Answer: F's lone pair back-donation into B's empty p orbital reduces electron deficiency more than Cl.
- A F's lone pair back-donation into B's empty p orbital reduces electron deficiency more than Cl
- B Fluorine is generally more electronegative, which alone explains the lower acidity in typical laboratory settings
- C BCl3 is a physically larger molecule than BF3 in every dimension under usual circumstances
- D BF3 has shorter B-F bonds, which alone reduces its Lewis acidity according to most researchers
Correct answer: A. F's lone pair back-donation into B's empty p orbital reduces electron deficiency more than Cl
Explanation: F is a better pi-donor than Cl (smaller, better size match with B 2p); back-bonding in BF3 partially fills B's vacant orbital more effectively, reducing Lewis acidity.
Diamond's rigid 3D tetrahedral network makes it the hardest natural material, while graphite's flat hexagonal sheets are held together only by weak forces, letting them slide past each other (used as a lubricant and in pencils).
Concept context
Covers the Boron family (Group 13: B, Al) and the Carbon family (Group 14: C, Si, Ge, Sn, Pb). Key topics include Lewis acid behaviour of BF₃, borax bead test, silicates, silicones, allotropes of carbon, and trends in properties down the group.