Reactivity of the Boron Family (Group 13) Elements: Reactions with Water and Halogens

Boron Family (Group 13) Reactions

Introduction to Boron Family Reactivity

The Boron Family (Group 13 elements) includes boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (Tl). Their chemical reactivity is primarily determined by the presence of three valence electrons in the ns2np1 configuration. These elements commonly exhibit a +3 oxidation state, though heavier members may also show a +1 state due to the inert pair effect.

• Valence electrons: 3 (in s and p subshells)

• Common reactions: With water (H2O) and halogens (X2)

Reactions with Water

Most Boron Family metals do not react with water under normal conditions, but some, such as aluminum, can react with steam to form metal oxides and hydrogen gas.

General Reaction with H2O (Steam): $2M(s) + 6H_2O(g) \rightarrow 2M(OH)_3(s) + 3H_2(g)$ where M = Group 13 metal (e.g., Al, Ga, In)

• Exception: Thallium (Tl) possesses a +1 oxidation state and behaves differently.

Example: Complete and balance the following reaction:

• $2\text{Ga}(s) + 6\text{H}_2\text{O}(g) \rightarrow 2\text{Ga}(OH)_3(s) + 3\text{H}_2(g)$

Reactions with Halogens

The Boron Family metals react with halogens (such as Cl2, Br2, I2) to form trihalides, which are typically ionic or covalent depending on the metal and halogen involved.

General Reaction with Halogens: $2M(s) + 3X_2(g) \rightarrow 2MX_3(s)$ where M = Group 13 metal, X = halogen

Example: Provide the products from the reaction between strontium and aqueous chlorine:

• $2\text{Al}(s) + 3\text{Cl}_2(g) \rightarrow 2\text{AlCl}_3(s)$

Summary Table: Boron Family Reactions

Element	Reaction with H2O	Reaction with Halogens
Boron (B)	No reaction	Forms BX3 (covalent)
Aluminum (Al)	Reacts with steam: $2Al + 6H_2O \rightarrow 2Al(OH)_3 + 3H_2$	Reacts: $2Al + 3X_2 \rightarrow 2AlX_3$
Gallium (Ga)	Reacts with steam	Reacts: $2Ga + 3X_2 \rightarrow 2GaX_3$
Indium (In)	Reacts with steam	Reacts: $2In + 3X_2 \rightarrow 2InX_3$
Thallium (Tl)	Limited reactivity; +1 state common	Forms TlX and TlX3

Key Points:

• Group 13 elements generally form +3 oxidation state compounds, but heavier elements may also form +1 compounds.

• Reactivity with water increases down the group, but boron does not react with water.

• All Group 13 metals react with halogens to form trihalides.

Additional info: The reactivity of these elements is influenced by their atomic size, ionization energy, and the inert pair effect, especially for thallium.