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Ch.8 - Basic Concepts of Chemical Bonding
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
All textbooksBrown 14th EditionCh.8 - Basic Concepts of Chemical BondingProblem 54b
Chapter 8, Problem 54b

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?

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insert step 1> Identify the central atom in the formate ion, HCO_2^-. In this case, the central atom is carbon (C).
insert step 2> Draw the Lewis structure for the formate ion. Start by arranging the atoms with carbon in the center, hydrogen (H) and two oxygen (O) atoms bonded to it.
insert step 3> Count the total number of valence electrons available. Carbon has 4, each oxygen has 6, and hydrogen has 1. The negative charge adds an extra electron, making a total of 18 valence electrons.
insert step 4> Distribute the electrons to satisfy the octet rule for each atom, starting with the outer atoms (oxygen) and then the central atom (carbon).
insert step 5> Determine if resonance structures are needed by checking if there are multiple ways to arrange the electrons while maintaining the same arrangement of atoms. In the case of the formate ion, consider if the double bond can be placed between carbon and either oxygen atom, indicating resonance.

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Key Concepts

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

Resonance Structures

Resonance structures are different ways of drawing the same molecule that illustrate the delocalization of electrons. In molecules where multiple valid Lewis structures can be drawn, resonance helps to represent the actual distribution of electrons more accurately. The true structure is a hybrid of these resonance forms, which can affect the stability and reactivity of the molecule.
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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 provide a visual way to understand how atoms are connected and the arrangement of electrons. For the formate ion, drawing the Lewis structure helps to identify the presence of resonance by showing how electrons can be distributed differently among the atoms.
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Formal Charge

Formal charge is a concept used to determine the distribution of electrons in a molecule and to assess the stability of different resonance structures. It is calculated by taking the number of valence electrons in an atom, subtracting the number of non-bonding electrons, and half the number of bonding electrons. A lower formal charge on atoms typically indicates a more stable structure, guiding the selection of the most significant resonance forms.
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Related Practice
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. (c) Would you predict that the C—O bond lengths in the formate ion would be longer or shorter relative to those in CO2?

Textbook Question

For each of the following molecules or ions of sulfur and oxygen, write a single Lewis structure that obeys the octet rule, and calculate the oxidation numbers and formal charges on all the atoms: (a) SO2 Write a single Lewis structure that obeys the octet rule for SO2 and assign the formal charges on all the atoms. (b) SO3 Write a single Lewis structure that obeys the octet rule for SO3 and assign the formal charges on all the atoms. (c) SO32- Write a single Lewis structure that obeys the octet rule for SO32- and assign the formal charges on all the atoms.

Textbook Question

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

Textbook Question

(c) What would you predict for the lengths of the bonds in NO2- relative to N¬O single bonds and double bonds?

Textbook Question

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

Textbook Question

Based on Lewis structures, predict the ordering, from shortest to longest, of N¬O bond lengths in NO+, NO2-, and NO3-.

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