Part III: Formal Charges and Planar Molecules Draw three different Lewis structures for the cyanate ion, OCN, using the skeleton structures below: L indicuted Indicate the formal charge for each atom in each formula as Circle the most plausible Lewis structure based on the formal charges. OCN OCN OCN The molecular geometry of OCN and it bond angle is 2 For the following molecule and polyatomic ion, Draw the Lewis Structure (including resonance structures if applicable) where the central atom obeys the octet rule, ii. Determine and indicate the format charge for each atom in the molecule or polyatomic ion, Rearrange electrons to minimize the formal charges, so the central atom has an expanded octet if necessary. SO, Lewis structure where S obeys the octet rule, corrected Lewis structure charges showing formal showing formal charges The molecular geometry of SO, is it bond angles are and b chlorate ion, CIO, Lewis structure where Cl obeys the octet rule, corrected Lewis structure showing formal charges showing formal charges
The Correct Answer and Explanation is :
Part III: Formal Charges and Planar Molecules
1. Cyanate Ion (OCN⁻)
The cyanate ion has the formula OCN⁻. It consists of one oxygen (O) atom, one carbon (C) atom, and one nitrogen (N) atom, with an overall negative charge.
Possible Lewis Structures for OCN⁻
To draw three different Lewis structures for cyanate (OCN⁻), we will place each atom according to a reasonable skeleton and then distribute electrons.
Structure 1:
- Carbon in the center.
- A single bond to oxygen and nitrogen.
- O has a lone pair (one lone pair on oxygen).
- Nitrogen has one lone pair.
Formal charges for Structure 1:
- Oxygen (O) has a formal charge of 0.
- Carbon (C) has a formal charge of +1.
- Nitrogen (N) has a formal charge of -1.
- Total formal charge = -1 (which matches the ion’s charge).
Structure 2:
- Carbon in the center.
- Double bond to oxygen and single bond to nitrogen.
- Oxygen has two lone pairs, and nitrogen has two lone pairs.
Formal charges for Structure 2:
- Oxygen (O) has a formal charge of 0.
- Carbon (C) has a formal charge of 0.
- Nitrogen (N) has a formal charge of -1.
- Total formal charge = -1 (matching the ion’s charge).
Structure 3:
- Carbon in the center.
- Double bond to nitrogen and single bond to oxygen.
- Oxygen has lone pairs, and nitrogen has lone pairs.
Formal charges for Structure 3:
- Oxygen (O) has a formal charge of -1.
- Carbon (C) has a formal charge of 0.
- Nitrogen (N) has a formal charge of +1.
- Total formal charge = -1 (matching the ion’s charge).
The most plausible structure is Structure 2, where oxygen is double-bonded to carbon, and nitrogen is single-bonded to carbon. This structure minimizes formal charges on each atom, with oxygen having no formal charge and nitrogen having a formal charge of -1.
2. Sulfur Dioxide (SO₂)
For SO₂, sulfur (S) is the central atom, and oxygen (O) atoms are bonded to sulfur.
Lewis Structure for SO₂:
- The structure typically has sulfur in the center, with double bonds to two oxygen atoms.
- Each oxygen atom has two lone pairs, and sulfur has two lone pairs.
- The formal charges will be minimized when the oxygen atoms each have a formal charge of 0, and sulfur has a formal charge of 0 as well.
Formal charges:
- Oxygen (O) atoms have a formal charge of 0.
- Sulfur (S) has a formal charge of 0.
Since there are no formal charges on any atom, this is the most stable and plausible structure.
3. Chlorate Ion (ClO₃⁻)
The chlorate ion (ClO₃⁻) consists of chlorine (Cl) as the central atom and three oxygen atoms bonded to it. There is an extra electron, giving it an overall negative charge.
Lewis Structure for ClO₃⁻:
- Chlorine will be in the center, bonded to three oxygen atoms.
- Two of the oxygen atoms will have double bonds to chlorine, and one will have a single bond with chlorine.
- The oxygen with the single bond will have a formal negative charge, while chlorine will have a formal positive charge.
Formal charges:
- Two oxygen atoms with double bonds to chlorine will have a formal charge of 0.
- The oxygen with the single bond will have a formal charge of -1.
- Chlorine will have a formal charge of +1.
To minimize formal charges, we can have one oxygen atom with a single bond to chlorine, and the others double-bonded to chlorine. This will help distribute the formal charges more evenly and match the overall negative charge.
Molecular Geometry:
- OCN⁻: The geometry is linear with a bond angle of approximately 180°.
- SO₂: The geometry is bent (V-shaped) with bond angles of approximately 120°.
- ClO₃⁻: The geometry is trigonal planar with bond angles of approximately 120°.
In conclusion, when constructing Lewis structures, it is essential to minimize formal charges and adhere to the octet rule, unless an expanded octet is required. These structures allow for a better understanding of bonding and charge distribution in molecules.