Which statement correctly defines a sigma bond and a pi bond?

• A. Sigma bond is formed by end-to-end overlap along the bond axis; Pi bond is formed by sideways overlap above and below the bond axis
• B. Pi bond is formed by end-to-end overlap along the bond axis; Sigma bond is formed by sideways overlap above and below the bond axis
• C. Sigma bond is formed by resonance; Pi bond is formed by electronegativity differences
• D. Sigma bond is present only in triple bonds; Pi bond is present only in double bonds

Answer: (A)

Understanding how sigma and pi bonds form helps explain why this pairing is correct. A sigma bond arises from end-to-end overlap of orbitals along the line between the two nuclei, so electron density is concentrated directly along that bond axis. A pi bond comes from sideways overlap of adjacent p orbitals, placing electron density above and below the bond axis rather than along it. This is why a single bond is typically a sigma bond, and in double and triple bonds you have one sigma bond plus one or two pi bonds. The statement accurately captures this distinction: sigma from end-to-end overlap along the axis, pi from sideways overlap above and below the axis. The other ideas—that pi bonds come from resonance or electronegativity differences, or that pi bonds exist only in certain bond orders—don’t reflect how orbital overlap actually builds covalent bonds.