1. Count the valence electrons:
* Carbon (C): 4 valence electrons x 2 = 8
* Hydrogen (H): 1 valence electron x 3 = 3
* Oxygen (O): 6 valence electrons x 2 = 12
* Charge (-1): +1
Total valence electrons: 8 + 3 + 12 + 1 = 24
2. Connect the atoms:
* The two carbons form a single bond.
* Each carbon has three hydrogen atoms attached to it (methyl group).
* One oxygen atom is double-bonded to a carbon.
* The other oxygen atom is single-bonded to the same carbon.
3. Distribute the remaining electrons:
* Start by completing the octets of the outer oxygen atoms (the one with the double bond and the one with the single bond). Each needs 6 more electrons.
* The central carbon with the double bond already has an octet.
* The central carbon with the single bond only has 6 electrons. To complete its octet, it needs 2 more electrons. You can move one of the lone pairs from the negatively charged oxygen to form a double bond between the carbon and oxygen.
4. Indicate the charge:
* Since the acetate ion has a negative charge, place square brackets around the structure and write the -1 charge outside the brackets.
Final Lewis Structure:
```
H
|
H - C - C = O
| ||
H O⁻
|
H
[CH₃COO]⁻
```
Key points:
* The double bond can be placed on either of the oxygen atoms. Both are equivalent resonance structures.
* The negative charge is delocalized between the two oxygen atoms.
* The Lewis structure helps us visualize the bonding and electron distribution in the acetate ion.
