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Ch.8 - Basic Concepts of Chemical Bonding
Chapter 8, Problem 90

Calculate the formal charge on the indicated atom in each of the following molecules or ions: (a) the central oxygen atom in O3 (b) phosphorus in PF6- (c) nitrogen in NO2 (d) iodine in ICl3 (e) chlorine in HClO4 (hydrogen is bonded to O).

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To calculate the formal charge on an atom, use the formula: Formal Charge = (Valence Electrons) - (Non-bonding Electrons) - (Bonding Electrons / 2).
For (a) the central oxygen atom in O3: Determine the number of valence electrons for oxygen, count the non-bonding electrons (lone pairs) on the central oxygen, and count the bonding electrons (shared in bonds) around it.
For (b) phosphorus in PF6-: Identify the valence electrons for phosphorus, count the non-bonding electrons, and the bonding electrons shared with fluorine atoms. Remember to account for the negative charge on the ion.
For (c) nitrogen in NO2: Find the valence electrons for nitrogen, count the non-bonding electrons, and the bonding electrons shared with oxygen atoms. Consider the resonance structures if applicable.
For (d) iodine in ICl3 and (e) chlorine in HClO4: Follow the same process by identifying the valence electrons, counting non-bonding electrons, and bonding electrons. For HClO4, note that hydrogen is bonded to oxygen, affecting the electron count around chlorine.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Formal Charge

Formal charge is a theoretical charge assigned to an atom in a molecule, calculated based on the number of valence electrons, the number of non-bonding electrons, and half the number of bonding electrons. It helps in determining the most stable structure of a molecule by minimizing the formal charges across the atoms. The formula for calculating formal charge is: Formal Charge = Valence Electrons - (Non-bonding Electrons + 1/2 Bonding Electrons).
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Lewis Structures

Lewis structures are diagrams that represent the bonding between atoms in a molecule and the lone pairs of electrons that may exist. They are essential for visualizing the arrangement of electrons and understanding how atoms share or transfer electrons to form bonds. Drawing accurate Lewis structures is crucial for calculating formal charges, as it provides a clear picture of the electron distribution in the molecule.
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Resonance Structures

Resonance structures are different Lewis structures that represent the same molecule, where the arrangement of electrons differs but the arrangement of atoms remains the same. They are used to depict delocalized electrons that cannot be represented by a single Lewis structure. Understanding resonance is important for accurately determining formal charges, as the actual charge distribution in a molecule may be an average of multiple resonance forms.
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Related Practice
Textbook Question

A major challenge in implementing the 'hydrogen economy' is finding a safe, lightweight, and compact way of storing hydrogen for use as a fuel. The hydrides of light metals are attractive for hydrogen storage because they can store a high weight percentage of hydrogen in a small volume. For example, NaAlH4 can release 5.6% of its mass as H2 upon decomposing to NaH(s), Al(s), and H2(g). NaAlH4 possesses both covalent bonds, which hold polyatomic anions together, and ionic bonds. (d) What is the formal charge on hydrogen in the polyatomic ion?

Textbook Question

Although I3- is a known ion, F3- is not. (b) One of your classmates says that F3- does not exist because F is too electronegative to make bonds with another atom. Give an example that proves your classmate is wrong.

Textbook Question

Although I3- is a known ion, F3- is not. (c) Another classmate says F3- does not exist because it would violate the octet rule. Is this classmate possibly correct?

Textbook Question

The hypochlorite ion, ClO-, is the active ingredient in bleach. The perchlorate ion, ClO4-, is a main component of rocket propellants. Draw Lewis structures for both ions. (b) What is the formal charge of Cl in the perchlorate ion, assuming the Cl—O bonds are all single bonds?

Textbook Question

The hypochlorite ion, ClO-, is the active ingredient in bleach. The perchlorate ion, ClO4-, is a main component of rocket propellants. Draw Lewis structures for both ions. (c) What is the oxidation number of Cl in the hypochlorite ion? (d) What is the oxidation number of Cl in the perchlorate ion, assuming the Cl—O bonds are all single bonds?

Textbook Question

The following three Lewis structures can be drawn for N2O:

(a) Using formal charges, which of these three resonance forms is likely to be the most important?