Multiple Choice
In the Lewis dot structure of AsCl_3, how many lone pairs of electrons are present on the As atom?
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11. Bonding & Molecular Structure
Lewis Dot Structures: Ions
Multiple Choice
Which of the following is the best Lewis dot structure for the fulminate ion, CNO^-?
A
C has a triple bond to N, N has a single bond to O; C: no lone pairs, N: one lone pair, O: three lone pairs; negative charge on O.
B
C has a double bond to N, N has a double bond to O; C: one lone pair, N: one lone pair, O: two lone pairs; negative charge on N.
C
C has a single bond to N, N has a triple bond to O; C: two lone pairs, N: no lone pairs, O: one lone pair; negative charge on C.
D
C has a single bond to N, N has a single bond to O; C: three lone pairs, N: two lone pairs, O: three lone pairs; negative charge delocalized over all atoms.
Verified step by step guidance1
Step 1: Determine the total number of valence electrons for the fulminate ion (CNO⁻). Carbon has 4 valence electrons, nitrogen has 5, oxygen has 6, and the negative charge adds 1 extra electron. So, total valence electrons = 4 + 5 + 6 + 1 = 16 electrons.
Step 2: Arrange the atoms in a plausible structure. Typically, carbon is central in CNO⁻, bonded to nitrogen, which is bonded to oxygen. This gives a linear or nearly linear arrangement: C - N - O.
Step 3: Draw bonds between the atoms and distribute electrons to satisfy the octet rule as much as possible. Start by placing single bonds between C-N and N-O, then add lone pairs to complete octets, adjusting bond orders (single, double, triple) to use all 16 electrons and minimize formal charges.
Step 4: Calculate formal charges for each atom using the formula: Formal charge = (Valence electrons) - (Nonbonding electrons) - 1/2(Bonding electrons). The best Lewis structure has the smallest formal charges and places the negative charge on the most electronegative atom, which is oxygen in this case.
Step 5: Compare the given options with your calculated structure. The correct Lewis structure will have a triple bond between C and N, a single bond between N and O, no lone pairs on C, one lone pair on N, three lone pairs on O, and the negative charge localized on oxygen.
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