 66 are supposed to be unstable to alpha decay. Conversely, all elements with atomic numbers are less than or equal to 66 (except Tc, Pm, Sm and Eu) have at least one isotope that is theoretically energetically stable to all forms of decay (with the exception of proton decay, which has never been observed, and spontaneous fission, which is theoretically possible for elements with atomic numbers greater than 40).

Like all other elements, the elements of the boron group have radioactive isotopes, either found in trace quantities in nature or produced synthetically. The longest-lived of these unstable isotopes is the indium isotope 115In, with its extremely long half-life of 4.41 × 1014 y. This isotope makes up the vast majority of all naturally occurring indium despite its slight radioactivity. The shortest-lived is 7B, with a half-life of a mere 350±50 × 10−24 s, being the boron isotope with the fewest neutrons and a half-life long enough to measure. Some radioisotopes have important roles in scientific research; a few are used in the production of goods for commercial use or, more rarely, as a component of finished products.[25]

History

[edit]

The boron group has had many names over the years. According to former conventions it was Group IIIB in the European naming system and Group IIIA in the American. The group has also gained two collective names, "earth metals" and "triels". The latter name is derived from the Latin prefix tri- ("three") and refers to the three valence electrons that all of these elements, without exception, have in their valence shells.[1] The name "triels" was first suggested by International Union of Pure and Applied Chemistry (IUPAC) in 1970.[26]

Boron was known to the ancient Egyptians, but only in the mineral borax. The metalloid element was not known in its pure form until 1808, when Humphry Davy was able to extract it by the method of electrolysis. Davy devised an experiment in which he dissolved a boron-containing compound in water and sent an electric current through it, causing the elements of the compound to separate into their pure states. To produce larger quantities he shifted from electrolysis to reduction with sodium. Davy named the element boracium. At the same time two French chemists, Joseph Louis Gay-Lussac and Louis Jacques Thénard, used iron to reduce boric acid. The boron they produced was oxidized to boron oxide.[27][28]

Aluminium, like boron, was first known in minerals before it was finally extracted from alum, a common mineral in some areas of the world. Antoine Lavoisier and Humphry Davy had each separately tried to extract it. Although neither succeeded, Davy had given the metal its current name. It was only in 1825 that the Danish scientist Hans Christian Ørsted successfully prepared a rather impure form of the element. Many improvements followed, a significant advance being made just two years later by Friedrich Wöhler, whose slightly modified procedure still yielded an impure product. The first pure sample of aluminium is credited to Henri Etienne Sainte-Claire Deville, who substituted sodium for potassium in the procedure. At that time aluminium was considered precious, and it was displayed next to such metals as gold and silver.[28][29] The method used today, electrolysis of aluminium oxide dissolved in cryolite, was developed by Charles Martin Hall and Paul Héroult in the late 1880s.[28]

The mineral zinc blende, more commonly known as sphalerite, in which indium can occur.

Thallium, the heaviest stable element in the boron group, was discovered by William Crookes and Claude-Auguste Lamy in 1861. Unlike gallium and indium, thallium had not been predicted by Dmitri Mendeleev, having been discovered before Mendeleev invented the periodic table. As a result, no one was really looking for it until the 1850s when Crookes and Lamy were examining residues from sulfuric acid production. In the spectra they saw a completely new line, a streak of deep green, which Crookes named after the Greek word θαλλός (thallos), referring to a green shoot or twig. Lamy was able to produce larger amounts of the new metal and determined most of its chemical and physical properties.[30][31]

Indium is the fourth element of the boron group but was discovered before the third, gallium, and after the fifth, thallium. In 1863 Ferdinand Reich and his assistant, Hieronymous Theodor Richter, were looking in a sample of the mineral zinc blende, also known as sphalerite (ZnS), for the spectroscopic lines of the newly discovered element thallium. Reich heated the ore in a coil of platinum metal and observed the lines that appeared in a spectroscope. Instead of the green thallium lines that he expected, he saw a new line of deep indigo-blue. Concluding that it must come from a new element, they named it after the characteristic indigo color it had produced.[30][32]

Gallium minerals were not known before August 1875, when the element itself was discovered. It was one of the elements that the inventor of the periodic table, Dmitri Mendeleev, had predicted to exist six years earlier. While examining the spectroscopic lines in zinc blende the French chemist Paul Emile Lecoq de Boisbaudran found indications of a new element in the ore. In just three months he was able to produce a sample, which he purified by dissolving it in a potassium hydroxide (KOH) solution and sending an electric current through it. The next month he presented his findings to the French Academy of Sciences, naming the new element after the Greek name for Gaul, modern France.[33][34]

The last confirmed element in the boron group, nihonium, was not discovered but rather created or synthesized. The element's synthesis was first reported by the Dubna Joint Institute for Nuclear Research team in Russia and the Lawrence Livermore National Laboratory in the United States, though it was the Dubna team who successfully conducted the experiment in August 2003. Nihonium was discovered in the decay chain of moscovium, which produced a few precious atoms of nihonium. The results were published in January of the following year. Since then around 13 atoms have been synthesized and various isotopes characterized. However, their results did not meet the stringent criteria for being counted as a discovery, and it was the later RIKEN experiments of 2004 aimed at directly synthesizing nihonium that were acknowledged by IUPAC as the discovery.[35]

Etymology

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The name "boron" comes from the Arabic word for the mineral borax, (بورق, boraq) which was known before boron was ever extracted. The "-on" suffix is thought to have been taken from "carbon".[36] Aluminium was named by Humphry Davy in the early 1800s. It is derived from the Greek word alumen, meaning bitter salt, or the Latin alum, the mineral.[37] Gallium is derived from the Latin Gallia, referring to France, the place of its discovery.[38] Indium comes from the Latin word indicum, meaning indigo dye, and refers to the element's prominent indigo spectroscopic line.[39] Thallium, like indium, is named after the Greek word for the color of its spectroscopic line: thallos, meaning a green twig or shoot.[40][41] "Nihonium" is named after Japan (Nihon in Japanese), where it was discovered.

Occurrence and abundance

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Boron

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Boron, with its atomic number of 5, is a very light element. Almost never found free in nature, it is very low in abundance, composing only 0.001% (10 ppm)[42] of the Earth's crust. It is known to occur in over a hundred different minerals and ores, however: the main source is borax, but it is also found in colemanite, boracite, kernite, tusionite, berborite and fluoborite.[43] Major world miners and extractors of boron include Turkey, the United States, Argentina, China, Bolivia and Peru. Turkey is by far the most prominent of these, accounting for around 70% of all boron extraction in the world. The United States is second, most of its yield coming from the state of California.[44]

Aluminium

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Aluminium, in contrast to boron, is the most abundant metal in the Earth's crust, and the third most abundant element. It composes about 8.2% (82,000 ppm) of the Earth's crust, surpassed only by oxygen and silicon.[42] It is like boron, however, in that it is uncommon in nature as a free element. This is due to aluminium's tendency to attract oxygen atoms, forming several aluminium oxides. Aluminium is now known to occur in nearly as many minerals as boron, including garnets, turquoises and beryls, but the main source is the ore bauxite. The world's leading countries in the extraction of aluminium are Ghana, Suriname, Russia and Indonesia, followed by Australia, Guinea and Brazil.[45]

Gallium

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Gallium is a relatively rare element in the Earth's crust and is not found in as many minerals as its lighter homologues. Its abundance on the Earth is a mere 0.0018% (18 ppm).[42] Its production is very low compared to other elements, but has increased greatly over the years as extraction methods have improved. Gallium can be found as a trace in a variety of ores, including bauxite and sphalerite, and in such minerals as diaspore and germanite. Trace amounts have been found in coal as well.[46] The gallium content is greater in a few minerals, including gallite (CuGaS2), but these are too rare to be counted as major sources and make negligible contributions to the world's supply.

