The Boron Group consists of the Group 13 (3A) elements of the Periodic Table: boron (B), aluminum (Al), gallium (Ga), indium (In), thallium (Tl), and nihonium (Nh) (formerly known as ununtrium – Uut, a synthetic element). These elements all have three valence electrons (general configuration ns2>np1). With the exception of the heavier ones, they commonly exhibit the oxidation state +3. The group is also called the aluminoids, since B and Al are the most abundant and significant representatives.
Group 13 Elements
- Boron (B) – a metalloid never found free in nature; forms hard covalent networks (crystalline B) and electron-deficient compounds (boranes, carboranes).
- Aluminum (Al) – a light metal, ductile, with excellent corrosion resistance due to passive Al₂O₃ film; highly abundant in the Earth’s crust (bauxite).
- Gallium (Ga) – low melting point (~29.8 °C), useful in semiconductors (GaAs, GaN) and optoelectronics.
- Indium (In) – applied in indium–tin oxide (ITO) for conductive coatings and displays; extracted as a byproduct of Zn refining.
- Thallium (Tl) – highly toxic; used in specialized optics, detection devices, and certain alloys.
- Nihonium (Nh) – a synthetic superheavy element, extremely unstable, with no practical applications.
Electronic configuration, oxidation states, and trends
With ns²np¹ valence configuration, Group 13 elements generally form compounds in the +3 state. However, in heavier members (Tl especially), the inert pair effect stabilizes the +1 state, making Tl(I) more common than Tl(III). For Ga and In, +3 is dominant, though +1 also occurs. Boron rarely forms B+; its chemistry is mainly covalent and electron-deficient, acting as a Lewis acid.
- Size and energy: Atomic radius increases from B → Tl, while ionization energy decreases. Ga is unexpectedly small due to d-block contraction (poor shielding by 3d electrons).
- Electronegativity: Boron is the most electronegative of the group, while Al, Ga, In, and Tl show increasing metallic character.
Lewis acidity, covalence, and coordination
Group 13 trihalides and trioxides (e.g., BF₃, BCl₃, AlCl₃) are classical Lewis acids, accepting electron pairs from donors (NH₃, ethers, halides). BF₃ is a strong electron pair acceptor due to its incomplete octet. AlCl₃ dimerizes in the gas phase (Al₂Cl₆) and is a major catalyst in Friedel–Crafts reactions.
Oxides, hydroxides, and acid–base behavior
- B₂O₃ and borates exhibit acidic behavior, forming boric acid (H₃BO₃) in water.
- Al₂O₃, Al(OH)₃, and analogous Ga/In hydroxides are amphoteric, reacting with both acids (yielding salts) and bases (yielding aluminates, gallates, etc.).
- Heavier oxides (In, Tl) tend toward basic behavior, consistent with their metallic nature.
Occurrence and extraction
- Boron: found in borate minerals like borax (Na₂B₄O₇·10H₂O) and kernite; used for glass, ceramics, and detergents.
- Aluminum: extracted from bauxite (hydrated oxides of Al) via the Bayer process (alumina) and Hall–Héroult electrolysis (metal).
- Gallium: present in trace amounts in bauxite and zinc ores; recovered as a byproduct of refining.
- Indium: obtained during zinc (sphalerite), lead, and copper processing.
- Thallium: found in sulfide ores of Cu/Pb/Zn; its production is limited due to toxicity.
Applications and technological relevance
- Glass and ceramics: Borosilicate glass (B₂O₃) with high thermal resistance; borates in glazes and insulation.
- Aluminum: structural and industrial applications (aerospace, packaging, construction, power transmission); Al₂O₃ used as abrasives and ceramics.
- Semiconductors: GaAs, GaN (LEDs, RF devices), InP (optoelectronics), ITO for transparent conductive films.
- Magnets and advanced materials: Nd₂Fe₁₄B permanent magnets (boron component), carboranes in medicinal and catalytic chemistry.
- Catalysis: AlCl₃ and boron compounds in organic synthesis and polymerization.
Safety and environmental considerations
- Thallium and some Ga/In compounds are highly toxic; handling requires PPE and proper disposal.
- Aluminum refining and boron mining generate industrial waste (red mud, high energy consumption), requiring environmental management.
Study trends (quick reference)
- Valence: ns²np¹ → typical oxidation state +3; +1 stable in Tl (and partially In/Ga).
- Lewis acids: BF₃, BCl₃, and AlCl₃ act as strong electron pair acceptors.
- Acid–base nature: B₂O₃ acidic → Al/Ga/In amphoteric → Tl oxides more basic.
- Structures: Boron favors covalent networks; metals (Al, Ga, In, Tl) show metallic bonding and complex formation.
FAQ – Frequently Asked Questions about the Boron Family
Which elements belong to the Boron Family?
B, Al, Ga, In, Tl, and Nh (nihonium, synthetic and unstable).
Why is the +1 state common in thallium?
Because of the inert pair effect: the ns² electrons in heavier elements are less available for bonding, stabilizing Tl(I) over Tl(III).
Is boron a metal?
No. Boron is a metalloid; its chemistry is mainly covalent and electron-deficient, acting as a Lewis acid (e.g., BF₃).
Why is aluminum resistant to corrosion?
Because it forms a protective oxide layer (Al₂O₃) that is thin, adherent, and prevents further oxidation.
What are the main applications of Ga, In, and Tl?
Ga and In are essential in semiconductors (GaAs, GaN, InP) and ITO films for displays. Tl has limited, controlled use due to toxicity.
Is “Ununtrium (Uut)” still a valid name?
No. The official name is nihonium (Nh), a synthetic element with a very short half-life and no applications.