Chemistry S & P Block Elements UHS 2022
PMDC Verified Question 46 of 104
Why dimer of \( \text{AlCl}_3 \) is formed
A
Al is electron rich
B
Al is having lone pair of electron
C
Al donates lone pair to form bridge
D
Al forms co-ordinate bonds with chlorine to complete its octet
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: Al forms co-ordinate bonds with chlorine to complete its octet
Concept:

Molecules with incomplete valence shells (electron-deficient) will undergo structural rearrangement to achieve a stable octet, often forming coordinate covalent (dative) bonds.

Solution:

  • In a single molecule of Aluminum chloride (\( \text{AlCl}_3 \)), the central Aluminum atom forms 3 covalent bonds with 3 Chlorine atoms.
  • This means Aluminum only has 6 electrons in its valence shell (it is electron-deficient and lacks a full octet).
  • To achieve stability, two \( \text{AlCl}_3 \) molecules join together to form a dimer (\( \text{Al}_2\text{Cl}_6 \)).
  • A Chlorine atom from one molecule uses its lone pair to form a coordinate covalent bond with the electron-deficient Aluminum of the other molecule, and vice versa.
  • This mutually completes the octet for both Aluminum atoms.


Why other options are incorrect:

  • Option A & B: Aluminum is electron-deficient in \( \text{AlCl}_3 \), not electron-rich, and it has absolutely no lone pairs to donate.
  • Option C: It is the Chlorine atom that donates the lone pair, not the Aluminum.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

Previous Question All S & P Block Elements MCQs Next Question

Want to solve full-length papers under timed exam conditions?

Practice with zero-scroll lockdown sprints, dynamic latency zone timers, live peer selection telemetry, and the automated Amber mistake recovery loop.

Enter Arena Sprint iOS App Android App