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Chapter 8: Problem 52

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) \(\mathrm{SO}_{2}\), (b) \(\mathrm{SO}_{3}\) (c) \(\mathrm{SO}_{3}^{2-}\). (d) Arrange these molecules/ions in order of increasing \(\mathrm{S}-\mathrm{O}\) bond length.

Short Answer

Expert verified
The Lewis structures, oxidation numbers, and formal charges for the given molecules or ions are: (a) SO2: O=S=O, oxidation numbers: S(+4), O(-2); formal charges: S(0), O(0). (b) SO3: O=S(=O)(=O), oxidation numbers: S(+6), O(-2); formal charges: S(0), O(0). (c) SO3 2-: O-S(-O)(-O), oxidation numbers: S(+4), O(-2); formal charges: S(+1), O(-1). In order of increasing S-O bond length: SO3, SO2, SO3 2-.

Step by step solution

01

(a) SO2 Lewis Structure

1. Count the valence electrons: Sulfur has 6 valence electrons, and Oxygen has 6 valence electrons each. So, the total number of valence electrons for SO2 is 18. 2. Place the least electronegative atom (S) in the center and connect it with the other atoms (O) with single bonds. 3. Complete the octet of each surrounding atom (O) by adding lone pairs of electrons. 4. Check if the central atom (S) has an octet. If not, form a double bond by moving a lone pair from the surrounding atom (O) to form a bonding pair with the central atom (S). The Lewis structure of SO2 is: O=S=O
02

SO2 Oxidation Numbers and Formal Charges

Oxidation numbers: S: +4 (it has 4 electrons less than the neutral atom) O: -2 (each oxygen atom has 2 electrons more than the neutral atom) Formal charges: For S: Formal charge = Valence electrons - Non-bonding electrons - (1/2 * Bonding electrons) = 6 - 0 - (1/2 * 8) = 0 For each O: Formal charge = 6 - 4 - (1/2 * 4) = 0
03

(b) SO3 Lewis Structure

1. Count the valence electrons: Sulfur has 6 valence electrons, and Oxygen has 6 valence electrons each. So, the total number of valence electrons for SO3 is 24. 2. Place the least electronegative atom (S) in the center and connect it with the other atoms (O) with single bonds. 3. Complete the octet of each surrounding atom (O) by adding lone pairs of electrons. 4. Check if the central atom (S) has an octet. If not, form double bonds by moving a lone pair from the surrounding atom (O) to form a bonding pair with the central atom (S) until the central atom has an octet. Once complete, SO3 will have one double bond with each of the three oxygen atoms.
04

SO3 Oxidation Numbers and Formal Charges

Oxidation numbers: S: +6 (it has 6 electrons less than the neutral atom) O: -2 (each oxygen atom has 2 electrons more than the neutral atom) Formal charges: For S: Formal charge = 6 - 0 - (1/2 * 12) = 0 For each O: Formal charge = 6 - 4 - (1/2 * 4) = 0
05

(c) SO3 2- Lewis Structure

1. Count the valence electrons: Sulfur has 6 valence electrons, Oxygen has 6 valence electrons each, and there are 2 additional electrons from the 2- charge. The total number of valence electrons for SO3 2- is 26. 2. Place the least electronegative atom (S) in the center and connect it with the other atoms (O) with single bonds. 3. Complete the octet of each surrounding atom (O) by adding lone pairs of electrons. 4. Check if the central atom (S) has an octet. It does, so there are no additional steps. In this case, all sulfur-oxygen bonds are single bonds.
06

SO3 2- Oxidation Numbers and Formal Charges

Oxidation numbers: S: +4 (it has 4 electrons less than the neutral atom) O: -2 (each oxygen atom has 2 electrons more than the neutral atom) Formal charges: For S: Formal charge = 6 - 2 - (1/2 * 6) = +1 For each O: Formal charge = 6 - 6 - (1/2 * 2) = -1 Note: The overall charge of the ion is -1 * 3 + 1 = -2, which is consistent with the given charge.
07

(d) Arrange Molecules/Ions in Order of Increasing S-O Bond Length

S-O bond length increases with decreasing bond order. Bond order can be determined by the number of bonds between the atoms. The Lewis structures show the bond orders. SO2 has an average bond order of 3/2 (since there is one double bond and one single bond), SO3 has a bond order of 2 (all double bonds), and SO3 2- has a bond order of 1 (all single bonds). In order of increasing S-O bond length: 1. SO3 (highest bond order, which means the shortest bond length) 2. SO2 (intermediate bond order and bond length) 3. SO3 2- (lowest bond order, which means the longest bond length)

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Most popular questions from this chapter

Draw Lewis structures for the following: $(\mathbf{a}) \mathrm{CH}_{2} \mathrm{Cl}_{2},(\mathbf{b}) \mathrm{ClCN},\( (c) \)\mathrm{AsF}_{5}$ (d) \(\mathrm{CH}_{2} \mathrm{O}\) (C the central atom), (e) \(\mathrm{OF}_{2}\) (f) \(\mathrm{NO}_{3}^{-}\).

Using Lewis symbols and Lewis structures, diagram the formation of \(\mathrm{BF}_{3}\) from \(\mathrm{B}\) and \(\mathrm{F}\) atoms, showing valence- shell electrons. (a) How many valence electrons does B have initially? (b) How many bonds F has to make in order to achieve an octet? (c) How many valence electrons surround the \(\mathrm{B}\) in the \(\mathrm{BF}_{3}\) molecule? (d) How many valence electrons surround each \(\mathrm{F}\) in the \(\mathrm{BF}_{3}\) molecule? (e) Does \(\mathrm{BF}_{3}\) obey the octet rule?

A carbene is a compound that has a carbon bonded to two atoms and a lone pair remaining on the carbon. Many carbenes are very reactive. (a) Draw the Lewis structure for the simplest carbene, \(\mathrm{H}_{2} \mathrm{C}\). (b) Predict the length of the carbon-carbon bond you would expect if two $\mathrm{H}_{2} \mathrm{C}$ molecules reacted with each other by a combination reaction.

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