Lengths of Bonds

[Tatiana R Dis 3E]

If a molecule such as C2H2 has one triple bond between the two Carbons and single bonds with the two Hydrogens. Is the triple bond shorter than the single bonds? I was confused by resonance, but there can only be one possible Lewis structure for C2H2 so there isn't resonance, right?

[Christian Fulinara 3H]

A triple bond would be shorter than a single bond "because the additional bonding electrons attract the nuclei more strongly and pull the atoms closer together" (96). There should be only one structure for C2H2 because the there could only be one triple bond between the carbons. If there was a double bond, there would be a possibility to have cis- or trans- resonance structures, but that is not the case.

[Sarah_Stay_1D]

If a molecule such as C2H2 has one triple bond between the two Carbons and single bonds with the two Hydrogens. Is the triple bond shorter than the single bonds? I was confused by resonance, but there can only be one possible Lewis structure for C2H2 so there isn't resonance, right?

Triple bonds are always shorter than single bonds. In the case of C2H2, you are right there is only one possible lewis structure. Since there is only one possible lewis structure C2H2 does not have resonance. A molecule has resonance if more than one lewis structure can be drawn for that molecule. For molecules with resonance, each lewis structure individually does not accurately depict the structure of the molecule. The actual structure of the molecule is better represented by the average of all the resonance structures.