Boron group

The boron group (Group 13 or IIIA) consists of six elements: boron (B), aluminum (Al), gallium (Ga), indium (In), thallium (Tl), and nihonium (Nh). All these elements lie in the p-block and share a valence electron configuration of ns²np¹ – that is, three electrons in their outer shell. Boron is a hard, black metalloid (semi-metal), while the others are silvery metals. The common oxidation state is +3, but the heavier members (especially thallium) often exhibit a +1 state due to the “inert pair” effect. In general, atomic size increases and ionization energy decreases down the group (making the heavier metals easier to ionize), and metallic character grows (boron is only a semiconductor, whereas Al–Tl are true metals).

• Electron configuration: All have three valence electrons (ns² np¹).
• Oxidation states: +3 is most common; +1 becomes important for heavier elements (Tl+, Nh+).
• Chemical trend: Atomic radius grows and ionization energy drops down the group, so Al–Tl are more chemically active metals than boron. Boron’s chemistry is nonmetallic, whereas Al, Ga, In, Tl are reactive metals.

Together, these trends mean boron behaves like a tough semiconductor, while aluminum is a light, corrosion-resistant metal, and gallium, indium, and thallium are progressively softer, denser metals. Nihonium is extremely unstable (only made atom-by-atom in labs) and its chemistry is still largely uncharted.

Boron (B, Z=5)

Main article: Periodic table/Boron group/Boron

Boron is a lustrous black metalloid (intermediate between metal and nonmetal) with atomic number 5. It is very hard (Mohs hardness ~9.3) but brittle. Boron occurs naturally not as a free element but in borate minerals (borax, kernite, etc.). Its most common oxidation state is +3, and in compounds boron often acts as a Lewis acid (electron-pair acceptor). Boron has only two stable isotopes (B-10 and B-11), and boron-10 is notable for its large neutron-absorption cross-section (used in neutron detectors and radiation shields).

Boron’s uses take advantage of its unique chemistry and strength. Small amounts of boron added to steel or aluminum alloys greatly increase hardness and strength. Boron compounds are key in everyday products: borosilicate glass (like Pyrex) contains boron, and borate salts (e.g. borax) are used in laundry detergents, fiberglass, and flame retardants. In electronics, boron is a standard dopant in silicon and germanium to create semiconductors (giving p-type conductivity). Boron is also vital in biology: trace boron (as boric acid/borate) is essential for healthy plant growth, although too much or too little causes problems. In excess, borates act as herbicides, while deficiency leads to stunted, deformed plants.

Interesting fact: In nature, elemental boron atoms form 12‑atom icosahedral clusters (see image). These cages give boron-rich solids unusual structures and explain the occasional term “icosagens” for Group 13. Boron also forms many boron-hydrogen compounds (boranes), some of which have exotic geometries and are studied for rocket fuel and medicine.

Aluminum (Al, Z=13)

Main article: Periodic table/Boron group/Aluminum

Aluminum is a lightweight, silvery metal with atomic number 13. It is by far the most abundant metal in Earth’s crust, though it never occurs as free metal in nature (it is always found combined in minerals like bauxite). Pure aluminum is soft and malleable, but it gains hardness and corrosion resistance when alloyed with small amounts of other metals (e.g. silicon or copper). Chemically, Al has a +3 oxidation state; it is quite reactive but its surface rapidly forms a thin oxide film (Al₂O₃) that prevents further corrosion, an effect known as anodizing. This oxide layer keeps aluminum “rust-free” and is why aluminum foil and cans last so long without rust.

Aluminum’s key uses stem from its low density (~2.7 g/cm³) and strength. It is widely used in cookware and packaging (foil, cans), in building and construction (siding, window frames, scaffolding) and especially in aerospace and automotive engineering (aircraft bodies, car parts). Aluminum also appears in electrical transmission lines (because it conducts electricity well and is much lighter than copper), and in consumer products from soda cans to smartphones. Important aluminum compounds include alumina (Al₂O₃), which is the basis of sapphires and rubies, and aluminum chloride (AlCl₃), a catalyst in many industrial organic reactions.

Interesting fact: For many decades after its discovery (1825), aluminum was a precious metal (more valuable than gold) because it was so hard to extract. Today the Hall-Héroult process (electrolysis of alumina) makes aluminum cheap and ubiquitous. Aluminum is also recyclable: melting down used aluminum saves ~95% of the energy needed to extract new metal.

Gallium (Ga, Z=31)

Main article: Periodic table/Boron group/Gallium

Gallium is a silvery metal (atomic number 31) with one very unusual property: it has a low melting point (about 30 °C) and will melt in your hand. Solid gallium is brittle, but its liquid metal wets glass and many surfaces. It expands on freezing (like water!), so it will shatter glass containers if frozen. Gallium’s electronic structure is [Ar]3d¹⁰4s²4p¹, with +3 as its common oxidation state. It was discovered in 1875 by Lecoq de Boisbaudran, confirming Dmitri Mendeleev’s “eka-aluminum” prediction for a missing element in the periodic table.

Gallium’s key use is in electronics. It forms important semiconductor compounds: gallium arsenide (GaAs) and gallium nitride (GaN) are used in LEDs and laser diodes. For example, GaAs LEDs emit infrared light (used in remote controls) and visible red/green light, and GaN LEDs produce bright blue and white light (used in modern LED bulbs and Blu-ray lasers). Gallium is also a component of galinstan (an alloy with indium and tin) that is liquid at room temperature and used as a non-toxic alternative to mercury in thermometers. Gallium’s broad liquid range (it stays liquid from near 30 °C up to ~2400 °C) also makes it a candidate coolant in some experimental nuclear reactors.

