Question

Bond polarity of diatomic molecules is because of
(A) difference in electron affinities of two atoms
(B) difference in electronegativity of two atoms
(C) difference in ionisation potentials
(D) all of above

Answer 1

Hint: A diatomic molecule (containing two atoms) in which two atoms are bonded with a chemical bond, can be a covalent or ionic bond. Covalent bonds are of further two types, polar or nonpolar covalent bonds. A covalent bond will be polar when there is charge separation, partially but not complete. If charge separation occurs completely, then the chemical bond will be considered to be ionic.

Complete Step by Step Solution:
For a covalent bond to be polar, it is important to occur partial charge separation. Partial charge separation means at one pole of the molecule positive charges accumulate (more nucleus) and on the other pole negative charges accumulate (more electrons).

When an atom (large size) has less tendency to attract the electron of bond, attains partial positive charge, and when an atom (small size and high nuclear charge) has a great tendency to attract the outermost electron it attains partial negative charge.

The tendency with which an atom attracts electrons of another atom (bonded with a covalent bond) is known as electronegativity. For partial charge separation electronegativity of one atom of a molecule should be less so that it has less affinity towards electrons and attain a partial positive charge on one pole of the molecule. Whereas electronegativity of another atom of a molecule should be more so that it can easily attract an electron pair of covalent bonds (just attract and not gained) and attain partial negative charge. So, the more the electronegativity difference the more will be polarity (partial transfer of electrons) in the molecule.
Thus, the correct option is B.

Note: Due to the difference in ionisation potential (ionisation energy), the chemical bond terms as ionic, and in this case, one atom of the molecule will lose electrons easily (low IE) and another atom of the molecule will accept electrons completely (high IE).Thus, the charge will separate completely and thus bond will be ionic. The difference in electron affinity also does not contribute toward polarity of the molecule as one atom of the molecule will have a great affinity to accept electrons and another atom of the molecule has less affinity to accept electrons thus forming a somewhere ionic character.