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Ch.9 - Molecular Geometry and Bonding Theories
Chapter 9, Problem 91e

The lactic acid molecule, CH3CH(OH)COOH, gives sour milk its unpleasant, sour taste. e. What are the approximate bond angles around each carbon atom in the molecule?

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Identify the hybridization of each carbon atom in the lactic acid molecule.
For the first carbon atom (CH3), recognize that it is sp3 hybridized, which typically results in bond angles of approximately 109.5°.
For the second carbon atom (CH(OH)), determine that it is also sp3 hybridized, leading to bond angles of approximately 109.5°.
For the third carbon atom (COOH), note that it is sp2 hybridized, which generally results in bond angles of approximately 120°.
Summarize the bond angles: around the first and second carbon atoms, the angles are approximately 109.5°, and around the third carbon atom, the angles are approximately 120°.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. The shape of a molecule is determined by the number of bonding pairs and lone pairs of electrons around the central atom, which influences the bond angles. In the case of lactic acid, understanding its geometry helps predict the bond angles around each carbon atom.
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Hybridization

Hybridization is the concept of mixing atomic orbitals to form new hybrid orbitals that can accommodate bonding. In lactic acid, the carbon atoms undergo sp3 hybridization, which results in tetrahedral geometry. This hybridization explains the bond angles, typically around 109.5 degrees for sp3 hybridized carbons.
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Bond Angles

Bond angles are the angles formed between two bonds that share a common atom, crucial for understanding molecular shape. In lactic acid, the bond angles around the carbon atoms vary due to the presence of different substituents and hybridization. For sp3 hybridized carbons, the ideal bond angle is approximately 109.5 degrees, but steric effects from adjacent groups can slightly alter this angle.
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