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ScienceQuest

Methyl cation (CH₃⁺) Lewis structure

6 valence electrons, trigonal planar, a charge of +1

C H H H + +
CH₃⁺ as the Lewis Structure Generator draws it: lone pairs as dots, nonzero formal charges circled.

Build CH₃⁺ step by step in the Lewis Structure Generator

What is the Lewis structure of CH₃⁺?

Methyl cation, CH₃⁺, has 6 valence electrons. Carbon is the central atom, joined by three C−H single bonds. It carries no lone pairs. Its only formal charge is +1, on the central C. C is AX₃: trigonal planar, with an ideal bond angle of 120°.

Valence electrons in CH₃⁺

Element Group Valence electrons Atoms Electrons
Carbon 14 4 1 4
Hydrogen 1 1 3 3
Charge of 1+ −1
Total 6

In one line: 4 + 3 × 1 − 1 = 6. Each atom brings the valence electrons its group gives it, and the positive charge takes one away for each unit.

How to draw the CH₃⁺ Lewis structure

  1. Count the valence electrons. Valence electrons: C 4 and each H 1, and the 1+ charge takes 1 away. 4 + 3 × 1 − 1 = 6.
  2. Choose the central atom. C 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. Three single bonds use 6 electrons, leaving 6 − 6 = 0.
  4. Complete the outer atoms. Every outer atom is H, and its one bond already gives it the two electrons it holds. 0 remain.
  5. Put the rest on the central atom. Nothing is left, so C gets no lone pair, and C now has 6 electrons round it.
  6. Make multiple bonds where needed. C is left with 6 electrons. Every atom bonded to it is H, which has no lone pair to turn into a second bond, so C stays short, as its +1 formal charge records.

Lone pairs and formal charges in CH₃⁺

Atom Number Bonds Lone pairs Electrons round it Formal charge, V − N − B/2
C (central) 1 three single bonds 0 6 4 − 0 − 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 CH₃⁺

Central atom C
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.

C 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.

Work with CH₃⁺