Borane (BH₃) Lewis structure
6 valence electrons, trigonal planar
Build BH₃ step by step in the Lewis Structure Generator
What is the Lewis structure of BH₃?
Borane, BH₃, has 6 valence electrons. Boron is the central atom, joined by three B−H single bonds. It carries no lone pairs. Every formal charge is zero. B is AX₃: trigonal planar, with an ideal bond angle of 120°, and the molecule is nonpolar.
Valence electrons in BH₃
In one line: 3 + 3 × 1 = 6. Each atom brings the valence electrons its group gives it.
How to draw the BH₃ Lewis structure
- Count the valence electrons. Valence electrons: B 3 and each H 1. 3 + 3 × 1 = 6.
- Choose the central atom. B is the only atom other than H, and H is never in the middle, since it holds only two electrons and so makes one bond.
- Join the atoms with single bonds. Three single bonds use 6 electrons, leaving 6 − 6 = 0.
- Complete the outer atoms. Every outer atom is H, and its one bond already gives it the two electrons it holds. 0 remain.
- Put the rest on the central atom. Nothing is left, so B gets no lone pair, and B now has 6 electrons round it.
- Make multiple bonds where needed. B is left with 6 electrons. Every atom bonded to it is H, which has no lone pair to turn into a second bond, so B stays short, one of the known exceptions to the octet rule.
Lone pairs and formal charges in BH₃
| Atom | Number | Bonds | Lone pairs | Electrons round it | Formal charge, V − N − B/2 |
|---|---|---|---|---|---|
| B (central) | 1 | three single bonds | 0 | 6 | 3 − 0 − 3 = 0 |
| H | 3 | one single bond | 0 | 2 | 1 − 0 − 1 = 0 |
V is the atom’s valence electrons, N its nonbonding electrons and B its bonding electrons. The formal charges add up to 0, the molecule’s overall charge.
Shape and polarity of BH₃
| Central atom | B |
|---|---|
| VSEPR class | AX₃ |
| Electron geometry | trigonal planar |
| Molecular geometry | trigonal planar |
| Ideal bond angle | 120° |
| Polarity, an estimate | nonpolar |
In a trigonal planar shape identical bonds cancel exactly.
B has three σ bonds and no lone pairs, three electron domains in all, so its electron geometry is trigonal planar. With no lone pairs, the molecular geometry is the same.
The VSEPR Molecular Geometry viewer turns the AX₃ shape in 3D, lone pairs included.
Work with BH₃
- Lewis Structure Generator: BH₃ built step by step, with every formal charge worked out
- VSEPR Molecular Geometry: every VSEPR shape in 3D, with its bond angles
- All 78 Lewis structures: valence electrons, resonance, shape and polarity in one table