Question

BCl₃ does not exist as a dimer but BH₃ exists as a dimer (B₂H₆) because

• A. chlorine is more electronegative than hydrogen
• B. there is pπ - pπ back bonding in BCl3 and BH3 does not contain such multiple bonding
• C. large sized chlorine atoms do not fit in between the small boron atoms where as small sized hydrogen atoms get fitted in between boron atoms
• D. none of the above

Answer 1

The correct option is C

large sized chlorine atoms do not fit in between the small boron atoms where as small sized hydrogen atoms get fitted in between boron atoms

Explanation for the correct answer:

Dimer — A dimer is a type of oligomer that is formed by chemically bonding two monomers that are simpler compound

Diborane$\{$ ${\mathrm{B}}_2{\mathrm{H}}_6$ $\}$ ---- It is a chemical compound consisting of boron and hydrogen.

• It is a colourless, pyrophoric gas with a repusively sweet odor
• it has attracted wide attention for its electronic dot structure
• large-sized chlorine atoms do not fit in between the small boron atoms whereas small-sized hydrogen atoms get fitted in between boron atoms.

Explanation for the incorrect answer:

Option a ] chlorine is more electronegative than hydrogen, electronegativity does not play a role to arrange the molecules in dimer form

option b ] there is pπ - pπ back bonding in BCl3 and BH3 does not contain such multiple bonding, in diborane back bonding doesn't occur

option c ] large-sized chlorine atoms do not fit in between the small boron atoms whereas small-sized hydrogen atoms get fitted in between boron atoms

Thus, the option {c} is correct.