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Ch.9 - Molecular Geometry and Bonding Theories
Chapter 9, Problem 65c

In the formate ion, HCO2-, the carbon atom is the central atom with the other three atoms attached to it. (c) Are there multiple equivalent resonance structures for the ion?

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Identify the atoms and their valence electrons: Carbon (C) has 4 valence electrons, Oxygen (O) has 6 valence electrons, and Hydrogen (H) has 1 valence electron. The ion has an overall charge of -1, adding one more electron to the total count.
Calculate the total number of valence electrons: Add the valence electrons from all atoms and the extra electron due to the negative charge.
Draw the Lewis structure: Place the carbon atom in the center, attach the hydrogen atom and the two oxygen atoms to it, and distribute the electrons to satisfy the octet rule for each atom.
Check for resonance structures: Determine if the electrons can be rearranged to form different but equivalent structures by moving electrons between the oxygen atoms and the carbon atom.
Conclude about resonance: If multiple equivalent structures can be drawn by shifting electrons without changing the positions of the atoms, then the ion has resonance structures.

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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 with resonance, the actual structure is a hybrid of these forms, which helps to represent the distribution of electrons more accurately. For the formate ion, HCO2-, resonance structures show how the double bond can be between carbon and either of the two oxygen atoms.
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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 molecular geometry. In the case of the formate ion, drawing the Lewis structure helps identify the possible resonance forms and the formal charges on each atom.
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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 electrons. It helps in determining the most stable resonance structure, as the most stable structure typically has the lowest formal charges. In the formate ion, analyzing formal charges can clarify the equivalence of the resonance structures.
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