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ScienceQuest

Amide ion (NH₂⁻) Lewis structure

8 valence electrons, bent, a charge of −1

N H H − −
NH₂⁻ as the Lewis Structure Generator draws it: lone pairs as dots, nonzero formal charges circled.

Build NH₂⁻ step by step in the Lewis Structure Generator

What is the Lewis structure of NH₂⁻?

Amide ion, NH₂⁻, has 8 valence electrons. Nitrogen is the central atom, joined by two N−H single bonds. It carries two lone pairs on the central N. Its only formal charge is −1, on the central N. N is AX₂E₂: bent, with an ideal bond angle of 109.5°.

Valence electrons in NH₂⁻

Element Group Valence electrons Atoms Electrons
Nitrogen 15 5 1 5
Hydrogen 1 1 2 2
Charge of 1− +1
Total 8

In one line: 5 + 2 × 1 + 1 = 8. Each atom brings the valence electrons its group gives it, and the negative charge adds one electron for each unit.

How to draw the NH₂⁻ Lewis structure

  1. Count the valence electrons. Valence electrons: N 5 and each H 1, and the 1− charge adds 1. 5 + 2 × 1 + 1 = 8.
  2. 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.
  3. Join the atoms with single bonds. Two single bonds use 4 electrons, leaving 8 − 4 = 4.
  4. Complete the outer atoms. Every outer atom is H, and its one bond already gives it the two electrons it holds. 4 remain.
  5. Put the rest on the central atom. The 4 left go on the central atom as two lone pairs on N, and N now has 8 electrons round it.
  6. 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 NH₂⁻

Atom Number Bonds Lone pairs Electrons round it Formal charge, V − N − B/2
N (central) 1 two single bonds 2 8 5 − 4 − 2 = −1
H 2 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 NH₂⁻

Central atom N
VSEPR class AX₂E₂
Electron geometry tetrahedral
Molecular geometry bent
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.

N has two σ bonds and two lone pairs, four electron domains in all, so its electron geometry is tetrahedral. Counting only the bonded atoms, the molecular geometry is bent.

The VSEPR Molecular Geometry viewer turns the AX₂E₂ shape in 3D, lone pairs included.

Work with NH₂⁻