Indium

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Indium is another rare element in the boron group at only 0.000005% (0.05 ppm),.[42] Very few indium-containing minerals are known, all of them scarce: an example is indite. Indium is found in several zinc ores, but only in minute quantities; likewise some copper and lead ores contain traces. As is the case for most other elements found in ores and minerals, the indium extraction process has become more efficient in recent years, ultimately leading to larger yields. Canada is the world's leader in indium reserves, but both the United States and China have comparable amounts.[47]

Thallium

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A small bundle of fiberglass

Thallium is of intermediate abundance in the Earth's crust, estimated to be 0.00006% (0.6 ppm).[42] It is found on the ground in some rocks, in the soil and in clay. Many sulfide ores of iron, zinc and cobalt contain thallium. In minerals it is found in moderate quantities: some examples are crookesite (in which it was first discovered), lorandite, routhierite, bukovite, hutchinsonite and sabatierite. There are other minerals that contain small amounts of thallium, but they are very rare and do not serve as primary sources.

Nihonium

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Nihonium is an element that is never found in nature but has been created in a laboratory. It is therefore classified as a synthetic element with no stable isotopes.

Applications

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With the exception of synthetic nihonium, all the elements in the boron group have numerous uses and applications in the production and content of many items.

Boron

[edit]
Main article: Boron § Applications

Boron has found many industrial applications in recent decades, and new ones are still being found. A common application is in fiberglass.[48] There has been rapid expansion in the market for borosilicate glass; most notable among its special qualities is a much greater resistance to thermal expansion than regular glass. Another commercially expanding use of boron and its derivatives is in ceramics. Several boron compounds, especially the oxides, have unique and valuable properties that have led to their substitution for other materials that are less useful. Boron may be found in pots, vases, plates, and ceramic pan-handles for its insulating properties.

The compound borax is used in bleaches, for both clothes and teeth. The hardness of boron and some of its compounds give it a wide array of additional uses. A small part (5%) of the boron produced finds use in agriculture.[48]

Aluminium

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Main article: Aluminium § Applications

Aluminium is a metal with numerous familiar uses in everyday life. It is most often encountered in construction materials, in electrical devices, especially as the conductor in cables, and in tools and vessels for cooking and preserving food. Aluminium's lack of reactivity with food products makes it particularly useful for canning. Its high affinity for oxygen makes it a powerful reducing agent. Finely powdered pure aluminium oxidizes rapidly in air, generating a huge amount of heat in the process (burning at about 5500 °F or 3037 °C), leading to applications in welding and elsewhere that a large amount of heat is needed. Aluminium is a component of alloys used for making lightweight bodies for aircraft. Cars also sometimes incorporate aluminium in their framework and body, and there are similar applications in military equipment. Less common uses include components of decorations and some guitars. The element is also sees use in a diverse range of electronics.[49][50]

Gallium

[edit]
Main article: Gallium § Applications
Gallium is one of the chief components of blue LEDs

Gallium and its derivatives have only found applications in recent decades. Gallium arsenide has been used in semiconductors, in amplifiers, in solar cells (for example in satellites) and in tunnel diodes for FM transmitter circuits. Gallium alloys are used mostly for dental purposes. Gallium ammonium chloride is used for the leads in transistors.[51] A major application of gallium is in LED lighting. The pure element has been used as a dopant in semiconductors,[citation needed] and has additional uses in electronic devices with other elements. Gallium has the property of being able to 'wet' glass and porcelain, and thus can be used to make mirrors and other highly reflective objects. Gallium can be added to alloys of other metals to lower their melting points.

Indium

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Main article: Indium § Applications

Indium's uses can be divided into four categories: the largest part (70%) of the production is used for coatings, usually combined as indium tin oxide (ITO); a smaller portion (12%) goes into alloys and solders; a similar amount is used in electrical components and in semiconductors; and the final 6% goes to minor applications.[52] Among the items in which indium may be found are platings, bearings, display devices, heat reflectors, phosphors, and nuclear control rods. Indium tin oxide has found a wide range of applications, including glass coatings, solar panels, streetlights, electrophoretic displays (EPDs), electroluminescent displays (ELDs), plasma display panels (PDPs), electrochemic displays (ECs), field emission displays (FEDs), sodium lamps, windshield glass and cathode-ray tubes, making it the single most important indium compound.[53]

Thallium

[edit]
Main article: Thallium § Applications

Thallium is used in its elemental form more often than the other boron-group elements. Uncompounded thallium is used in low-melting glasses, photoelectric cells, switches, mercury alloys for low-range glass thermometers, and thallium salts. It can be found in lamps and electronics, and is also used in myocardial imaging. The possibility of using thallium in semiconductors has been researched, and it is a known catalyst in organic synthesis. Thallium hydroxide (TlOH) is used mainly in the production of other thallium compounds. Thallium sulfate (Tl2SO4) is an outstanding vermin-killer, and it is a principal component in some rat and mouse poisons. However, the United States and some European countries have banned the substance because of its high toxicity to humans. In other countries, though, the market for the substance is growing. Tl2SO4 is also used in optical systems.[54]

Biological role

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None of the group-13 elements has a major biological role in complex animals, but some are at least associated with a living being. As in other groups, the lighter elements usually have more biological roles than the heavier. The heaviest ones are toxic, as are the other elements in the same periods. Boron is essential in most plants, whose cells use it for such purposes as strengthening cell walls. It is found in humans, certainly as a essential trace element, but there is ongoing debate over its significance in human nutrition. Boron's chemistry does allow it to form complexes with such important molecules as carbohydrates, so it is plausible that it could be of greater use in the human body than previously thought. Boron has also been shown to be able to replace iron in some of its functions, particularly in the healing of wounds.[55] Aluminium has no known biological role in plants or animals, despite its widespread occurrence in nature.[56] Gallium is not essential for the human body, but its relation to iron(III) allows it to become bound to proteins that transport and store iron.[57] Gallium can also stimulate metabolism. Indium and its heavier homologues have no biological role, although indium salts in small doses, like gallium, can stimulate metabolism.[32]

Toxicity

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Each element of the boron group has a unique toxicity profile to plants and animals.

