We need to know some characteristics of electronegative elements and how do they influence bonding molecular orbitals. Electronegativity is the tendency of an element to attract a shared pair of electrons towards itself. The term electronegativity generally means deficient of electrons and hence attracts the same. Bonding between two electronegative elements is through covalent bonding (bond formation by sharing a pair of electrons) if the difference in their electronegativities is equal or less.Complete step by step answer:
We have to remember that the homonuclear diatomic molecules feature relatively ‘pure’ covalent bonds since the electronegativities of the bonded atoms are the same. Heteronuclear diatomic molecules have atoms with different electro negatives and hence tend to become polarized.
-The electrons attracted by an electronegative element in case of a Heteronuclear diatomic molecule are closer to the more electronegative atom because the orbitals associated with the atom are lower in energy than orbitals associated with the other atom.
-For the two most electronegative elements, O and F, the 2s orbitals are especially low in energy. Their 2p orbitals are stabilized as well but to a much lower extent. The result is an especially large energy gap between the 2s and 2p atomic orbitals of oxygen and fluorine.
-As given in the question, In a Heteronuclear diatomic molecule AB, where A is more electronegative than B. The molecular orbital diagram is as follows:
Since the electrons shift more towards A due to its more electronegative character hence bonding molecular orbital resembles the character of A more than that of B.Therefore the correct option is option (B).Note:
It must be noted that when an electronegative element attracts an electron, it becomes more stabilized in nature and hence has low energy. The atom from which the more electronegative elements attract the electrons becomes excited due to deficiency, it becomes more stabilized in nature and hence has low energy. The atom from which the more electronegative elements attracts the electrons becomes excited due to deficiency of electrons and hence have higher energy as depicted in a molecular orbital diagram above.