Question

The H-F and the H-I bond have different values for their bond polarity. Which of the following statements correctly identifies the bond that is more polar and gives the correct reason for this difference?
(A) The H-F bond is more polar than the H-I bond because iodine is more electronegative than fluorine.
(B) The H-F bond is more polar than the H-I bond because fluorine is more electronegative than iodine.
(C) The H-I bond is more polar than the H-F bond because iodine is more electronegative than fluorine.
(D) The H-I bond is more polar than the H-F bond because fluorine is more electronegative than iodine.

Answer 1

Hint: (1) Polar bond refers to the type of covalent bond in which there is unequal sharing of electrons between the two atoms.
(2) Non-polar bond refers to the type of covalent bond in which there is equal sharing of electrons between the two atoms.

Complete step-by-step answer: Due to unequal sharing of electrons between the two atoms in a polar covalent bond, one end of the molecule acquires a partial positive charge and the other end of the molecule acquires a partial negative charge. Due to equal sharing of electrons between the two atoms in a nonpolar covalent bond, there are no partial charges on the molecule.
Thus, electrons are not always shared equally between the two bonding atoms. One of the atoms might exert more force on the electron cloud than the other, this is called electronegativity. An atom’s electronegativity indicates how strongly the atom can pull the electrons towards itself. The electronegativity values of the two bonding atoms highly affect the polarity of the bond between the atoms. The difference in electronegativities between bonded atoms can indicate whether a bond is polar, non-polar or ionic.
Now, the two molecules mentioned in the question are HF and HI. Let us first determine the polarity of these two molecules. The electronegativity of fluorine is more than hydrogen. So, the fluorine atom will exert a greater pull on the electrons than the hydrogen atom. Hence, the H-F bond is polar. Similarly, the electronegativity of iodine is more than hydrogen. So, the iodine atom will exert a greater pull on the electrons than the hydrogen atom. Hence, the H-I bond is also polar. Thus, both H-F and H-I bonds are polar covalent bonds. But, electronegativity values decrease down a group and fluorine and iodine belong to the same group (Group 17) of the periodic table. Thus, fluorine is more electronegative than iodine and so H-F bond will be more polar than H-I bond.
So, the correct option is (B).

Note: As the electronegativity differences between the bonding atoms in a diatomic molecule increases, the polarity of the bond between the atoms also increases.