3.4.1: Formal Charge and Oxidation State (Problems)

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PROBLEM \(\PageIndex{1}\)

Determine the formal charge and oxidation state of each element in the following:

a. HCl
b. CF₄
c. PCl₃

Answer a

FC: H: 0, Cl: 0

OX: H: +1, Cl: -1

Answer b

FC: C: 0, F: 0

OX: C: +4, F: -1

Answer c

FC: P: 0, Cl: 0

OX: P: +3, Cl: -1

PROBLEM \(\PageIndex{2}\)

Determine the formal charge and oxidation state of each element in the following:

a. H₃O⁺
b. \(\ce{SO4^2-}\)
c. NH₃
d. \(\ce{O2^2-}\)
e. H₂O₂

Answer a

FC: H: 0, O: +1

OX: H: +1, O: -2

Answer b

FC: S: +2, O: -1

OX: S: +6, O: -2

Answer c

FC: N: 0, H: 0

OX: N: -3, H: +1

Answer d

FC: -1

OX: -1

Answer e

FC: O: 0, H: 0

OX: O: -1, H: +1

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PROBLEM \(\PageIndex{3}\)

Calculate the formal charge and oxidation state of chlorine in the molecules Cl₂and CCl4.

Answer

FC: Cl in Cl₂: 0; Cl in CCl₄: 0

OX: Cl in Cl₂: 0; Cl in CCl₄: -1

PROBLEM \(\PageIndex{4}\)

Calculate the formal charge and oxidation state of each element in the following compounds and ions:

a. F₂CO
b. NO^–
c. \(\ce{BF4-}\)
d. \(\ce{SnCl3-}\)
e. H₂CCH₂
f. \(\ce{PO4^3-}\)

Answer a

FC: C: 0, F :0, O: 0

OX: C: +4, F: -1, O: -2

Answer b

FC: N: -1, O: 0

OX: N: +1, O: -2

Answer c

FC: B: -1, F: 0

OX: B: +3, F: -1

Answer d

FC: Sn: -1; Cl: 0

OX: Sn: +2, Cl: -1

Answer e

FC: C: 0, H: 0

OX: C: -2, H: +1

Answer f

FC: P: +1, O: -1

OX: P: +5, O: -2

PROBLEM \(\PageIndex{5}\)

Based on formal charge considerations, which of the following would likely be the correct arrangement of atoms in nitrosyl chloride: ClNO or ClON?

Answer: ClNO

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PROBLEM \(\PageIndex{6}\)

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

Answer: HOCl

PROBLEM \(\PageIndex{7}\)

Based on formal charge considerations, which of the following would likely be the correct arrangement of atoms in sulfur dioxide: OSO or SOO?

Answer: OSO

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PROBLEM \(\PageIndex{8}\)

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

Answer

The structure that gives zero formal charges is consistent with the actual structure:

A Lewis structure shows a nitrogen atom with one lone pair of electrons single bonded to two hydrogen atoms and an oxygen atom which has two lone pairs of electrons. The oxygen atom is single bonded to a hydrogen atom.

PROBLEM \(\PageIndex{9}\)

Which of the following structures would we expect for nitrous acid? Determine the formal charges:

Answer: The first structure is the best structure. the formal charges are closest to 0 (and also the second structure does not give a complete octet on N)

Contributors

Paul Flowers (University of North Carolina - Pembroke), Klaus Theopold (University of Delaware) and Richard Langley (Stephen F. Austin State University) with contributing authors. Textbook content produced by OpenStax College is licensed under a Creative Commons Attribution License 4.0 license. Download for free at http://cnx.org/contents/85abf193-2bd...a7ac8df6@9.110).
Adelaide Clark, Oregon Institute of Technology

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