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Ch.7 - Covalent Bonding and Electron-Dot Structures
Chapter 7, Problem 2

Which molecule has the shortest carbon–oxygen bond? (LO 7.3, 7.9) (a) CH3OH (b) CO (c) CO2 (d) HCOOH

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Identify the type of carbon-oxygen bonds present in each molecule. CH3OH has a single C-O bond, CO has a triple C-O bond, CO2 has two double C-O bonds, and HCOOH has both a single and a double C-O bond.
Recall that multiple bonds (double and triple bonds) are generally shorter than single bonds due to the increased electron density between the atoms.
Compare the types of bonds: A triple bond is shorter than a double bond, which in turn is shorter than a single bond.
Determine which molecule has the highest order of bond between carbon and oxygen. In this case, CO has a triple bond.
Conclude that the molecule with the highest order of bond (CO, with a triple bond) will have the shortest carbon-oxygen bond.

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Key Concepts

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

Bond Length

Bond length refers to the distance between the nuclei of two bonded atoms. In general, shorter bonds indicate stronger interactions between the atoms due to greater overlap of their atomic orbitals. Factors such as the type of bond (single, double, or triple) and the electronegativity of the atoms involved can influence bond length.
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Average Bond Order

Types of Bonds

The type of bond between atoms significantly affects bond length. Carbon-oxygen bonds can be single (C–O), double (C=O), or even triple (C≡O). Double and triple bonds are typically shorter than single bonds due to increased electron sharing, which pulls the atoms closer together.
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Bonding Types

Molecular Geometry

Molecular geometry describes the three-dimensional arrangement of atoms in a molecule. The shape can influence bond lengths and angles due to steric effects and electron repulsion. Understanding the geometry of the molecules in the question helps predict which carbon-oxygen bond might be the shortest based on their structural characteristics.
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Molecular Geometry with Two Electron Groups