As an example of boron toxicity, it has been observed to harm barley in concentrations exceeding 20 mM.[58] The symptoms of boron toxicity are numerous in plants, complicating research: they include reduced cell division, decreased shoot and root growth, decreased production of leaf chlorophyll, inhibition of photosynthesis, lowering of stomata conductance,[59] reduced proton extrusion from roots,[60] and deposition of lignin and suberin.[61]

Aluminium does not present a prominent toxicity hazard in small quantities, but very large doses are slightly toxic. Gallium is not considered toxic, although it may have some minor effects. Indium is not toxic and can be handled with nearly the same precautions as gallium, but some of its compounds are slightly to moderately toxic.

Thallium, unlike gallium and indium, is extremely toxic, and has caused many poisoning deaths. Its most noticeable effect, apparent even from tiny doses, is hair loss all over the body, but it causes a wide range of other symptoms, disrupting and eventually halting the functions of many organs. The nearly colorless, odorless and tasteless nature of thallium compounds has led to their use by murderers. The incidence of thallium poisoning, intentional and accidental, increased when thallium (with its similarly toxic compound, thallium sulfate) was introduced to control rats and other pests. The use of thallium pesticides has therefore been prohibited since 1975 in many countries, including the USA.

Nihonium is a highly unstable element and decays by emitting alpha particles. Due to its strong radioactivity, it would definitely be extremely toxic, although significant quantities of nihonium (larger than a few atoms) have not yet been assembled.[62]

Notes

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Boron group

View on Grokipedia
from Grokipedia
The Boron group, also known as of the periodic table, consists of the elements (B, atomic number 5), aluminum (Al, 13), gallium (Ga, 31), indium (In, 49), (Tl, 81), and the synthetic (Nh, 113). These p-block elements are characterized by the general ns²np¹, where n is the principal , resulting in three valence electrons that typically lead to a +3 in their compounds. However, due to the , heavier elements like and increasingly favor the +1 . Boron stands out as a metalloid with semiconductor properties and poor metallic character, while aluminum, gallium, indium, and thallium are post-transition metals exhibiting increasing metallic luster, ductility, and conductivity down the group. Physical trends include rising atomic radii and decreasing ionization energies from boron to thallium, though nihonium's properties are largely predicted due to its short half-life of about 10 seconds for the most stable isotope, ^{286}Nh. Notable physical characteristics encompass aluminum's low density (2.70 g/cm³) and high ductility, gallium's unusually low melting point of 29.8°C, and thallium's softness and toxicity. In terms of occurrence, is found in minerals like , aluminum is the third most abundant element in (about 8.1% by mass, primarily as ), and , , and are rare, often obtained as byproducts of or aluminum processing. , discovered in 2004 by a Japanese team at , exists only in trace amounts from experiments and has no natural occurrence. Chemically, the group elements react with oxygen to form trioxides (e.g., Al₂O₃), with to produce trihalides, and with or acids to varying degrees, though boron's covalent nature makes it less reactive. The group's practical significance is dominated by aluminum, which is widely used in alloys, , and due to its resistance and nature, as the most produced (accounting for over 60% of that market as of 2023). compounds serve in glassmaking, detergents, and nuclear applications as neutron absorbers, while and are critical in semiconductors, LEDs, and solar cells. finds limited use in and despite its toxicity, and nihonium's study advances understanding of chemistry but has no current applications.

Properties

Physical properties

The boron group elements exhibit a range of physical properties that reflect their position in the p-block, transitioning from nonmetallic behavior in to increasingly metallic characteristics in the heavier members. These properties include variations in atomic size, phase behavior, density, electrical conductivity, and , influenced by the increasing number of electron shells and changing bonding nature down the group. Atomic radii increase down the group as additional electron shells are added, with boron's small covalent radius of 85 pm contrasting with thallium's larger metallic radius of 170 pm; intermediate values include aluminum at 143 pm, gallium at 135 pm, indium at 167 pm, and thallium at 170 pm (all metallic except boron). The melting and boiling points show an irregular trend, with boron having the highest melting point among the group at 2077 °C (for its amorphous form) due to its network covalent structure, followed by a sharp decrease to gallium's 29.8 °C—making it liquid at room temperature—before rising again for indium (156.6 °C) and thallium (304 °C). Boiling points follow a similar decreasing pattern from boron's 4000 °C to thallium's 1473 °C. Densities also increase down the group, starting low at 2.34 g/cm³ for boron and 2.70 g/cm³ for aluminum (contributing to its use in lightweight structures), rising to 5.91 g/cm³ for gallium, 7.31 g/cm³ for indium, and 11.85 g/cm³ for thallium. The following table summarizes these bulk properties:
Element (°C) (°C) (g/cm³)
207740002.34
660.325192.70
29.822295.91
156.620277.31
304147311.85
Data sourced from the Royal Society of Chemistry periodic table entries. Electrical conductivity increases down the group, with behaving as a or exhibiting low conductivity (resistivity around 10,000 μΩ·m at ), while aluminum and the heavier elements display metallic conductivity, with aluminum having particularly high values (approximately 3.77 × 10^7 S/m) suitable for electrical applications. Crystal structures vary significantly: forms complex allotropes based on icosahedral B_{12} units in rhombohedral arrangements, aluminum adopts a face-centered cubic lattice, gallium has an orthorhombic structure with unusual Ga-Ga dimer bonding, features a body-centered tetragonal form, and exhibits a hexagonal close-packed arrangement. The high of arises from strong covalent bonding within its extended icosahedral network, whereas gallium's anomalously low results from weak intermolecular forces in its orthorhombic , where delocalized electrons and Ga_2 dimers lead to reduced lattice stability. These physical trends align with the increasing metallic character observed down the group.

