Multiple Choice
What is the charge on the carbonate ion?
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3. Chemical Reactions
Polyatomic Ions
Multiple Choice
Which of the following is the correct Lewis structure for the formate ion, CHO2-, including its formal charges?
A
A central carbon atom double-bonded to both oxygens and single-bonded to a hydrogen atom.
B
A central carbon atom single-bonded to two oxygens (each with a negative charge) and single-bonded to a hydrogen atom.
C
A central carbon atom single-bonded to a hydrogen atom and triple-bonded to one oxygen atom.
D
A central carbon atom double-bonded to one oxygen, single-bonded to another oxygen (with a negative charge), and single-bonded to a hydrogen atom.
Verified step by step guidance1
Step 1: Determine the total number of valence electrons for the formate ion (CHO2-). Carbon has 4 valence electrons, hydrogen has 1, each oxygen has 6, and the negative charge adds 1 extra electron. So, total valence electrons = 4 + 1 + (2 × 6) + 1 = 18 electrons.
Step 2: Arrange the atoms with carbon as the central atom, since it is less electronegative than oxygen. Connect the carbon to the hydrogen and both oxygens with single bonds initially.
Step 3: Distribute the remaining electrons to satisfy the octet rule for the oxygen atoms first, placing lone pairs on oxygens to complete their octets. Remember that hydrogen only needs 2 electrons.
Step 4: To minimize formal charges, form a double bond between the carbon and one oxygen atom. Calculate formal charges using the formula: \(\text{Formal charge} = \text{Valence electrons} - \text{Nonbonding electrons} - \frac{1}{2} \times \text{Bonding electrons}\) for each atom.
Step 5: Confirm that the Lewis structure has the lowest possible formal charges, with the negative charge localized on the single-bonded oxygen, and that the carbon has no formal charge, matching the correct structure described.
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