Tetrafluoroborate ion (BF₄⁻) Lewis structure
32 valence electrons, tetrahedral, a charge of −1
Build BF₄⁻ step by step in the Lewis Structure Generator
What is the Lewis structure of BF₄⁻?
Tetrafluoroborate ion, BF₄⁻, has 32 valence electrons. Boron is the central atom, joined by four B−F single bonds. It carries three lone pairs on each F. Its only formal charge is −1, on the central B. B is AX₄: tetrahedral, with an ideal bond angle of 109.5°.
Valence electrons in BF₄⁻
| Element | Group | Valence electrons | Atoms | Electrons |
|---|---|---|---|---|
| Boron | 13 | 3 | 1 | 3 |
| Fluorine | 17 | 7 | 4 | 28 |
| Charge of 1− | +1 | |||
| Total | 32 |
In one line: 3 + 4 × 7 + 1 = 32. Each atom brings the valence electrons its group gives it, and the negative charge adds one electron for each unit.
How to draw the BF₄⁻ Lewis structure
- Count the valence electrons. Valence electrons: B 3 and each F 7, and the 1− charge adds 1. 3 + 4 × 7 + 1 = 32.
- Choose the central atom. B goes in the middle: B is the least electronegative atom other than H, χ 2.04 against 3.98 for F.
- Join the atoms with single bonds. Four single bonds use 8 electrons, leaving 32 − 8 = 24.
- Complete the outer atoms. Each outer atom takes enough lone pairs to reach eight: 4 F × 6 = 24, leaving 24 − 24 = 0.
- Put the rest on the central atom. Nothing is left, so B gets no lone pair, and B now has 8 electrons round it.
- Make multiple bonds where needed. Every atom already has an octet, so no lone pair needs to become a bond.
Lone pairs and formal charges in BF₄⁻
| Atom | Number | Bonds | Lone pairs | Electrons round it | Formal charge, V − N − B/2 |
|---|---|---|---|---|---|
| B (central) | 1 | four single bonds | 0 | 8 | 3 − 0 − 4 = −1 |
| F | 4 | one single bond | 3 | 8 | 7 − 6 − 1 = 0 |
V is the atom’s valence electrons, N its nonbonding electrons and B its bonding electrons. The formal charges add up to −1, the charge on the ion.
Shape and polarity of BF₄⁻
| Central atom | B |
|---|---|
| VSEPR class | AX₄ |
| Electron geometry | tetrahedral |
| Molecular geometry | tetrahedral |
| Ideal bond angle | 109.5° |
| Polarity, an estimate | not applicable |
An ion carries a net charge, so whether its bond dipoles cancel is not the question polarity asks.
B has four σ bonds and no lone pairs, four electron domains in all, so its electron geometry is tetrahedral. With no lone pairs, the molecular geometry is the same.
The VSEPR Molecular Geometry viewer turns the AX₄ shape in 3D, lone pairs included.
Work with BF₄⁻
- Lewis Structure Generator: BF₄⁻ 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