Group 13 Elements

The Boron family, also known as Group 13 on the Periodic table, is situated in the p-block and includes the elements boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (Tl). These elements share some common characteristics and trends as you move down the group. In this article we will learn group 13 elements properties and Important compounds of Group 13.

1.0Important Characteristics of group 13 elements

Occurrence of Group 13 Elements

• Boron is not found free in nature but in compounds such as orthoboric acid, (H₃BO₃), Borax, (Na₂B₄O₇·10H₂O), and Kernite, (Na₂B₄O₇·4H₂O). There are two isotopic forms of boron ¹⁰B (19%) and ¹¹B (81%).
• Aluminum is the most abundant metal in the Earth's crust. Bauxite, (Al₂O₃.2H₂O) and cryolite, (Na₃AlF₆) are the important minerals of aluminium.
• Gallium, Indium, and Thallium are much less abundant, found in trace amounts in various minerals and ores.

Electronic Configuration of Group-13

The outer electronic configuration of Group 13 elements is (ns² np¹). Boron and aluminum have a noble gas core, while gallium and indium add 10 d-electrons, and thallium includes 14 f-electrons and 10 d-electrons. This complexity in electronic structure influences their chemical properties and behavior.

2.0Physical Properties of Group 13

1. State at Room Temperature:

2. Melting and Boiling Points:

The boiling points of the Group 13 elements show a trend generally decreasing down the group.

• Boiling Point order will be: B > Al > Ga > In > Tl  
• In Group 13, the melting points of the elements vary significantly, affected by their electronic structures and bonding.
• Note- Gallium (Ga): Lowest at about 30°C, exceptionally low for a metal, due to its unusual electronic configuration that weakens metallic bonds.
• Melting Point order will be: B > Al > Tl > In > Ga

3. Atomic radii of Group-13

• Atomic radii typically increase as you move down Group 13 because each successive element adds an extra electron shell. 
• However, there's an anomaly: the atomic radius of gallium is smaller than that of aluminum. This unexpected trend can be explained by differences in their electronic configurations. Gallium has an additional 10 d-electrons which provide poor shielding of the outer electrons from the nucleus. As a result, despite having more electron shells, gallium (135 pm) has a smaller atomic radius compared to aluminum (143 pm). 
• The order of atomic radii in Group 13 is B < Ga < Al < In < Tl, which reflects this deviation.

4. Electronegativity

• In Group 13, electronegativity decreases from boron to aluminum due to increasing atomic size, which reduces the atoms' ability to attract electrons. 
• However, despite further increases in size, electronegativity slightly increases from aluminum onwards. This rise is due to the higher nuclear charge, which somewhat offsets the effects of poor electron shielding by the inner shells, thus enhancing the pull on valence electrons.

3.0Chemical Properties of group 13 elements

1. Oxidation States and Inert Pair Effect:

oxidation number of group 13 elements

• Boron (B) typically exhibits a +3 oxidation state. Due to its small size and high ionization energies, boron tends to form covalent bonds.
• Aluminum (Al) predominantly exhibits the +3 oxidation state and forms ionic compounds like AlCl₃ and Al₂O₃.
• Gallium (Ga), Indium (In), and Thallium (Tl) also show a +3 oxidation state in most compounds, but thallium additionally exhibits a +1 oxidation state due to the inert pair effect, which makes Tl+ more stable than Tl³⁺.
• The "inert pair effect" is an observed phenomenon in some heavy elements of the p-block, particularly in Group 13, where the two s-electrons in the outermost shell are less chemically reactive. This leads to the stabilization of lower oxidation states. 
• For example, while elements like thallium are expected to exhibit a +3 oxidation state by losing three valence electrons, they often favor a +1 state because the s-electrons are "inert" or less available for bonding due to increased relativistic effects and greater electron shielding. This effect becomes more pronounced as you move down the group, from aluminum to thallium.

2. Reactivity with Water

• Boron: Does not react with water under normal conditions.
• Aluminum: Reacts with water only when its protective oxide layer is damaged or treated chemically.
• Gallium, Indium, Thallium: These metals react with water more readily at higher temperatures, forming their respective hydroxides and hydrogen gas.

3. Reactivity with Acids and Bases

• Boron: Resistant to attack by boiling HF and HCl but dissolves in molten alkalis.
• Aluminum: Reacts with both acids and bases, demonstrating amphoteric behavior. It can react with HCl to produce AlCl₃ and H₂, or with NaOH to produce sodium aluminate and hydrogen.

