Ch.9 - Molecular Geometry and Bonding Theories

Brown - Chemistry: The Central Science 15th Edition

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Brown 15th Edition

Ch.9 - Molecular Geometry and Bonding Theories

Problem 91e

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.

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.

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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Bond Angles

Related Practice

Textbook Question

An AB3 molecule is described as having a trigonal-bipyramidal electron-domain geometry b. Based on the information given, which of the following is the molecular geometry of the molecule:

i. trigonal planar

ii. trigonal pyramidal

iii. T-shaped or

iv. tetrahedral?

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Textbook Question

Fill in the blank spaces in the following chart. If the molecule column is blank, find an example that fulfills the conditions of the rest of the row. Molecule Electron-Domain Hybridization Dipole Geometry of Central Atom Moment? Yes or No CO2 sp³ Yes sp³ No Trigonal planar No SF₄ Octahedral No sp² Yes Trigonal bipyramidal No XeF₂

582

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Textbook Question

An AB5 molecule adopts the geometry shown here. b. What is the electron-domain geometry for the molecule?

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Textbook Question

An AB5 molecule adopts the geometry shown here.

c. Suppose the B atoms are halogen atoms. Of which group in the periodic table is atom A a member:

i. group 5A

ii. group 6A

iii. group 7A

iv. group 8A, or

v. is more information needed?

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Textbook Question

The O—H bond lengths in the water molecule (H2O) are 0.96 Å, and the H—O—H angle is 104.5°. The overall dipole moment of the water molecule is 1.85 D. b. Calculate the magnitude of the bond dipole of the O─H bonds. (Note: You will need to use vector addition to do this.)

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