How many bonding and antibonding molecular orbitals are there in methane, CH4?
Bonding orbitals Antibonding orbitals
Zero Zero
One One
Two Two
Three Three
Four Four
The Correct Answer and Explanation is:
In methane (CH₄), there are four bonding molecular orbitals and zero antibonding molecular orbitals. Thus, the correct answer is Four bonding orbitals, Zero antibonding orbitals.
Explanation
Methane (CH₄) is a simple molecular compound where one carbon atom is bonded to four hydrogen atoms. The bonding in methane can be understood using the concept of molecular orbitals, which form when atomic orbitals combine.
- Hybridization: In methane, the carbon atom undergoes sp³ hybridization, meaning that one 2s and three 2p atomic orbitals mix to form four equivalent sp³ hybrid orbitals. These four sp³ orbitals are oriented tetrahedrally, allowing for optimal overlap with the 1s orbitals of the four hydrogen atoms.
- Bonding Orbitals: Each of the four sp³ hybrid orbitals of carbon overlaps with a 1s orbital of a hydrogen atom, creating four sigma (σ) bonds. These bonds are the bonding molecular orbitals of methane. The electron density in these bonding orbitals is concentrated between the nuclei of the carbon and hydrogen atoms, which stabilizes the molecule.
- Antibonding Orbitals: Antibonding molecular orbitals, typically denoted with an asterisk (σ*), are formed from the out-of-phase combination of atomic orbitals. In the case of methane, since all bonding orbitals are formed from the constructive overlap of orbitals, there are no out-of-phase combinations that lead to antibonding orbitals. Thus, CH₄ does not possess any antibonding molecular orbitals.
- Conclusion: Therefore, in methane, there are four bonding molecular orbitals arising from the overlap of the sp³ hybrid orbitals of carbon with the 1s orbitals of hydrogen, and there are zero antibonding molecular orbitals. This arrangement accounts for the stability and tetrahedral geometry of the methane molecule, which is crucial for its chemical properties and reactivity.