Phosphorus trichloride (PCl₃) Lewis structure
26 valence electrons, trigonal pyramidal
Build PCl₃ step by step in the Lewis Structure Generator
What is the Lewis structure of PCl₃?
Phosphorus trichloride, PCl₃, has 26 valence electrons. Phosphorus is the central atom, joined by three P−Cl single bonds. It carries one lone pair on the central P and three on each Cl. 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 PCl₃
| Element | Group | Valence electrons | Atoms | Electrons |
|---|---|---|---|---|
| Phosphorus | 15 | 5 | 1 | 5 |
| Chlorine | 17 | 7 | 3 | 21 |
| Total | 26 |
In one line: 5 + 3 × 7 = 26. Each atom brings the valence electrons its group gives it.
How to draw the PCl₃ Lewis structure
- Count the valence electrons. Valence electrons: P 5 and each Cl 7. 5 + 3 × 7 = 26.
- Choose the central atom. P goes in the middle: P is the least electronegative atom other than H, χ 2.19 against 3.16 for Cl.
- Join the atoms with single bonds. Three single bonds use 6 electrons, leaving 26 − 6 = 20.
- Complete the outer atoms. Each outer atom takes enough lone pairs to reach eight: 3 Cl × 6 = 18, leaving 20 − 18 = 2.
- 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 PCl₃
| 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 |
| Cl | 3 | 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 0, the molecule’s overall charge.
Shape and polarity of PCl₃
| 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 PCl₃
- Lewis Structure Generator: PCl₃ 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