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Ch.8 - Basic Concepts of Chemical Bonding
All textbooksBrown 15th EditionCh.8 - Basic Concepts of Chemical BondingProblem 59
Chapter 8, Problem 59

Consider a Lewis structure for SO3 that satisfies the octet rule. Which of the following statements is or are true?
i. SO3 has three equivalent resonance structures.
ii. There are one shorter and two longer S—O bond lengths in SO3.
iii. The S atom in SO3 has a nonzero formal charge.

Verified step by step guidance
1
Step 1: Draw the Lewis structure for \( \text{SO}_3 \). Start by counting the total number of valence electrons. Sulfur (S) has 6 valence electrons, and each oxygen (O) also has 6 valence electrons. Therefore, \( \text{SO}_3 \) has a total of \( 6 + 3 \times 6 = 24 \) valence electrons.
Step 2: Arrange the atoms with sulfur in the center and the three oxygen atoms surrounding it. Distribute the electrons to satisfy the octet rule for each atom. Initially, connect each oxygen to sulfur with a single bond, using 6 electrons (2 per bond).
Step 3: Distribute the remaining 18 electrons to complete the octets of the oxygen atoms. Each oxygen will need 6 more electrons to complete its octet, using up all 18 remaining electrons.
Step 4: Check the formal charges. The formal charge is calculated as: \( \text{Formal Charge} = \text{Valence Electrons} - \text{Non-bonding Electrons} - \frac{1}{2} \times \text{Bonding Electrons} \). Calculate the formal charges for sulfur and each oxygen atom.
Step 5: Consider resonance structures. Since the sulfur can form double bonds with each oxygen, there are three equivalent resonance structures where the double bond is with a different oxygen each time. This results in all S—O bonds being equivalent in length, and the formal charge on sulfur being zero.

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Key Concepts

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

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 help visualize the arrangement of electrons and the connectivity of atoms, allowing chemists to predict molecular geometry and reactivity. In the case of SO3, drawing its Lewis structure involves ensuring that the octet rule is satisfied for each atom, particularly the sulfur and oxygen atoms.
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Resonance Structures

Resonance structures are different ways of drawing the same molecule that illustrate the delocalization of electrons. In SO3, resonance structures show that the double bonds between sulfur and oxygen can be distributed among the three S—O bonds, leading to equivalent structures. This concept is crucial for understanding the stability and properties of molecules that cannot be accurately represented by a single Lewis structure.
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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 bonds, and the number of lone pair electrons. It helps assess the stability of a molecule and the distribution of electrons. In SO3, calculating the formal charge on the sulfur atom reveals whether it carries a charge, which is important for understanding the molecule's reactivity and resonance.
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Related Practice
Textbook Question

(b) With what allotrope of oxygen is it isoelectronic?

Textbook Question

Consider the formate ion, HCO2-, which is the anion formed when formic acid loses an H+ ion. The H and the two O atoms are bonded to the central C atom. (b) Are resonance structures needed to describe the structure?

Textbook Question

Predict the ordering, from shortest to longest, of the bond lengths in CO, CO2, and CO32- .

Textbook Question

Which of the following statements about benzene, C6H6, is or are true?

i. Benzene has two equivalent resonance structures.

ii. There are no nonbonding pairs in the Lewis structure for benzene.

iii. Benzene has three short and three long C—C bonds.

Textbook Question

b. Which of these compounds or ions is an exception to the octet rule: nitrogen dioxide, borohydride (BH4−), borazine (B3N3H6 which is analogous to benzene with alternating B and N in the ring), or boron trichloride?