Draw the Lewis structure for the acetate ion, CH3CO2^-, including any important resonance structures. label each atom with its formal charge.
The Correct Answer and Explanation is :
To draw the Lewis structure for the acetate ion (CH₃CO₂⁻) and its resonance forms, we’ll start by arranging the atoms and electrons, and then label each atom with its formal charge.
Lewis Structure of Acetate Ion
- Arrangement of Atoms:
- Carbon (C) is the central atom connected to three hydrogen (H) atoms and an oxygen (O) atom in a methyl group (CH₃).
- The second carbon atom is double bonded to one oxygen atom and single bonded to another oxygen atom, which carries the extra negative charge.
- Electron Distribution:
- The total number of valence electrons for the acetate ion = 4 (C) + 3(1H) + 4(O) + 4(O) + 1 (extra electron from the charge) = 24 electrons.
- In CH₃, each hydrogen is bonded to carbon, using 6 electrons.
- The central carbon is bonded to another carbon, using 2 more electrons (8 used so far).
- One oxygen is double bonded to carbon (using 4 more electrons, 12 total), and the other oxygen is single bonded to carbon and has three lone pairs (8 more electrons, 20 total).
- The remaining electrons (4) are placed as lone pairs on the doubly bonded oxygen.
- Formal Charges:
- On the CH₃ group, all atoms are neutral.
- On the second carbon, no formal charge.
- The oxygen in the double bond without the negative charge is neutral, as it shares two bonding pairs with carbon.
- The singly bonded oxygen, with three lone pairs and a single bond, carries a -1 charge due to the extra pair of electrons compared to its normal valence.
- Resonance Structures:
- Resonance occurs by shifting one of the lone pairs on the singly bonded oxygen to form a double bond with the central carbon, while the double bond between the central carbon and the other oxygen converts to a single bond, placing a lone pair on that oxygen.
- This shift creates an equivalent structure where the negative charge is now located on the other oxygen.
Explanation
Resonance structures are a way to represent molecules where the bonding cannot be expressed by a single Lewis structure. In acetate, resonance allows the ion to have more stability by delocalizing the negative charge across two oxygen atoms. This delocalization reduces the electron density on any one atom, distributing it more evenly across the molecule, which enhances stability. Both resonance forms contribute equally to the real, hybrid structure of the molecule, which is an average of the resonance forms. This concept is crucial in understanding the chemical behavior and reactivity of acetate in various chemical reactions, particularly in organic chemistry where it acts as a common nucleophile.
Now, I’ll generate an image depicting the Lewis structures, including resonance forms and formal charges.
Here is the illustration showing the Lewis structure of the acetate ion (CH₃CO₂⁻), including its resonance forms and the formal charges on each atom. This visual representation should help clarify how the electron distribution and formal charges are arranged in this ion.
