Ammonia radical cation (NH₃⁺) Lewis structure
7 valence electrons, trigonal planar, a charge of +1
Build NH₃⁺ step by step in the Lewis Structure Generator
What is the Lewis structure of NH₃⁺?
Ammonia radical cation, NH₃⁺, has 7 valence electrons. Nitrogen is the central atom, joined by three N−H single bonds. It carries no lone pairs. One electron is left unpaired, on the central N. Its only formal charge is +1, on the central N. N is AX₃: trigonal planar, with an ideal bond angle of 120°.
Valence electrons in NH₃⁺
| Element | Group | Valence electrons | Atoms | Electrons |
|---|---|---|---|---|
| Nitrogen | 15 | 5 | 1 | 5 |
| Hydrogen | 1 | 1 | 3 | 3 |
| Charge of 1+ | −1 | |||
| Total | 7 |
In one line: 5 + 3 × 1 − 1 = 7. Each atom brings the valence electrons its group gives it, and the positive charge takes one away for each unit.
How to draw the NH₃⁺ Lewis structure
- Count the valence electrons. Valence electrons: N 5 and each H 1, and the 1+ charge takes 1 away. 5 + 3 × 1 − 1 = 7.
- Choose the central atom. N 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 7 − 6 = 1.
- Complete the outer atoms. Every outer atom is H, and its one bond already gives it the two electrons it holds. 1 remains.
- Put the rest on the central atom. The 1 left goes on N as an unpaired electron, and N now has 7 electrons round it.
- Make multiple bonds where needed. N is left with 7 electrons, one of them unpaired. Every atom bonded to it is H, which has no lone pair to turn into a second bond, so N stays at 7.
Lone pairs and formal charges in NH₃⁺
| Atom | Number | Bonds | Lone pairs | Electrons round it | Formal charge, V − N − B/2 |
|---|---|---|---|---|---|
| N (central) | 1 | three single bonds | 0 and 1 unpaired electron | 7 | 5 − 1 − 3 = +1 |
| 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 +1, the charge on the ion.
Shape and polarity of NH₃⁺
| Central atom | N |
|---|---|
| VSEPR class | AX₃ |
| Electron geometry | trigonal planar |
| Molecular geometry | trigonal planar |
| Ideal bond angle | 120° |
| Polarity, an estimate | not applicable |
An ion carries a net charge, so whether its bond dipoles cancel is not the question polarity asks.
N 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.
Notes on the NH₃⁺ Lewis structure
- With 7 electrons one is left unpaired. It goes on the central nitrogen, since hydrogen holds only the two electrons of its bond.
- The ammonia radical cation is flat, like the methyl radical with the same seven electrons: its odd electron sits in a p orbital above and below the plane and pushes on none of the bonds, so it is trigonal planar, not the pyramid that counting the electron as a domain gives.
Work with NH₃⁺
- Lewis Structure Generator: NH₃⁺ 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