                2Al(s)  + 6HCl(aq)   →   2Al³⁺ (aq)   +   6Cl^⊖(aq)  + 3H₂(g)

                2Al (s)  +  2NaOH(aq)  +  6H₂O(l)   →   2Na^⊕[Al(OH)₄]^⊖ (aq) + 3H₂(g)

• Gallium, Indium, Thallium: Similar to aluminum, these are amphoteric. Thallium, especially in the +1 state, reacts with acids to form thallium(I) salts.

4.0Important Compounds of Group 13 Elements

Boron Compounds

1. Boric Acid (H₃BO₃)

• Properties: White, crystalline solid; soluble in water; has mild antiseptic, antifungal, and antiviral properties.
• Synthesis: Most commonly produced by reacting borax (sodium tetraborate) with a strong acid like hydrochloric acid:
• Na₂B₄O₇.10H₂O + 2HCl  → 4 H₃BO₃ + 2NaCl + 5H₂O
• Uses: Used in eye washes due to its antifungal and antibacterial properties, as a flame retardant, in nuclear reactors to control reactivity, and as a preservative in foods.

2. Boron Trioxide (B₂O₃)

• Properties: Glassy, hard, solid, very slightly soluble in water.
• Synthesis: Can be obtained by heating boric acid:
• 2𝐻₃𝐵𝑂₃  →  𝐵₂𝑂₃  +  3𝐻₂𝑂
• Uses: A critical ingredient in the manufacture of borosilicate glass (which has high resistance to thermal shock), and in ceramics as a flux.

3. Boron Carbide (B₄C)

• Properties: One of the hardest materials known, only slightly less hard than diamond; absorbs neutrons.
• Synthesis: Produced by reducing boron oxide with carbon in an electric arc furnace:
• 𝐵₂𝑂₃  +  3𝐶  →  𝐵₄𝐶  +  𝐶𝑂
• Uses: Used in abrasive applications, in cutting tools, and as body armor due to its high hardness and light weight.

4. Boron Trifluoride (BF₃)

• Properties: Colorless gas with a pungent odor; forms complexes with ethers.
• Synthesis: Can be made by reacting boron oxides with hydrofluoric acid:
• 𝐵₂𝑂₃  +  6𝐻𝐹  →  2𝐵𝐹₃  +  3𝐻₂𝑂
• Uses: Widely used as a catalyst in organic synthesis, particularly in Friedel-Crafts reactions, where it helps in the alkylation of aromatic compounds.

Aluminum Compounds

1. Aluminum Oxide (Al₂O₃)

• Properties: White or nearly colorless crystalline substance; extremely hard; high melting point; chemically inert.
• Synthesis: Formed by the calcination of aluminum hydroxide:
• 2𝐴𝑙(𝑂𝐻)₃  →  𝐴𝑙₂𝑂₃  +   3𝐻₂𝑂
• Uses: Crucial in the production of aluminum metal, as an abrasive due to its hardness, and as a refractory material in furnaces due to its high melting point and strength.

2. Aluminum Sulfate (Al₂(SO₄)₃)

• Properties: White crystalline solid; soluble in water; astringent taste.
• Synthesis: Produced by adding aluminum hydroxide to sulfuric acid:
• 2𝐴𝑙(𝑂𝐻)₃  +  3𝐻₂𝑆𝑂₄  →  𝐴𝑙₂(𝑆𝑂₄)₃  +  6𝐻₂𝑂
• Uses: Used in water purification for flocculation of impurities, in paper manufacturing as a sizing agent, and as a mordant in dyeing.

3. Aluminum Chloride (AlCl₃)

• Properties: White to yellowish in color, can form yellowish fumes; very hygroscopic and deliquescent.
• Synthesis: Can be synthesized by reacting aluminum with chlorine:
• 2Al + 3Cl₂   →   2AlCl₃
• Uses: Serves as a strong Lewis acid in chemical reactions; used in the production of synthetic rubber and polymers; also used in Friedel-Crafts reactions as a catalyst.

Gallium Compounds

1. Gallium Arsenide (GaAs)

• Properties: Crystalline solid with a high melting point; sensitive to mechanical and thermal shock.
• Synthesis: Produced by the direct combination of gallium and arsenic at high temperatures:
• Ga  +  As   →   GaAs
• Uses: A vital semiconductor material used in high-speed devices, including mobile phones, satellite communications, microwave point-to-point links