Draw the Lewis dot structure for acetic acid (C2H4O2).

Draw the Lewis dot structure for acetic acid (C2H4O2). Include any lone pairs.

The Correct Answer and Explanation is:

Lewis Dot Structure of Acetic Acid (C₂H₄O₂):

Acetic acid has the molecular formula C₂H₄O₂, and its structure includes a carboxylic acid functional group. Here’s the correct Lewis structure:

       O
       ||
H – C – C – O – H
       |
       H

Step-by-Step Lewis Structure:

1. Count total valence electrons:
   • Carbon (C): 4 valence electrons × 2 = 8
   • Hydrogen (H): 1 valence electron × 4 = 4
   • Oxygen (O): 6 valence electrons × 2 = 12
   • Total = 8 + 4 + 12 = 24 valence electrons
2. Determine the skeletal structure:
   • Acetic acid has a methyl group (CH₃) connected to a carboxylic acid group (COOH).
   • This gives us: CH₃–COOH
3. Assign single bonds first:
   • Connect the atoms:
     H–C–C–O–H, with a double bond between the second carbon and one oxygen.
4. Distribute remaining electrons:
   • Complete octets around oxygen atoms.
   • Place lone pairs on oxygen atoms:
     • The double-bonded oxygen has two lone pairs.
     • The single-bonded OH oxygen has two lone pairs as well.
5. Check octets and valence electrons:
   • All atoms satisfy the octet rule (except hydrogen, which only needs 2 electrons).
   • Total electron count = 24

Final Lewis Structure (with lone pairs):

        ..
     :O:
      ||
H–C–C–O–H
    |   ..
    H   :

• The first carbon is bonded to three hydrogens and one carbon.
• The second carbon is bonded to one carbon, one double-bonded oxygen (with 2 lone pairs), and one single-bonded OH group (O with 2 lone pairs and H).

Explanation

The Lewis structure of acetic acid (C₂H₄O₂) illustrates the bonding and arrangement of atoms and electrons in the molecule. Acetic acid consists of two carbon atoms, four hydrogen atoms, and two oxygen atoms. Understanding the molecular structure is crucial for predicting reactivity, polarity, and physical properties.

The molecule is built around a carboxylic acid group (-COOH), a defining functional group in organic chemistry. One carbon is part of a methyl group (CH₃), bonded to three hydrogen atoms and the second carbon. The second carbon, known as the carboxylic carbon, is double bonded to one oxygen atom (a carbonyl oxygen) and single bonded to a hydroxyl group (-OH).

Carbon atoms follow the octet rule, forming four bonds. Oxygen atoms form two bonds and have two lone pairs. In this molecule, one oxygen is double bonded to the carbon (with two lone pairs), while the other is single bonded to both carbon and hydrogen and has two lone pairs as well.

Each hydrogen makes a single bond (1 valence electron) and completes its duet. All atoms in this structure have full outer shells—carbons and oxygens have octets, and hydrogens have two electrons.

This structure reflects the acidic nature of acetic acid—the proton (H⁺) from the hydroxyl group can dissociate, making acetic acid weakly acidic. The double bond between carbon and oxygen creates partial charges that stabilize the conjugate base after deprotonation.

Understanding the Lewis structure helps in predicting how acetic acid will interact in chemical reactions—especially in acid-base chemistry and organic synthesis.