charge that would result on an atom by taking the number of valence electrons on the neutral atom and subtracting the nonbonding electrons and the number of bonds (one-half of the bonding electrons)

arrangement of atoms in a molecule or ion

situation in which one Lewis structure is insufficient to describe the bonding in a molecule and the average of multiple structures is observed

two or more Lewis structures that have the same arrangement of atoms but different arrangements of electrons

average of the resonance forms shown by the individual Lewis structures

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Chemistry 2e · 7.4 Formal Charges and Resonance

Formal Charges and Resonance: practice problems

10 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

Exercises 45
Write resonance forms that describe the distribution of electrons in each of these molecules or ions.
(a) sulfur dioxide, SO₂
(b) carbonate ion, $CO_{3}^{2-}$
(c) hydrogen carbonate ion, $HCO_{3}^{-}$ (C is bonded to an OH group and two O atoms)
(d) pyridine:
(e) the allyl ion:
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Exercises 47
Sodium nitrite, which has been used to preserve bacon and other meats, is an ionic compound. Write the resonance forms of the nitrite ion, $NO_{2}^{-} .$
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Exercises 49
Write the Lewis structures for the following, and include resonance structures where appropriate. Indicate which has the strongest carbon-oxygen bond.
(a) CO₂
(b) CO
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Exercises 51
Determine the formal charge of each element in the following:
(a) HCl
(b) CF₄
(c) PCl₃
(d) PF₅
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Exercises 53
Calculate the formal charge of chlorine in the molecules Cl₂, BeCl₂, and ClF₅.
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Exercises 55
Draw all possible resonance structures for each of these compounds. Determine the formal charge on each atom in each of the resonance structures:
(a) O₃
(b) SO₂
(c) $NO_{2}^{-}$
(d) $NO_{3}^{-}$
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Exercises 57
Based on formal charge considerations, which of the following would likely be the correct arrangement of atoms in hypochlorous acid: HOCl or OClH?
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Exercises 59
Draw the structure of hydroxylamine, H₃NO, and assign formal charges; look up the structure. Is the actual structure consistent with the formal charges?
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Exercises 61
Write the Lewis structure and chemical formula of the compound with a molar mass of about 70 g/mol that contains 19.7% nitrogen and 80.3% fluorine by mass, and determine the formal charge of the atoms in this compound.
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Exercises 63
Sulfuric acid is the industrial chemical produced in greatest quantity worldwide. About 90 billion pounds are produced each year in the United States alone. Write the Lewis structure for sulfuric acid, H₂SO₄, which has two oxygen atoms and two OH groups bonded to the sulfur.
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Key terms · 5

formal charge: charge that would result on an atom by taking the number of valence electrons on the neutral atom and subtracting the nonbonding electrons and the number of bonds (one-half of the bonding electrons)
molecular structure: arrangement of atoms in a molecule or ion
resonance: situation in which one Lewis structure is insufficient to describe the bonding in a molecule and the average of multiple structures is observed
resonance forms: two or more Lewis structures that have the same arrangement of atoms but different arrangements of electrons
resonance hybrid: average of the resonance forms shown by the individual Lewis structures

Learn 7.4 on the whiteboard

The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.

Read 7.4 in the textbook · This section on openstax.org

Formal Charges and Resonance: practice problems

10 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

Exercises 45

Write resonance forms that describe the distribution of electrons in each of these molecules or ions.

(a) sulfur dioxide, SO₂

(b) carbonate ion, $CO_{3}^{2-}$

(d) pyridine:

A Lewis structure depicts a hexagonal ring composed of five carbon atoms and one nitrogen atom. Each carbon atom is single bonded to a hydrogen atom.

(e) the allyl ion:

A Lewis structure shows a carbon atom single bonded to two hydrogen atoms and a second carbon atom. The second carbon atom is single bonded to a hydrogen atom and a third carbon atom. The third carbon atom is single bonded to two hydrogen atoms. The whole structure is surrounded by brackets, and there is a superscripted negative sign.

Exercises 47

Sodium nitrite, which has been used to preserve bacon and other meats, is an ionic compound. Write the resonance forms of the nitrite ion, $NO_{2}^{-} .$

Exercises 49

Write the Lewis structures for the following, and include resonance structures where appropriate. Indicate which has the strongest carbon-oxygen bond.

(a) CO₂

(b) CO

Exercises 51

Determine the formal charge of each element in the following:

(a) HCl

(b) CF₄

(d) PF₅

Exercises 53

Calculate the formal charge of chlorine in the molecules Cl₂, BeCl₂, and ClF₅.

Exercises 55

Draw all possible resonance structures for each of these compounds. Determine the formal charge on each atom in each of the resonance structures:

(a) O₃

(b) SO₂

(d) $NO_{3}^{-}$

Exercises 57

Based on formal charge considerations, which of the following would likely be the correct arrangement of atoms in hypochlorous acid: HOCl or OClH?

Exercises 59

Draw the structure of hydroxylamine, H₃NO, and assign formal charges; look up the structure. Is the actual structure consistent with the formal charges?

Exercises 61

Write the Lewis structure and chemical formula of the compound with a molar mass of about 70 g/mol that contains 19.7% nitrogen and 80.3% fluorine by mass, and determine the formal charge of the atoms in this compound.

Exercises 63

Sulfuric acid is the industrial chemical produced in greatest quantity worldwide. About 90 billion pounds are produced each year in the United States alone. Write the Lewis structure for sulfuric acid, H₂SO₄, which has two oxygen atoms and two OH groups bonded to the sulfur.

Key terms · 5

formal charge: charge that would result on an atom by taking the number of valence electrons on the neutral atom and subtracting the nonbonding electrons and the number of bonds (one-half of the bonding electrons)
molecular structure: arrangement of atoms in a molecule or ion
resonance: situation in which one Lewis structure is insufficient to describe the bonding in a molecule and the average of multiple structures is observed
resonance forms: two or more Lewis structures that have the same arrangement of atoms but different arrangements of electrons
resonance hybrid: average of the resonance forms shown by the individual Lewis structures

Learn 7.4 on the whiteboard

The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.

Read 7.4 in the textbook · This section on openstax.org