Chemical properties

The boron group elements exhibit a range of chemical behaviors influenced by their position in the periodic table, transitioning from non-metallic to metallic character down the group. Boron, as a non-metal, predominantly forms covalent, electron-deficient compounds due to its inability to easily achieve an octet through conventional two-center bonding, often relying on multicenter interactions. This leads to unique structures such as , which feature three-center two-electron bonds. Boron shares a with in the periodic table, manifested in similarities like the formation of acidic oxides and comparable reactivity in certain silicides and borides. Aluminum displays amphoteric behavior, reacting with both acids and bases to form salts. For instance, it dissolves in according to the equation: 2Al+6HCl→2AlCl3+3H22\mathrm{Al} + 6\mathrm{HCl} \rightarrow 2\mathrm{AlCl_3} + 3\mathrm{H_2} and in solution as: 2Al+2NaOH+6H2O→2Na[Al(OH)4]+3H22\mathrm{Al} + 2\mathrm{NaOH} + 6\mathrm{H_2O} \rightarrow 2\mathrm{Na[Al(OH)_4]} + 3\mathrm{H_2} (or simplified to formation). The heavier elements—gallium, , and —exhibit increasingly metallic properties, with their +3 compounds showing greater ionic character due to larger atomic sizes and lower charge densities compared to and aluminum./Descriptive_Chemistry/Elements_Organized_by_Period/Period_3_Elements/Acid-base_Behavior_of_the_Oxides) Hydrides of the group vary significantly in stability and structure. Boron forms volatile like (B₂H₆), characterized by electron-deficient three-center two-electron B-H-B bonds, which impart high reactivity and flammability. Aluminum hydride (AlH₃) exists as a polymeric solid with bridging , while the hydrides of , , and are unstable, often saline in nature, and decompose readily, reflecting the decreasing M-H bond strengths down the group. The oxides illustrate the group's reactivity trends, with acidity decreasing from top to bottom. Boron trioxide (B₂O₃) is a glassy, acidic solid that reacts with bases to form borates. Aluminum oxide (Al₂O₃) is amphoteric, dissolving in both acids and bases. The oxides of (Ga₂O₃), (In₂O₃), and (Tl₂O₃) are increasingly basic, while thallium(I) oxide (Tl₂O) is notably more stable than expected for a +3 oxide due to the preference for the +1 in thallium compounds./Descriptive_Chemistry/Elements_Organized_by_Block/3_d-Block_Elements1/Group_13:_The_Boron_Family/Z013_Chemistry) Halides provide insight into bonding preferences. Boron trihalides (BX₃) adopt trigonal planar geometries and act as strong Lewis acids, exemplified by BF₃, where the empty p-orbital on accepts electron pairs from donors; Lewis acidity increases from BF₃ to BI₃ due to reduced π-backbonding. Aluminum trihalides (AlX₃, X = Cl, Br, I) are dimeric in the gas phase, featuring halogen bridges to satisfy the . For the heavier elements, and trihalides retain some covalent character but trend toward ionic lattices, while thallium halides are predominantly in the +1 state (TlX), with TlX₃ often decomposing or existing as mixed-valent species. All elements form +3 halides, but does not produce simple aqua ions like [B(H₂O)₆]³⁺ due to its covalent nature and high charge density. diminishes down the group as metallic character increases, with and oxides showing weaker basic reactions toward acids compared to aluminum.

Oxidation states

The elements of the boron group possess a valence electron configuration of ns²np¹, where n increases down the group, leading to a common +3 oxidation state achieved by the loss of the three valence electrons./Descriptive_Chemistry/Elements_Organized_by_Block/2_p-Block_Elements/Group_13:_The_Boron_Family) Boron exhibits exclusively the +3 oxidation state, forming predominantly covalent compounds due to its high first three ionization energies, which make ionic bonding unfavorable./Descriptive_Chemistry/Elements_Organized_by_Block/2_p-Block_Elements/Group_13:_The_Boron_Family) Aluminum also predominantly displays the +3 oxidation state, often in ionic forms such as the hydrated salt AlCl₃·6H₂O, where the lower ionization energies relative to boron facilitate greater ionic character./Descriptive_Chemistry/Elements_Organized_by_Block/2_p-Block_Elements/Group_13:_The_Boron_Family) Gallium and indium primarily adopt the +3 oxidation state in their compounds, though the +1 state becomes accessible for these elements in certain subvalent species, such as indium(I) chloride (InCl). In thallium, the inert pair effect renders the +1 oxidation state more stable than +3, with the ns² electron pair becoming increasingly reluctant to participate in bonding due to poor shielding by d and f electrons; consequently, Tl³⁺ is unstable and the +3 state tends to disproportionate via the reaction 3Tl⁺ → 2Tl + Tl³⁺. This effect intensifies down the group, progressively stabilizing the +1 state relative to +3 as atomic size increases and effective nuclear charge on the s electrons rises./08:_Chemistry_of_the_Main_Group_Elements/8.06:Group_13(and_a_note_on_the_post-transition_metals)/8.6.02:_Heavier_Elements_of_Group_13_and_the_Inert_Pair_Effect) For the superheavy element nihonium, relativistic effects are predicted to further stabilize the 7s electron pair, favoring the +1 oxidation state over +3 and enhancing the inert pair influence beyond that observed in thallium. The periodic trends in the boron group (group 13) exhibit characteristic variations typical of p-block elements, with deviations arising from electron configurations and relativistic effects in heavier members. Atomic and ionic sizes generally increase down the group due to the addition of electron shells, but the elements display smaller radii compared to group 2 counterparts because of higher and poorer shielding by p electrons, which fail to effectively counter the increased proton pull on valence electrons./08%3A_Chemistry_of_the_Main_Group_Elements/8.06%3A_Group_13_(and_a_note_on_the_post-transition_metals)/8.6.01%3A_Properties_of_the_Group_13_Elements_and_Boron_Chemistry)/21%3A_The_p-Block_Elements/21.01%3A_The_Elements_of_Group_13) Atomic radii increase from boron (85 pm) to thallium (170 pm), reflecting the principal quantum number increase, though an anomaly occurs at gallium (135 pm), which is smaller than aluminum (143 pm) due to d-block contraction from poor shielding by intervening 3d electrons./21%3A_The_p-Block_Elements/21.01%3A_The_Elements_of_Group_13)/08%3A_Chemistry_of_the_Main_Group_Elements/8.06%3A_Group_13_(and_a_note_on_the_post-transition_metals)/8.6.01%3A_Properties_of_the_Group_13_Elements_and_Boron_Chemistry)
ElementAtomic radius (pm)
85
Aluminum (Al)143
135
Indium (In)167
170
Ionization energies decrease overall down the group, with the first ionization energy dropping from 801 kJ/mol for to 589 kJ/mol for thallium, facilitating easier removal in heavier elements. However, boron's second (2427 kJ/mol) and third (3660 kJ/mol) ionization energies are notably higher than those of aluminum (second: 1817 kJ/mol; third: 2745 kJ/mol), as they involve removing electrons from a stable half-filled p subshell and a smaller 2s orbital closer to the nucleus. An irregularity appears in gallium's first ionization energy (579 kJ/mol), slightly higher than aluminum's (578 kJ/mol), attributed to the increasing without proportional size increase./21%3A_The_p-Block_Elements/21.01%3A_The_Elements_of_Group_13)/08%3A_Chemistry_of_the_Main_Group_Elements/8.06%3A_Group_13_(and_a_note_on_the_post-transition_metals)/8.6.01%3A_Properties_of_the_Group_13_Elements_and_Boron_Chemistry)
ElementFirst IE (kJ/mol)Second IE (kJ/mol)Third IE (kJ/mol)
(B)80124273660
Aluminum (Al)57818172745
(Ga)57919792963
(In)55818212707
(Tl)58919712878
Pauling electronegativities decrease from 2.04 for to 1.62 for , signaling a transition from nonmetallic electron-attracting behavior in to more metallic, electron-sharing tendencies in heavier elements. Metallic character progressively strengthens down the group: boron behaves as a covalent semimetal with localized bonding, aluminum as a typical metal with delocalized electrons, and the heavier gallium, indium, and thallium as increasingly electropositive post-transition metals due to larger sizes and lower electronegativities./Descriptive_Chemistry/Elements_Organized_by_Block/2_p-Block_Elements/Group_13%3A_The_Boron_Family/1Group_13%3A_General_Properties_and_Reactions) Reactivity is lowest for boron owing to its high ionization energies and strong covalent bonds, rises sharply for aluminum with its favorable metallic properties, and then declines slightly for gallium, indium, and thallium as the inert pair effect stabilizes the ns² electrons, favoring +1 over +3 oxidation states and reducing willingness to lose all three valence electrons./08%3A_Chemistry_of_the_Main_Group_Elements/8.06%3A_Group_13_(and_a_note_on_the_post-transition_metals)/8.6.02%3A_Heavier_Elements_of_Group_13_and_the_Inert_Pair_Effect)/Descriptive_Chemistry/Elements_Organized_by_Block/2_p-Block_Elements/Group_13%3A_The_Boron_Family/1Group_13%3A_Chemical_Reactivity) Notable anomalies include a between boron-aluminum and beryllium-magnesium (group 2), driven by similar charge-to-radius ratios and electronegativities (Al 1.61, Be 1.57), leading to comparable behaviors like and complex formation. Additionally, , , and exhibit lower densities than anticipated from smooth group trends (e.g., gallium at 5.91 g/cm³ despite larger size than aluminum), resulting from structural irregularities and electronic effects like influencing packing efficiency./12%3A_Goup_2-_Alkaline_Earth_Metals/12.10%3A_Diagonal_Relationships_between_Li_and_Mg_and_between_Be_and_Al)/21%3A_The_p-Block_Elements/21.01%3A_The_Elements_of_Group_13)