Interesting fact: You can make “galium crystals” by cooling liquid gallium, producing shiny, silvery crystalline pieces (see image). These seem solid at first but will melt if held. Gallium’s weird low-melting behavior and tendency to stick to metal surfaces were crucial clues in finding it (it was discovered from zinc ore through its spectral line and melting of equipment).

Indium (In, Z=49)

Main article: Periodic table/Boron group/Indium

Indium is a soft, silvery-white post-transition metal (atomic number 49). It has the electron configuration [Kr]4d¹⁰5s²5p¹ and commonly exhibits oxidation states +3 (and occasionally +1). Indium is very rare in Earth’s crust – about as scarce as silver – and is typically obtained as a by-product of zinc or lead ore processing. A neat property of indium metal is that it “wets” glass: molten indium will spread out and cling to glass or ceramics, which makes it useful for sealing things to glass. When a piece of indium metal is bent, it emits a distinctive “cry” (high-pitched sound), similar to tin’s “tin cry”.

Indium’s key uses are mostly in modern electronics. Its most famous application is in indium tin oxide (ITO), the transparent conductive coating on smartphone and tablet touchscreens and LCD displays. ITO conducts electricity while remaining clear, which lets touchscreens detect finger swipes. Indium compounds (like indium phosphide, InP) are also used in high-speed and optoelectronic devices (photodetectors, solar cells, LEDs). Metallic indium is used in low-melting fusible alloys (for example, in electrical fuses and safety devices) and as a bearing coating in aircraft engines to help protect against corrosion. Even the nuclear industry uses indium: indium foils detect neutrons in reactor cores.

Interesting fact: Indium makes up only a few parts per billion of the Earth’s crust, yet it became widely used in technology. The reason is its role in ITO and semiconductors. There is even concern about indium scarcity as display demand grows. Also, indium’s softness means you can scratch it with a fingernail – quite different from most metals.

Thallium (Tl, Z=81)

Main article: Periodic table/Boron group/Thallium

Thallium is a heavy, soft metal with atomic number 81. Its name comes from the Greek thallos (“green shoot”), after a bright green line in its spectrum which led Sir William Crookes to its discovery in 1861. In air, freshly cut thallium is lustrous silver, but it rapidly tarnishes to gray. It has oxidation states +1 and +3, and behaves chemically somewhat like the alkali metals (its Tl⁺ salts are water-soluble). Thallium is very rare in the Earth’s crust and is usually obtained from flue dusts when smelting zinc or lead ores.

Thallium is infamous for its toxicity – so toxic that it was once called the “poisoner’s poison.” Thallium salts (notably thallium sulfate) were widely used as rat poison and insecticide until the 1960s, when safer alternatives took over. Today thallium has very few common uses. Historically, it was added to special types of glass: small amounts of Tl₂O greatly increase the refractive index of glass, so thallium-containing lenses and prisms were made for infrared optics. Thallium isotopes (e.g. Tl-201) are used in medical imaging (cardiac stress tests). Some thallium compounds find niche uses in electronics (for example, Tl-doped detectors for radiation, and high-refractive lenses). However, almost all conventional uses have been phased out due to its hazard.

Interesting fact: Even a small exposure to thallium can cause serious harm. In fact, thallium’s deadly history includes many cases of poisoning, both accidental and deliberate. In chemistry, thallium is also noteworthy because it lies at the bottom of Group 13 and strongly exhibits the +1 oxidation state (due to the inert-pair effect). This makes it behave in some ways like the alkali metal cesium or the halogen astatine. (But that’s a topic for advanced chemistry discussions!)

Nihonium (Nh, Z=113)

Main article: Periodic table/Boron group/Nihonium

Nihonium is a superheavy synthetic element with atomic number 113. It was first created in 2003–2004 by bombarding americium (Am) with calcium (Ca) ions in particle accelerators, and the name (Nh) was approved in 2016 in honor of “Nihon,” Japan’s name in Japanese. All nihonium isotopes are extremely radioactive and have very short half-lives (the most stable known isotope, Nh-286, lasts only about 10 seconds). Nihonium is in Group 13, period 7, and is expected to be a post-transition metal (most like a heavier analog of thallium), but its chemistry is barely explored due to how little of it has been made.

Practically, nihonium has no uses outside scientific research. Only a few dozen atoms of nihonium have ever been detected, all in lab experiments. It’s so short-lived that no bulk samples exist, and we do not yet know its macroscopic properties (like melting point). Theoretical studies suggest nihonium will prefer the +1 oxidation state (like Tl). In current experiments, nihonium atoms have been observed forming simple compounds, but always under very controlled conditions. Thus nihonium’s “interesting fact” is simply that it marks the first element ever discovered in Asia, and it carries the legacy of being one of the superheavy members of the periodic table.

Summary Table of Group 13 Elements

Name	Symbol	Atomic Number	Key Use or Notable Property
Boron	B	5	Semiconductor dopant; used in borosilicate glass and to strengthen steel; essential micronutrient for plants.
Aluminum	Al	13	Lightweight structural metal; used in aircraft, vehicles, cans, foil, and building materials (oxide film makes it rust-proof).
Gallium	Ga	31	LED and laser semiconductor; used in GaAs and GaN devices (LEDs, solar cells, etc.); metal that melts in your hand (≈30 °C).
Indium	In	49	Transparent conductor; major component of ITO coatings for touchscreens and displays; used in LCDs and solders.
Thallium	Tl	81	Highly toxic heavy metal; historically in rodenticides (“rat poison”); limited modern uses in specialty glass and electronics.
Nihonium	Nh	113	Synthetic, radioactive; only produced atom-by-atom in labs; no applications (named after Japan’s “Nihon”).

Sources: Authoritative chemistry references and element profiles (see citations above). Each element entry in the table is based on the details given in the sections above.