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Ch.9 - Chemical Bonding I: The Lewis Model
All textbooksTro 4th EditionCh.9 - Chemical Bonding I: The Lewis ModelProblem 79a
Chapter 9, Problem 79a

Order these compounds in order of increasing carbon–carbon bond strength: HCCH, H2CCH2, H3CCH3.

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Identify the types of carbon-carbon bonds in each compound: HCCH has a triple bond, H_2CCH_2 has a double bond, and H_3CCH_3 has a single bond.
Recall that bond strength generally increases with the number of shared electron pairs: single bonds are weaker than double bonds, which are weaker than triple bonds.
Order the compounds based on the bond types: single bond (H_3CCH_3), double bond (H_2CCH_2), and triple bond (HCCH).
Conclude that the order of increasing carbon-carbon bond strength is: H_3CCH_3, H_2CCH_2, HCCH.
Review the concept that bond strength is related to bond order, with higher bond orders indicating stronger bonds.

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Key Concepts

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

Carbon-Carbon Bond Types

Carbon-carbon bonds can be classified into three types: single (sigma), double (one sigma and one pi), and triple bonds (one sigma and two pi). The strength of these bonds increases with the number of shared electron pairs; thus, triple bonds are stronger than double bonds, which are stronger than single bonds.
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Bonding Types

Hybridization

Hybridization refers to the mixing of atomic orbitals to form new hybrid orbitals that can form bonds. In the context of carbon, sp hybridization (as in HCCH) leads to stronger bonds due to the linear arrangement and greater s-character, while sp² (as in H2CCH2) and sp³ (as in H3CCH3) have different bond strengths due to their respective geometries and electron distributions.
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Steric Effects

Steric effects arise from the spatial arrangement of atoms in a molecule, influencing bond strength and stability. In larger alkyl groups, such as in H3CCH3, increased steric hindrance can weaken the carbon-carbon bond compared to less hindered structures like HCCH, where the linear arrangement allows for closer approach of the bonding orbitals.
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Related Practice
Textbook Question

Write Lewis structures for each molecule or ion. Use expanded octets as necessary. a. PF5

Textbook Question

Write Lewis structures for each molecule or ion. Use expanded octets as necessary. b. AsF6-

Textbook Question

Order these compounds in order of decreasing carbon–carbon bond length: HCCH, H2CCH2, H3CCH3.

Textbook Question

Which of the two compounds, H2NNH2 and HNNH, has the strongest nitrogen-nitrogen bond, and which has the shorter nitrogen-nitrogen bond.

Textbook Question

Hydrogenation reactions are used to add hydrogen across double bonds in hydrocarbons and other organic compounds. Use average bond energies to calculate ΔHrxn for the hydrogenation reaction. H2C=CH2(g) + H2(g) → H3C–CH3(g)

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