Nuclear properties

The boron group elements exhibit varying nuclear stability, with lighter members possessing primarily stable isotopes and heavier ones showing increasing radioactivity. Boron, , , and occur naturally with stable or long-lived isotopes, while has one weakly radioactive isotope, and consists entirely of short-lived synthetic isotopes. None of the natural isotopes undergo , except for the extremely long-lived 115In^{115}\mathrm{In}, which decays via beta emission rather than fission. Boron has two isotopes: 10B^{10}\mathrm{B} with 19.9% abundance and 11B^{11}\mathrm{B} with 80.1%. The 10B^{10}\mathrm{B} isotope is notable for its high cross-section in reactions, such as 10B+n→7Li+4He^{10}\mathrm{B} + \mathrm{n} \to ^{7}\mathrm{Li} + ^{4}\mathrm{He}, which releases energetic particles and is utilized in nuclear applications like control rods and boron . Aluminium has a single stable isotope, 27Al^{27}\mathrm{Al}, which constitutes 100% of natural aluminium and shows no radioactivity.
ElementStable IsotopesNatural Abundances (%)
Gallium69Ga^{69}\mathrm{Ga}, 71Ga^{71}\mathrm{Ga}60.1, 39.9
Thallium203Tl^{203}\mathrm{Tl}, 205Tl^{205}\mathrm{Tl}29.5, 70.5
Gallium's two stable isotopes, 69Ga^{69}\mathrm{Ga} and 71Ga^{71}\mathrm{Ga}, occur in the listed abundances with no significant radioactivity in natural samples. Thallium similarly features two stable isotopes, 203Tl^{203}\mathrm{Tl} and 205Tl^{205}\mathrm{Tl}, both non-radioactive under normal conditions. Indium has one stable isotope, 113In^{113}\mathrm{In} at 4.1% abundance, and one radioactive isotope, 115In^{115}\mathrm{In} at 95.7% abundance, which undergoes beta decay with an extremely long half-life of 4.41×10144.41 \times 10^{14} years. This decay mode contributes negligibly to natural radioactivity levels. Nihonium, as a superheavy element, has no stable isotopes; all are synthetic and highly unstable, decaying primarily by alpha emission. The most stable known isotope, 286Nh^{286}\mathrm{Nh}, has a half-life of approximately 9.5 seconds. As increases across the group, nuclear stability decreases, reflected in the transition from fully stable isotopes to the rapid decay of nihonium's heavy nuclei.

The group, also known as of the periodic table, derives its name from , the first and lightest member of the group, reflecting its position in the third column (or in modern IUPAC numbering) of the p-block elements. The name originates from the Arabic word buraq (meaning "white") and the Persian burah, both referring to , the from which the element was isolated; it was coined in 1812 by as boracium by analogy to carbon, later shortened to boron. (or aluminum in ) comes from the Latin alumen, meaning "alum," a compound containing the element; proposed the name aluminum in 1808 after identifying the metal in alumina, though it was later adjusted to aluminium in 1812 to align with other metallic element names ending in -ium. Gallium is derived from the Latin Gallia, meaning "Gaul" or "France," honoring the discoverer's homeland; Paul-Émile Lecoq de Boisbaudran named it in 1875, with a possible secondary pun on gallus ("rooster" in Latin), alluding to his surname Lecoq ("the rooster"). Indium stems from the Latin indicium (or indicum), meaning "indigo," due to the prominent indigo-blue line observed in its atomic spectrum during discovery in 1863. Thallium originates from the Greek thallos, meaning "green shoot" or "young twig," named in 1861 by for the vivid green line in its spectrum. , the synthetic element 113, is named after Nihon (or Nippon), the Japanese word for "," recognizing the country where it was synthesized; the name was proposed by the team and officially approved by the International Union of Pure and Applied Chemistry in 2016.

Discovery of the elements

The element was first isolated in 1808 by English chemist by reducing with metal, producing an impure brown substance he named "boracium." In the same year, French chemists Joseph-Louis Gay-Lussac and Louis-Jacques Thénard independently obtained a similar impure form of by reducing with metal. These early isolations yielded only about 85% pure , with further purification achieved decades later using techniques like heating with sodium. Aluminium was initially identified in 1808 by , who analyzed and proposed the name "alumium" for the base in its compounds, though he did not isolate the metal. The pure metal was first produced in 1825 by Danish physicist and chemist , who reacted with a amalgam to yield small quantities of the element. Ørsted's method involved heating the reactants to drive the reduction, resulting in a metallic residue that confirmed the element's existence beyond its compounds. Thallium was discovered in 1861 by British chemist , who observed a vivid green while examining emissions from residues of production, specifically flue dust from the roasting of iron pyrites. This spectroscopic signature, absent in known elements, indicated a new substance; Crookes named it from the Greek word for "green twig." The metal was isolated shortly thereafter by of thallium chloride. Indium was discovered in 1863 by German physicist Ferdinand and metallurgist Hieronymus Theodor Richter during spectroscopic analysis of zinc ore samples from the mines. , who was color-blind, relied on Richter to observe the distinctive indigo-blue line in the spectrum, leading to the element's name. The pure metal was subsequently isolated by reducing indium chloride with sodium or . Gallium's existence was predicted in 1871 by Russian chemist as "eka-," an element below in his periodic table, with an expected atomic weight of about 68 and density of 6 g/cm³. French chemist Paul-Émile Lecoq de Boisbaudran isolated the element in 1875 from zinc blende ore using to detect its characteristic lines, followed by fractional precipitation and to obtain the pure metal, which closely matched Mendeleev's predictions. Nihonium, the synthetic completing the boron group, was first synthesized in by a team at in led by Kosuke Morita, through the fusion reaction of with zinc-70 ions accelerated in a linear accelerator, producing the nihonium-278. This achievement was confirmed in subsequent experiments in 2005 and 2012, leading to the International Union of Pure and Applied Chemistry (IUPAC) officially recognizing the discovery and granting to the RIKEN team in 2015.

