Which one of the following conditions is not correct for the combination of atomic orbitals to form molecular orbitals ?
[amp_mcq option1=”The combining atomic orbitals must have same or nearly the same energy.” option2=”The combining atomic orbitals must show lateral overlap with each other.” option3=”The combining atomic orbitals must have the same symmetry about the molecular axis.” option4=”The combining atomic orbitals must overlap to the maximum extent.” correct=”option2″]
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UPSC Geoscientist – 2024
1. **The combining atomic orbitals must have comparable energies.** This allows for effective interaction and mixing of orbitals. (Statement A is correct)
2. **The combining atomic orbitals must have the same symmetry about the molecular axis.** Orbitals with different symmetries (e.g., s orbital and p$_x$ orbital if the molecular axis is z) cannot effectively overlap. (Statement C is correct)
3. **The combining atomic orbitals must overlap to the maximum possible extent.** Significant overlap leads to strong bonding (and antibonding) molecular orbitals. (Statement D is correct)
Statement B claims that combining atomic orbitals *must* show lateral overlap. This is incorrect. Atomic orbitals can overlap axially (end-to-end), which leads to the formation of sigma ($\sigma$) molecular orbitals, or laterally (side-by-side), which leads to the formation of pi ($\pi$) molecular orbitals. Both types of overlap are valid and common ways for atomic orbitals to combine. It is not a requirement that *only* lateral overlap must occur. For instance, the formation of H₂ molecule involves axial overlap of two 1s orbitals.