Sigma and Pi Bonds
Bonding Worksheet
Draw a labelled diagram representing a double bond between two carbon atoms.
Answer
Describe the structure of a sigma bond between two carbon atoms.
Answer
- The overlap of two orbitals so that the electron density is localised between the two nuclei.
- The orbitals involved are either s-orbitals, or sp hybrid orbitals.
Describe the structure of a pi bond between two carbon atoms.
Answer
- The overlap of two p-orbitals so that they overlap laterally.
- The electron density is found above and below the mid-point between the two nuclei.
The C-C bond in ethane has a bond dissociation enthalpy of 348 kJ mol-1, whereas the C=C bond in ethene has a bond dissociation enthalpy of 612 kJ mol-1. Explain why the double bond is not twice as strong as a single bond.
Answer
- Single bonds are made of only a sigma bond, whereas double bonds are made of a sigma bond and a pi bond.
- Pi bonds are weaker than sigma bonds.
- This is because the electrons in a pi bond are found above and below the internuclear axis.
A larger bond dissociation enthalpy would suggest that more energy is required to break the bond, which in turn suggests that molecules with C=C are less reactive than molecules with C-C. Explain why this is not the case.
Answer
- The pi bond electrons are found above and below the internuclear axis.
- This means that they are held less strongly than sigma bond electrons.
- The pi bond can break without the sigma bond breaking.