# What are the formal charges in "O"_3 (ozone)?

Dec 1, 2015

$- 1 , 0 , 1$

#### Explanation:

A formal charge is equal to the number of valence electrons of an atom MINUS the number of electrons assigned to an atom.

Consider the resonance structures for ${\text{O}}_{3}$.

Oxygen has $6$ valence electrons. Look at the top left oxygen atom. It has two lone pairs ($4$ electrons) and a double bond ($2$ electrons).

Even though a double bond contains $4$ electrons total and is counted as such when seeing that oxygen's octet is filled, $2$ electrons belong to each oxygen and they are shared among the two.

Let's examine the top resonance structure:

Left: $6$ valence $- 6$ assigned =color(blue)(0 formal charge
Center $6$ valence $- 5$ assigned =color(blue)(1 formal charge
Right: $6$ valence $- 7$ assigned $= \textcolor{b l u e}{- 1}$ formal charge

Notice that even though the atoms have varying formal charges, the overall charge of ${\text{O}}_{3}$ is the sum of the formal charges in the molecule: $0 + 1 + \left(- 1\right) = 0$.

Ions' formal charge sums are $\ne 0$.