Group 13 Elements: The Boron Family

Group 13: The Boron Family

Group 13 consists of boron (B), aluminium (Al), gallium (Ga), indium (In) and thallium (Tl). This is one of the most chemically diverse groups in the periodic table — boron behaves as a typical non-metal, aluminium is a metal that still shares a good deal of chemistry with boron (a "diagonal-relationship"-like kinship within the same group), while gallium, indium and thallium are essentially pure metals.

Occurrence of boron. Boron is scarce, making up less than 0.0001% of the earth's crust by mass. It is never found free; it occurs combined as:

• Orthoboric acid, $H_3BO_3$
• Borax, $Na_2B_4O_7 \cdot 10H_2O$
• Kernite, $Na_2B_4O_7 \cdot 4H_2O$

In India, borax is mined from the Puga Valley in Ladakh and from Sambhar Lake in Rajasthan. Natural boron is a mixture of two isotopes, $^{10}B$ (~19%) and $^{11}B$ (~81%).

Occurrence of aluminium. Aluminium is far more abundant — it is the most plentiful metal in the earth's crust and the third most abundant element overall (8.3% by mass), ranking behind only oxygen (45.5%) and silicon (27.7%). Its chief ores are bauxite ($Al_2O_3 \cdot 2H_2O$) and cryolite ($Na_3AlF_6$); in India it also occurs as mica-associated deposits in Madhya Pradesh, Karnataka, Orissa and Jammu. Gallium, indium and thallium are all much rarer than boron and aluminium.

Table 11.1 — General Electronic Configuration and Oxidation States across the p-Block

This table sets the pattern the rest of the chapter follows: every p-block group's "textbook" oxidation state equals the number of $ns^2np^x$ valence electrons, but heavier members increasingly favour an oxidation state two units lower — the seed of the inert-pair effect discussed later in this chapter.