Question

A group 13 element ‘X’ reacts with chlorine gas to produce a compound XCl₃. XCl₃ is electron deficient and easily reacts with NH₃ to form \[\ce{Cl3X –> NH3}\] adduct; however, XCl₃ does not dimerize X is ______.

Options

• B

• Al

• In

• Ga

Answer 1

A group 13 element ‘X’ reacts with chlorine gas to produce a compound XCl₃. XCl₃ is electron deficient and easily reacts with NH₃ to form \[\ce{Cl3X –> NH3}\] adduct; however, XCl₃ does not dimerize X is B.

Explanation:

\[\ce{B + Cl2 -> \underset{[\underset{(pπ-pπ) back bonding]}{does not dimerise due to}}{BCl3} ->[NH3] \underset{(adduct)}{Cl3B <- NH3}}\]

Although BCl₃ lacks an electron, it does not dimerize like Al, Ga, or In because a co-ordinate bond forms between a chlorine lone pair of electrons and an empty, unhybridized boron p-orbital, allowing pπ-pπ bonding to compensate for the chlorine's electron shortage.