Occurrence

Boron

Boron does not occur as the free element in nature and is always found in oxidized compounds called borates. Its abundance in is approximately 10 ppm (0.001% by weight), making it the 38th most abundant element. Boron is concentrated in the oceans and sediments due to the water-solubility of its compounds, with higher levels in arid regions. Primary minerals include (sodium tetraborate decahydrate, Na₂B₄O₇·10H₂O), kernite (Na₂B₄O₇·4H₂O), (Ca₂B₆O₁₁·5H₂O), (NaCaB₅O₆·8H₂O), and tincalconite. It also occurs as orthoboric acid (H₃BO₃) in some volcanic spring waters. Significant deposits are found in , the (e.g., ), , and .

Aluminium

Aluminium is the most abundant metallic element in Earth's crust, constituting about 8.1% by mass and ranking third overall after oxygen (46.6%) and silicon (27.7%). It occurs almost exclusively in oxidized forms, primarily as silicates in rocks and clays, but the principal economic source is bauxite ore, a mixture of hydrated aluminum oxides including gibbsite (Al(OH)₃), boehmite (γ-AlO(OH)), and diaspore (α-AlO(OH)). Bauxite forms through intense chemical weathering in tropical and subtropical regions. Other aluminous minerals include feldspars (e.g., orthoclase, KAlSi₃O₈), micas, and corundum (Al₂O₃). Aluminium is not found in its native metallic state due to its high reactivity. Major deposits are in Australia, Guinea, Brazil, Jamaica, and India.

Gallium

Gallium is a rare element with an estimated abundance of 16.9 ppm in , comparable to and lead, ranking it 34th in crustal abundance. It does not occur in concentrated deposits or as the but is dispersed in trace amounts, primarily substituting for aluminum and in minerals. The main sources are (aluminum ore), where it averages 50-100 ppm, and ( ore), with concentrations up to 3%. It also occurs in germanite (a copper ), , and some granitic rocks. Gallium is recovered as a byproduct during the processing of aluminum and ores. No significant primary deposits exist, and it is found globally wherever these host minerals occur, with notable production from , , and .

Indium

Indium is a very rare element, with a crustal abundance of approximately 0.05 ppm (50 ppb), making it the 68th most abundant and slightly more common than silver or mercury. It does not form distinct minerals but occurs in trace concentrations (typically 1-100 ppm) as an impurity in ores, particularly ( blende), where it substitutes for . Other sources include (lead ), ( ), and iron meteorites. is recovered almost entirely as a of ore processing, with minor contributions from tin and lead refining. Economic concentrations are rare, but deposits are associated with volcanogenic massive and sediment-hosted ores. Major sources are in , , and .

Thallium

Thallium has a crustal abundance of about 0.85 ppm (850 ppb), ranking it around 55th-60th in abundance, and is more concentrated in the upper at 0.55 mg/kg. It occurs primarily as a (up to 1%) in minerals, substituting for due to similar ionic radii, but is most economically sourced from iron, lead, , and ores. Key host minerals include (FeS₂), (PbS), (ZnS), and crookesite (a copper thallium ). Rare thallium minerals exist, such as lorándite (TlAsS₂) and hutchinsonite (TlPbAs₅S₉), but they are not commercially viable. Thallium is recovered as a byproduct of production from pyrites or /. It is widely dispersed, with elevated levels in coal and some volcanic rocks; notable deposits are in , , and .

Nihonium

Nihonium (element 113) is a synthetic with no natural occurrence on or in the , as it is not stable enough to form in . It is produced artificially in particle accelerators through reactions, such as bombarding americium-243 with ions. Only a few atoms have been synthesized since its discovery in 2004 by a team at in , with the most stable , nihonium-286, having a of about 19.6 seconds. Nihonium exists solely in laboratory settings for scientific study and decays rapidly via alpha emission.

Production

Boron

Boron is not found in elemental form in nature but is extracted from borate minerals such as (sodium tetraborate decahydrate) and kernite, primarily mined in , , and . The production process begins with mining these ores, followed by refining into through treatment with : Na₂B₄O₇·10H₂O + 2HCl → 4H₃BO₃ + 2NaCl + 5H₂O. Boric acid is then converted to other boron compounds or, for elemental boron, reduced using magnesium or electrolyzed from molten potassium fluoroborate (KBF₄). Global production of boron minerals was approximately 4.1 million metric tons in 2023, with the , , and as leading producers; elemental output is much smaller, around 100 metric tons annually, due to its specialized uses.

Aluminium

is produced from ore, the primary source containing 30–60% alumina (Al₂O₃), mined mainly in , , and . The process involves two main stages: the , where is digested with under high pressure and temperature to form , which is then precipitated as alumina hydrate and calcined to pure alumina; followed by the , an of molten alumina dissolved in (Na₃AlF₆) using carbon anodes to yield molten at the . Global primary aluminium production reached about 70 million metric tons in 2023, with accounting for over 60% of output; secondary production from adds around 30% more.

Gallium

is primarily obtained as a byproduct during the processing of for and ores, extracted from the acidic liquors or residues in alumina refineries and zinc smelters. The recovery involves solvent extraction or to isolate , followed by to produce high-purity metal. No dedicated gallium mines exist due to its low crustal abundance (about 19 ppm). World refined gallium production was estimated at 320 metric tons in 2023, with dominating at over 95%; the has no domestic production since 1987.

Indium

is recovered almost exclusively as a from , where it concentrates in the residues or sludges from and leaching processes; smaller amounts come from lead and . The metal is extracted via cementation with dust, followed by or for purification. Primary ores like contain trace indium (1–100 ppm). Global refined indium production was approximately 990 metric tons in 2023, led by (about 760 tons or 77%), followed by and .

Thallium

Thallium is produced solely as a byproduct from the smelting of , lead, and zinc sulfide ores, recovered from flue dusts, slags, or leaching residues through processes like sulfide precipitation or extraction, followed by . It is not mined directly due to its rarity and toxicity. Global production is minimal, estimated at less than 10 metric tons per year as of 2023, with primary producers being , , and ; the has had no domestic output since 1981.

Nihonium

, a synthetic , is produced in particle accelerators through reactions, specifically by bombarding a target with accelerated zinc-70 ions: ²⁰⁹Bi + ⁷⁰Zn → ²⁷⁸Nh + n (or other isotopes). The first synthesis occurred in 2004 at in , with only a few atoms created per experiment due to low cross-sections and rapid decay (half-lives of 10–20 seconds). No bulk production is possible. As of , fewer than 10 atoms have been produced in total across global facilities, solely for research into properties.

