Acetic acid has the following Lewis structure, using the VSEPR model, predict the

Acetic acid has the following Lewis structure, using the VSEPR model, predict the: A. Electron-Domain Geometry B. Molecular Geometry C. bond angles at each central atom H ::O:: H-C-C-O-H H

The Correct Answer and Explanation is:¹

1. ↩︎

Certainly! Here’s a breakdown of acetic acid’s geometry using VSEPR theory:

A. Electron-Domain Geometry

1. First Carbon (methyl group CH₃): This carbon is bonded to three hydrogen atoms and one carbon atom, giving it four electron domains, which leads to a tetrahedral electron-domain geometry.
2. Second Carbon (carboxyl group): This central carbon is bonded to one oxygen atom via a double bond, one oxygen atom via a single bond, and one carbon atom. It also has three electron domains, resulting in a trigonal planar electron-domain geometry.
3. Hydroxyl Oxygen (OH group): This oxygen atom is bonded to one hydrogen atom and one carbon atom, plus it has two lone pairs, for a total of four electron domains, indicating a tetrahedral electron-domain geometry.

B. Molecular Geometry

1. First Carbon (CH₃): Since all four domains are bonding pairs, the molecular geometry remains tetrahedral.
2. Second Carbon (central C of COOH): All three domains are bonding pairs with no lone pairs, so its molecular geometry is trigonal planar.
3. Hydroxyl Oxygen (OH): With two bonding pairs and two lone pairs, the molecular shape becomes bent.

C. Bond Angles

1. First Carbon (CH₃): The bond angles are approximately 109.5 degrees, typical of tetrahedral geometry.
2. Second Carbon (COOH group): This atom exhibits 120-degree bond angles, consistent with a trigonal planar structure.
3. Hydroxyl Oxygen (OH): The bond angle is about 104.5 degrees, similar to that in water, due to repulsion from the lone pairs.

Explanation (300 words) Acetic acid (CH₃COOH) contains two central atoms—one in the methyl group (CH₃) and one in the carboxyl group (COOH). Using the Valence Shell Electron Pair Repulsion (VSEPR) model, we evaluate each center independently to determine geometries and angles.

The methyl carbon is surrounded by four sigma bonds—three to hydrogen atoms and one to the adjacent carbon. VSEPR predicts that four bonding domains arrange themselves to minimize repulsion by adopting a tetrahedral geometry with bond angles of approximately 109.5 degrees.

The carbon in the carboxyl group is unique. It forms a double bond with one oxygen, a single bond with another oxygen (part of the hydroxyl group), and one bond with the methyl carbon. These three regions of electron density form a planar triangle, leading to a trigonal planar electron-domain and molecular geometry, with bond angles close to 120 degrees. There are no lone pairs on this carbon, so the angle remains undistorted.

The hydroxyl oxygen is bonded to the carbon and to a hydrogen atom. Two non-bonding electron pairs are present as well, totaling four electron domains. The lone pairs repel more strongly than bonding pairs, compressing the angle between bonds. This results in a bent molecular shape, similar to water, with bond angles around 104.5 degrees.

Thus, VSEPR theory helps rationalize the specific 3D shape of each center in the molecule, revealing that although acetic acid is small, it incorporates a variety of molecular geometries within its structure.