Phosphine (PH₃) Lewis structure
8 valence electrons, trigonal pyramidal
Build PH₃ step by step in the Lewis Structure Generator
What is the Lewis structure of PH₃?
Phosphine, PH₃, has 8 valence electrons. Phosphorus is the central atom, joined by three P−H single bonds. It carries one lone pair on the central P. Every formal charge is zero. P is AX₃E₁: trigonal pyramidal, with an ideal bond angle of 109.5°, and the molecule is polar.
Valence electrons in PH₃
| Element | Group | Valence electrons | Atoms | Electrons |
|---|---|---|---|---|
| Phosphorus | 15 | 5 | 1 | 5 |
| Hydrogen | 1 | 1 | 3 | 3 |
| Total | 8 |
In one line: 5 + 3 × 1 = 8. Each atom brings the valence electrons its group gives it.
How to draw the PH₃ Lewis structure
- Count the valence electrons. Valence electrons: P 5 and each H 1. 5 + 3 × 1 = 8.
- Choose the central atom. P 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 8 − 6 = 2.
- Complete the outer atoms. Every outer atom is H, and its one bond already gives it the two electrons it holds. 2 remain.
- Put the rest on the central atom. The 2 left go on the central atom as one lone pair on P, and P 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 PH₃
| Atom | Number | Bonds | Lone pairs | Electrons round it | Formal charge, V − N − B/2 |
|---|---|---|---|---|---|
| P (central) | 1 | three single bonds | 1 | 8 | 5 − 2 − 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 PH₃
| Central atom | P |
|---|---|
| VSEPR class | AX₃E₁ |
| Electron geometry | tetrahedral |
| Molecular geometry | trigonal pyramidal |
| Ideal bond angle | 109.5° |
| Polarity, an estimate | polar |
The trigonal pyramidal shape leaves the bond dipoles unbalanced.
P has three σ bonds and one lone pair, four electron domains in all, so its electron geometry is tetrahedral. Counting only the bonded atoms, the molecular geometry is trigonal pyramidal.
The VSEPR Molecular Geometry viewer turns the AX₃E₁ shape in 3D, lone pairs included.
Work with PH₃
- Lewis Structure Generator: PH₃ 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