Ch.10 - Chemical Bonding I: The Lewis Model

Problem 78

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Chapter 10, Problem 78

What are the formal charges of the atoms shown in red?

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Step 1: Identify the valence electrons for each atom in its neutral state. Sulfur (S) has 6 valence electrons, and Nitrogen (N) has 5 valence electrons.

Step 2: Count the electrons around each atom in the given structure. For Sulfur (S+), count the bonding and lone pair electrons. For Nitrogen (N), do the same.

Step 3: Calculate the formal charge using the formula: Formal Charge = (Valence Electrons) - (Non-bonding Electrons) - (Bonding Electrons / 2).

Step 4: Apply the formula to Sulfur (S+). Sulfur has 6 valence electrons, 4 non-bonding electrons, and 4 bonding electrons (2 bonds).

Step 5: Apply the formula to Nitrogen (N). Nitrogen has 5 valence electrons, 2 non-bonding electrons, and 6 bonding electrons (3 bonds).

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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 bonds, and the number of non-bonding electrons. It helps in determining the most stable Lewis structure for a molecule. The formula for calculating formal charge is: Formal Charge = (Valence Electrons) - (Non-bonding Electrons) - (1/2 * Bonding Electrons).

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 provide a visual representation of the arrangement of electrons and help in predicting the geometry and reactivity of the molecule. Understanding how to draw and interpret Lewis structures is essential for analyzing molecular properties and charges.

Resonance Structures

Resonance structures are different Lewis structures that represent the same molecule, differing only in the placement of electrons. They illustrate the delocalization of electrons within a molecule, which can affect the stability and reactivity of the compound. Recognizing resonance is crucial for understanding the distribution of formal charges and the overall electronic structure of the molecule.

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Resonance Structures

Related Practice

Draw the Lewis structure (including resonance structures) for the acetate ion (CH₃COO^-). For each resonance structure, assign formal charges to all atoms that have formal charge.

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Textbook Question

Draw the Lewis structure (including resonance structures) for methyl azide (CH₃N₃). For each resonance structure, assign formal charges to all atoms that have formal charge.