Group 13 Elements: The Boron Family — Core Principles
Core Principles
Group 13 elements, the Boron family (B, Al, Ga, In, Tl), are p-block elements with a general electronic configuration of . They typically exhibit a +3 oxidation state. However, due to the inert pair effect, the stability of the +1 oxidation state increases down the group, becoming predominant for Thallium.
Boron is a non-metal, showing anomalous behavior due to its small size, high ionization enthalpy, and absence of d-orbitals, leading to covalent, electron-deficient compounds like diborane () with unique 3c-2e 'banana bonds'.
Boric acid () is a weak monobasic Lewis acid. Aluminium is a metal but amphoteric, reacting with both acids and bases. Trends in atomic radii and ionization enthalpy are irregular due to the poor shielding of d and f electrons in heavier elements.
Key compounds include borax, boric acid, diborane, and aluminium oxide/chloride. Lewis acid character is prominent, with being the weakest among boron trihalides due to back-bonding.
Often confused with
Side-by-side differences the NEET paper likes to test.
| Aspect | Group 13 Elements: The Boron Family | Aluminium |
|---|---|---|
| Nature | Non-metal | Metal |
| Physical State | Hard, black solid (amorphous) or crystalline | Soft, silvery-white solid |
| Oxidation State | Predominantly +3, but often electron-deficient | Exclusively +3 in stable compounds |
| Covalency | Maximum covalency of 4 (due to absence of d-orbitals) | Can exhibit covalency of 4 or 6 (due to presence of vacant d-orbitals) |
| Oxides | Acidic ($B_2O_3$) | Amphoteric ($Al_2O_3$) |
| Hydroxides | Weak Lewis acid ($B(OH)_3$) | Amphoteric ($Al(OH)_3$) |
| Halides | Monomeric, strong Lewis acids ($BF_3$) | Dimeric ($Al_2Cl_6$) in vapor, polymeric in solid, strong Lewis acids |
Boron, the first member of Group 13, stands in stark contrast to Aluminium, its immediate successor. Boron is a non-metal, forming predominantly covalent and electron-deficient compounds, with a maximum covalency of four due to the absence of d-orbitals.
Its oxide is acidic, and boric acid acts as a Lewis acid. Aluminium, on the other hand, is a typical metal, though amphoteric, and can expand its covalency to six by utilizing its vacant d-orbitals. These fundamental differences highlight the anomalous behavior of Boron within its own group, a common trend for the first element of many p-block groups.
Why it is tested: For NEET, understanding the distinct properties of Boron versus Aluminium is crucial. Questions often test the anomalous behavior of Boron, its electron-deficient nature, Lewis acidity, and the differences in bonding and reactivity compared to Aluminium. The amphoteric nature of Aluminium and its compounds is also a frequently tested concept, making this comparison highly relevant for conceptual clarity and problem-solving.