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

1 Answer
mason m
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.

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Consider the resonance structures for "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 =color(blue)(-1) formal charge

Notice that even though the atoms have varying formal charges, the overall charge of "O"_3 is the sum of the formal charges in the molecule: 0+1+(-1)=0.

Ions' formal charge sums are !=0.

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