Draw the molecular orbital diagram for the molecules of ethene (CH2=CH2) and ethyne (CH≡CH)
The Correct Answer and Explanation is:
Molecular Orbital Diagram for Ethene (C₂H₄) and Ethyne (C₂H₂)
Ethene (C₂H₄):
Ethene is a molecule with a double bond between two carbon atoms. Each carbon in ethene is sp² hybridized, and the molecule has a trigonal planar geometry. For the molecular orbital diagram:
- Bonding and Antibonding Orbitals: The bonding and antibonding molecular orbitals for ethene come from the overlap of the atomic orbitals from each carbon and hydrogen.
- The carbon-carbon sigma (σ) bond arises from the head-on overlap of sp² hybrid orbitals.
- The π bond comes from the sideways overlap of unhybridized p orbitals from the two carbon atoms.
- The hydrogen atoms contribute to the bonding orbitals through the overlap of their 1s orbitals with the carbon sp² hybrid orbitals.
- Orbital Filling:
- The σ and σ* orbitals (for the carbon-carbon bond) are filled first, followed by the π bonding and π* antibonding orbitals.
- The electrons fill the molecular orbitals based on the Pauli Exclusion Principle and Hund’s Rule.
In total, the bonding in ethene involves one σ bond, one π bond, and the interactions with the hydrogens contribute to the bonding network.
Ethyne (C₂H₂):
Ethyne has a triple bond between two carbon atoms. Each carbon in ethyne is sp hybridized, resulting in a linear geometry. In the molecular orbital diagram:
- Bonding and Antibonding Orbitals:
- The carbon-carbon sigma (σ) bond comes from the overlap of sp hybrid orbitals.
- Two π bonds form from the sideways overlap of two p orbitals on each carbon atom.
- Orbital Filling:
- The σ bonding and antibonding orbitals fill first, followed by the two π bonding and π* antibonding orbitals.
- The two remaining electrons will be placed in the lowest energy π molecular orbital.
For ethyne, the bonding consists of one σ bond and two π bonds between the carbon atoms, with minimal interaction from the hydrogens.
Explanation:
- Ethene (C₂H₄): The key feature of ethene’s bonding is the presence of one σ bond and one π bond between the two carbon atoms. This allows for some flexibility in the bond, as the π bond is relatively weak compared to the σ bond.
- Ethyne (C₂H₂): In ethyne, the triple bond involves one σ bond and two π bonds, making it much stronger and shorter than ethene. The sp hybridization of the carbon atoms in ethyne results in a more linear molecule compared to the planar geometry of ethene.
These diagrams help visualize how the atomic orbitals combine to form molecular orbitals, influencing the properties and stability of the molecules.
