Group 13 — Boron Compounds — Notes

Cue Column	Note Column
Diborane formula?	$B_{2}H_{6}$
Bridging bonds in $B_{2}H_{6}$ ?	Two 3-centre-2-electron (3c-2e) banana bonds; each involves 2B + 1H
Terminal bonds in $B_{2}H_{6}$ ?	Four normal 2c-2e B-H bonds (2 per boron)
Borax formula?	$Na_{2}B_{4}O_{7}$ · $10H_{2}O$
Borax structural units?	Two $BO_{3}$ (trigonal planar) + Two $BO_{4}$ (tetrahedral)
Borax bead test?	Heated borax forms glassy $B_{2}O_{3}$ ; dissolves metal oxide to give coloured metaborate
Boric acid formula?	$H_{3}$$BO_{3}$
$H_{3}$$BO_{3}$ acidity type?	Lewis acid: accepts $OH^{-}$ from $H_{2}O$ → [B(OH)_{4}]^{-} + $H^{+}$
$H_{3}$$BO_{3}$ structure?	Planar layers held by O-H···O hydrogen bonds between adjacent molecules
$AlCl_{3}$ — why dimer?	Al is electron-deficient (6e); forms $Al_{2}Cl_{6}$ by coordinate bonds Al←Cl
Inert pair effect?	Thallium (Tl) most prominently shows +1 state due to inert 6 $s^{2}$ pair

Summary: Boron is anomalous — all its compounds are covalent and electron-deficient. $B_{2}H_{6}$ with 3c-2e banana bonds, $H_{3}$$BO_{3}$ as a Lewis acid, and $Al_{2}Cl_{6}$ dimer formation are top NEET targets. Borax bead test is a classic identification technique.