When two carbon atoms form a double bond, such as in ethene (C2H4), specific types of covalent bonds are involved. Which of the following statements correctly describes the nature of these bonds?
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The answer
Correct answer: B. A carbon-carbon double bond is composed of one sigma (σ) bond and one pi (π) bond, where the pi bond prevents free rotation.
Tested concept: Sigma and pi bonds
Explanation
A carbon-carbon double bond is always comprised of one sigma (σ) bond and one pi (π) bond. The sigma bond is formed by the direct, head-on overlap of atomic orbitals, allowing for free rotation around the bond axis. The pi bond is formed by the lateral (side-by-side) overlap of unhybridized p orbitals, which restricts rotation around the bond axis, contributing to the planar geometry of molecules like ethene. Therefore, the statement that a carbon-carbon double bond is composed of one sigma (σ) bond and one pi (π) bond, where the pi bond prevents free rotation, is correct. The other options contain inaccuracies regarding the number and type of bonds or their formation and properties.
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