Applications

Boron

and its compounds find extensive use across various industries due to their unique chemical and physical properties. (sodium tetraborate) and are key compounds employed in detergents as cleaning agents and water softeners, enhancing the effectiveness of . These compounds are also integral to the production of heat-resistant , such as , where boron oxide improves thermal shock resistance and chemical durability, allowing the glass to withstand rapid temperature changes without cracking. In ceramics, borates act as fluxes to lower melting points and improve glaze adhesion, contributing to durable tiles and enamels. Additionally, in , boron compounds serve as micronutrients in fertilizers to address boron-deficient soils, promoting healthy plant growth in crops like nuts, fruits, and . Elemental has niche applications leveraging its nuclear and material properties. The ¹⁰B, with its high cross-section, is used in neutron absorbers for nuclear reactors, helping control fission reactions in control rods. Small additions of (typically 0.001–0.003%) to alloys enhance and high-temperature strength, improving mechanical properties in automotive and structural components. In the , serves as a p-type in wafers, enabling the fabrication of electronic devices like transistors and solar cells. In 2025, was designated a critical by the U.S. Department of the Interior, highlighting its importance in and amid concerns. Boranes and carboranes, classes of boron-hydrogen compounds, have specialized applications in and energy systems. Boranes have been explored as high-energy rocket fuels due to their exothermic properties, though limits widespread adoption. These compounds also show promise in for fuel cells, releasing on demand through or thermolysis. Carboranes function as cross-linkers in polymers, enhancing thermal stability and mechanical strength in high-performance composites for . The segment accounts for approximately 35% of global consumption as of 2025, with as a key application for fertilizers. Emerging applications highlight boron's versatility in . Boron nitride (BN), particularly in its hexagonal form, acts as a solid lubricant in high-temperature environments, reducing in engines and molds due to its graphite-like layered . Cubic boron nitride, with hardness comparable to , is used in cutting tools and abrasives for machining hard metals.

Aluminium

Aluminium's low of 2.7 g/cm³ contributes to its widespread use as a structural , enabling significant weight reductions in applications without compromising strength when alloyed. In the sector, aluminium-lithium (Al-Li) alloys are particularly valued for their high strength-to-weight ratio, forming 60–80% of the structural components in commercial aircraft by weight. These alloys, such as 2090 and newer variants, enhance and performance in airframes and fuselages. In transportation, aluminium alloys are extensively used in vehicles, including automotive bodies and components, where they account for up to 16% of a typical vehicle's weight by 2028 projections, improving energy efficiency. Globally, the transportation sector consumes approximately 30% of production, encompassing , automobiles, trucks, and railcars. Construction applications, representing about 20% of global aluminium use, include building facades, window frames, and roofing, where alloys provide durability and corrosion resistance. Overall, structural uses in transportation and comprise roughly 50% of total production. Packaging represents another major application, with used in beverage cans and foils due to its impermeability and formability. Globally, the sector accounts for about 15% of consumption, and aluminium cans achieve a rate of 75% as of 2023, far exceeding many other materials and enabling easy recovery through established collection systems. In electrical applications, aluminium's conductivity—approximately 61% that of —makes it the preferred material for overhead power lines, where its lighter weight reduces support structure costs despite slightly lower efficiency. This sector consumes about 10% of global , primarily in transmission and distribution wires. Other notable uses include aluminium surfaces to form a protective layer that enhances resistance, commonly applied in architectural and marine environments. , Al(OH)₃, serves as an active ingredient in antacids to neutralize acid and relieve . In , aluminium salts act as coagulants to aggregate impurities for , improving purification efficiency. Global primary aluminium production reached an estimated 70 million metric tons in 2023, supporting these diverse applications across sectors.

Gallium

Gallium and its compounds find extensive applications in , alloys, and due to their unique semiconductor properties and low melting points. In the , (GaAs) is widely used for light-emitting diodes (LEDs), solar cells, and circuits, benefiting from its high that enables efficient high-frequency performance. Similarly, (GaN) plays a critical role in blue LEDs and , where its wide bandgap supports high-efficiency light emission and robust operation in high-voltage devices. Gallium also serves as a in various semiconductors to enhance electrical conductivity and performance. Alloys of , particularly eutectic mixtures with such as (gallium-indium-tin), exhibit low melting points near or below , enabling their use in applications like , thermal management systems, and deformable mirrors. These room-temperature liquid alloys are valued for their conductivity and non-toxicity compared to mercury-based alternatives in thermometers and precision instruments. In , gallium-67 citrate is employed as a for tumor imaging in , where it accumulates in inflammatory and neoplastic tissues, aiding in the of lymphomas and other malignancies through detection. Global demand for high-purity stands at approximately 320 metric tons per year as of 2024 estimates, with over 95% directed toward applications including integrated circuits, , and telecommunications devices.

Indium

Indium finds its most significant application in the form of (ITO), a transparent conductive material used as coatings on substrates for liquid crystal displays (LCDs), touchscreens, and solar panels. This usage accounts for approximately 70% of global indium consumption, enabling the electrical conductivity and optical transparency essential for modern flat-panel electronics and photovoltaic devices. In addition to ITO, indium is alloyed with elements like to create low-melting-point materials employed in solders for electronic assemblies and fusible alloys for thermal fuses in devices. These alloys benefit from indium's and low melting temperature, facilitating reliable connections in precision and applications requiring controlled melting, such as . Indium phosphide (InP) serves as a key compound in the production of high-speed lasers and photodetectors for fiber optic communications, supporting telecommunications infrastructure with its direct bandgap properties that enable efficient light emission and detection. Beyond these, is utilized in thin-film transistors for advanced display technologies and in processes to coat bearings, enhancing resistance and reducing friction in and industrial components. Global production of refined reached approximately 990 metric tons in 2023, with demand predominantly driven by the sector, particularly displays and .

Thallium

Thallium's applications are highly restricted owing to its extreme toxicity, resulting in global consumption of less than 10 metric tons annually. This limited use contrasts with other boron group elements like , emphasizing thallium's niche roles in specialized fields where its unique physical properties outweigh the risks under strict controls. Primary applications include , , , and historical , with ongoing research into radiation-related technologies. In , thallium bromoiodide (KRS-5) is valued for its exceptional transmission across a wide spectrum, from approximately 600 nm to over 40 μm, making it ideal for prisms, windows, and lenses in and (ATR) setups. This material's high and chemical stability enable precise analysis in Fourier transform infrared (FTIR) instruments, though handling requires precautions due to 's hazards. Historically, sulfate (Tl₂SO₄) served as an effective starting in the 1930s, prized for its tastelessness and rapid action in baits for rats and . Its use peaked mid-20th century but was phased out and banned in many countries, including the by 1965, following numerous accidental human and animal poisonings that highlighted its dangers. Today, such applications are obsolete, replaced by safer alternatives. In electronics, thallium appears in trace amounts to enhance performance, particularly in doping selenium-based devices to improve sensitivity and electrical properties. It is also incorporated into photocells, where exposure to light alters its conductivity, enabling applications in light detection and measuring devices. Thallium's role here remains minor, often limited to specialized components like scintillation counters. For radiation applications, thallium-doped crystals are widely used in gamma detection equipment due to their high efficiency in converting gamma rays to visible light. In nuclear medicine, the radioisotope thallium-201 (²⁰¹Tl) is a key agent for myocardial perfusion imaging, where it is injected intravenously to evaluate coronary artery disease by assessing blood flow to the heart muscle at rest and under stress. This technique leverages ²⁰¹Tl's uptake in viable myocardial tissue proportional to perfusion, allowing single-photon emission computed tomography (SPECT) to detect ischemia with high sensitivity. Despite competition from technetium-99m agents, ²⁰¹Tl remains relevant for its first-pass extraction efficiency and ability to image myocardial viability.

