# What is the formal charge on the sulfur atom in sulfur trioxide SO_3?

Sep 16, 2016

Good question. In most treatments the formal charge is $+ 2$.

#### Explanation:

Sulfur assumes a $+ V I$ oxidation state in the acid anhydride sulfur trioxide, and of course has the same oxidation state in sulfuric acid.

$\left(O =\right) {S}^{2 +} {\left(- {O}^{-}\right)}_{2}$

Most chemists would settle for the given representation.

The molecule is of course trigonal planar with ${D}_{3 h}$ symmetry.