Question

Which of the following forces of attraction acts among the atoms in a molecule of type $\mathrm{B}-\mathrm{A}-\mathrm{B}$, where $\mathrm{A}$ and $B$ belong to group 16 and group 17, respectively?

• A. Dipole-dipole interaction
• B. Hydrogen bonding
• C. Van der Waals force
• D. Interionic attractions

Answer 1

The correct option is C

Van der Waals force

Explanation for the correct option:

• Group 16 elements are the Oxygen family in which Oxygen ($\mathrm{O}$), Sulphur ($\mathrm{S}$), Selenium($\mathrm{Se}$), Tellurium ($\mathrm{Te}$) and Polonium ($\mathrm{Po}$) are present. They are non-metals and are also known as Chalcogens.
• Group 17 elements are the Halogens in which Fluorine ($\mathrm{F}$), Chlorine ($\mathrm{Cl}$), Bromine ($\mathrm{Br}$), Iodine ($\mathrm{I}$) and Astatine ($\mathrm{At}$). They are also non-metals and are highly electronegative elements.

(C) Van der Waals force: The type of the molecule is $\mathrm{B}-\mathrm{A}-\mathrm{B}$, where $\mathrm{A}$ and $\mathrm{B}$ belongs to group 16 and group 17. Since both, groups are non-metals, the force of attraction between $\mathrm{A}$ and $\mathrm{B}$ will be Van der Waals forces because between two non-metals Van der Waals forces are present.

Explanation for the incorrect options:

(A) Dipole-dipole interaction: These forces of attraction occurs among the polar molecules. So, dipole-dipole interactions are formed between the atoms having a large difference in the electronegativities. Since the electronegativity of group 16 and group 17 have only small difference therefore, $\mathrm{B}-\mathrm{A}-\mathrm{B}$ cannot have dipole-dipole interaction.

(B) Hydrogen bonding: Hydrogen bonding is formed between the Hydrogen ($\mathrm{H}$) atom and highly electronegative elements like Fluorine ($\mathrm{F}$), Oxygen ($\mathrm{O}$), and Nitrogen ($\mathrm{N}$). Therefore, $\mathrm{B}-\mathrm{A}-\mathrm{B}$ cannot have Hydrogen bonding.

(D) Interionic attractions: Interionic attractions are formed between ions i.e., between cation and anion. The cation is a metal ion and the anion is a non-metal ion. For example, Sodium chloride ($\mathrm{NaCl}$) contains interionic interactions as the cation is Sodium ion (${\mathrm{Na}}^{+}$) and the anion is Chloride ion (${\mathrm{Cl}}^{-}$).

Therefore, the correct option is (C).