Nihonium

Nihonium (Nh), element 113, has no known commercial or practical applications due to its extreme radioactivity and fleeting existence. It is produced solely in particle accelerators, where only a handful of atoms—typically fewer than one per day—have been synthesized in laboratory experiments. These minuscule quantities preclude any industrial, technological, or biological roles, as the element decays almost immediately after formation. Research on focuses on fundamental scientific inquiries into the behavior of elements, particularly probing the predicted "" where certain isotopes might exhibit longer half-lives due to nuclear shell effects. Studies also investigate relativistic effects on its electron structure, which are expected to stabilize unusual oxidation states such as +1 and +3, influencing its potential chemical bonding and reactivity in ways distinct from lighter elements. These experiments, conducted using techniques like , provide critical data for validating theoretical models of atomic and in the superheavy regime. While 's data extend the periodic table and deepen understanding of nuclear synthesis processes, its isotopes have half-lives on the order of 10 to 20 seconds, rendering any future practical uses implausible. The production of even a single atom demands vast resources, with accelerator beam time and experimental setups costing millions of dollars per attempt, far exceeding the value derived from such transient samples.

Biological and environmental aspects

Biological role

Among the elements in the boron group, only boron plays an established essential role in biological systems, primarily as a micronutrient in plants, while the others lack any confirmed beneficial functions and are generally incidental or inhibitory to organisms. Boron is an essential micronutrient for vascular plants, required in trace amounts typically ranging from 20 to 100 ppm in dry tissue weight depending on the species, where it supports key physiological processes such as pollen tube growth, seed development, and membrane integrity. Its primary function involves cross-linking rhamnogalacturonan II (RG-II) polysaccharides in cell walls through the formation of stable borate-diol ester complexes with apiose residues, which enhances cell wall porosity, elasticity, and structural integrity essential for plant growth and reproduction. In animals, including humans, boron has no confirmed essential role, though dietary supplementation has been associated with potential benefits in bone health, such as increased bone mineral density and modulation of hormone levels like estrogen and testosterone, based on observational and animal studies. Aluminum has no essential biological role in humans, animals, or most eukaryotic organisms and is generally considered non-bioactive due to its low and at neutral ; however, certain acidophilic in acidic environments, such as those in aluminum-contaminated soils, exhibit tolerance mechanisms that allow them to persist, potentially involving efflux pumps or strategies rather than active utilization. Gallium exhibits no natural biological role in organisms but can mimic iron (Fe³⁺) due to similar ionic radii and coordination chemistry, allowing it to interfere with iron-dependent metabolic pathways like siderophore-mediated uptake in ; this property is exploited in with gallium-67 or gallium-68 radiotracers for detecting and tumors, but it has no endogenous function. Indium has no known biological role and is not utilized by organisms, occurring only as a in some soils at concentrations below 0.1 ppm without evidence of uptake or metabolic incorporation in plants, animals, or microbes. Thallium possesses no biological role and acts primarily as a toxic analog to due to its similar ionic size (Tl⁺ ≈ K⁺), enabling it to substitute in potassium-binding sites on enzymes and ion channels, thereby disrupting cellular processes without any beneficial function. Nihonium, being a highly radioactive with a of seconds, has no relevance to biological systems due to its extreme scarcity and instability.

Toxicity

Boron exhibits low , with an oral LD50 of 2660 mg/kg in rats for boric acid equivalents. At higher doses exceeding 20 mg/day, it acts as a reproductive , impairing in animal models through mechanisms affecting sperm production and fetal development. is a mild and eye irritant upon direct contact, but is considered safe in trace amounts essential for growth and human nutrition, with no adverse effects observed below 13 mg/day in adults. Aluminum's toxicity is debated as a neurotoxin, with historical links to primarily from high-exposure cases in dialysis patients where contaminated dialysate led to and cognitive decline. It accumulates preferentially in bones, causing and in chronic overexposure scenarios. The oral LD50 exceeds 5000 mg/kg in rats for common salts like aluminum sulfate, indicating low acute lethality. Environmentally, acidification of soils and mobilizes aluminum, increasing and toxicity to aquatic organisms. Gallium demonstrates low overall toxicity, with oral LD50 values for exceeding 2000 mg/kg in rats, allowing its use in medical applications. However, (GaAs), a compound, is carcinogenic, classified as by IARC due to lung tumor induction in inhalation studies on . Intravenous injection of gallium compounds, such as or radiogallium for imaging, is generally safe at therapeutic doses, with minimal adverse effects reported in clinical settings for cancer diagnostics. Indium poses risks primarily through inhalation, causing lung fibrosis known as indium-tin pneumoconiosis (ITP) in workers exposed to indium-tin oxide (ITO) dust during manufacturing. This condition involves progressive with and alveolar proteinosis, linked to subchronic exposure levels as low as 0.1 mg/m³. The oral LD50 for indium chloride is greater than 2000 mg/kg in rats. Upon absorption, indium accumulates in the lungs and liver, exacerbating and inflammation in target organs. Thallium is highly toxic, with an oral LD50 of 15 mg/kg for thallium sulfate in rats, leading to severe systemic effects even at low doses. Acute poisoning manifests as alopecia, , and gastrointestinal distress, often progressing to multi-organ . Its toxicity stems from mimicking ions (K⁺) due to similar , disrupting cellular transport and inhibiting key enzymes like and kinase. Water-soluble salts, such as thallium and , are particularly dangerous, readily absorbed via ingestion or skin contact, with historical cases showing lethality from contaminated water sources. Nihonium, as a synthetic , exhibits extreme , decaying primarily via alpha emission with its longest-lived () having a of about 10 seconds. Potential arises from acute radiation poisoning upon hypothetical exposure, damaging tissues through high-energy alpha particles, though no documented human cases exist due to its laboratory synthesis in minute quantities. Elements like aluminum, , , and can bioaccumulate in the , with showing particular propensity to concentrate in and aquatic organisms, posing risks to higher trophic levels including humans. Aluminum bioaccumulates in under acidic conditions, while and from industrial effluents may enter sediments and transfer via ingestion, amplifying environmental exposure.

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