Question

Write Lewis structures that obey the octet rule for each of the following, and assign oxidation numbers and formal charges to each atom: $(\mathbf{a}) \mathrm{OCS},(\mathbf{b}) \mathrm{SOCl}_{2}(\mathrm{~S}$ is the central atom), (c) ${\mathrm{BrO}}_3^{-}$, (d) ${\mathrm{HClO}}_2(\mathrm{H}$ is bonded to $\mathrm{O})$.

Short answer

For the given molecules and ions, the Lewis structures that obey the octet rule are: 1. OCS: O=C=S with oxidation numbers O(-2), C(+4), and S(-2), and formal charges O(0), C(0), and S(0). 2. SOCl₂: O=S(Cl)₂ with oxidation numbers O(-2), S(+4), and Cl(-1) for each Cl, and formal charges O(0), S(0), and Cl(0) for each Cl. 3. BrO₃⁻: O--Br(--O)₂ with oxidation numbers O(-2) for each O, and Br(+5), and formal charges O(0) for each O, and Br(-1). 4. HClO₂: H--O--Cl(--O)₂ with oxidation numbers H(+1), O(-2), Cl(+3), and O(-2) for each O, and formal charges H(0), O(0), Cl(+1), and O(0) for each O.

Step-by-step solution

A. Drawing Lewis structures

To draw the Lewis structures, first, write the skeletal structure for each molecule, identify the total number of valence electrons available, and then distribute them around each atom to follow the octet rule. 1. OCS Skeletal structure: O=C=S Valence electrons: O (6) + C (4) + S (6) = 16 2. SOCl₂ (S is the central atom) Skeletal structure: O=S(Cl)₂ Valence electrons: S (6) + O (6) + 2 * Cl (7) = 26 3. BrO₃⁻ (with a negative charge) Skeletal structure: O--Br(--O)₂ Valence electrons: Br (7) + 3 * O (6) + 1 (from negative charge) = 26 4. HClO₂ (H is bonded to O) Skeletal structure: H--O--Cl(--O)₂ Valence electrons: H (1) + O (6) + Cl (7) + 2 * O (6) = 26

B. Assign oxidation numbers

To assign oxidation numbers, consider each bond as if the electron pairs were completely transferred to the more electronegative atom. 1. OCS O (Ox#: -2), C (Ox#: +4), S (Ox#: -2) 2. SOCl₂ O (Ox#: -2), S (Ox#: +4), Cl (Ox#: -1) for each Cl 3. BrO₃⁻ O (Ox#: -2) for each O, Br (Ox#: +5) 4. HClO₂ H (Ox#: +1), O (Ox#: -2), Cl (Ox#: +3), O (Ox#: -2) for each O

C. Calculate formal charges

To calculate formal charges, compare the number of valence electrons in the atom when not bonded to the number of electrons assigned to the atom in the molecule/ion. Formal Charge (FC) = Valence electrons - Nonbonding electrons - ½ * bonding electrons. 1. OCS Formal charges: O (FC: 0), C (FC: 0), S (FC: 0) 2. SOCl₂ Formal charges: O (FC: 0), S (FC: 0), Cl (FC: 0) for each Cl 3. BrO₃⁻ Formal charges: O (FC: 0) for each O, Br (FC: -1) 4. HClO₂ Formal charges: H (FC: 0), O (FC: 0), Cl (FC: +1), O (FC: 0) for each O. These Lewis structures with the assigned oxidation numbers and formal charges should obey the octet rule when drawn correctly.