Molecular orbital theory explains that orbital mixing occurs when atomic orbitals combine to form molecular orbitals, but this mixing is not uniform across all elements. In diatomic molecules like B2, the sigma 2p bonding orbital is promoted to a higher energy level due to mixing with s and p orbitals, while in O2 and F2, this mixing does not occur in the same way. The key factor influencing whether mixing happens is the energy levels of the orbitals involved and the specific electron configurations of the elements. Understanding the conditions under which mixing occurs can clarify the behavior of molecular orbitals in different diatomic molecules. Overall, the presence or absence of orbital mixing is determined by the relative energy levels and interactions of the atomic orbitals involved.
