Which is the strongest intermolecular force present between two molecules of BH_3?

• A. London dispersion forces
• B. Dipole-dipole interactions
• C. Hydrogen bonding
• D. Ion-dipole interactions

Answer: (A)

Verified step by step guidance

1. Step 1: Identify the molecular structure and polarity of BH_3. BH_3 (borane) has a trigonal planar shape with boron in the center bonded to three hydrogen atoms. Since the molecule is symmetrical, the bond dipoles cancel out, making BH_3 a nonpolar molecule.
2. Step 2: Understand the types of intermolecular forces. The main types are London dispersion forces, dipole-dipole interactions, hydrogen bonding, and ion-dipole interactions. Dipole-dipole and hydrogen bonding require polar molecules or specific atoms (like N, O, or F) bonded to hydrogen, and ion-dipole requires ions.
3. Step 3: Since BH_3 is nonpolar and contains no highly electronegative atoms bonded to hydrogen, it cannot exhibit dipole-dipole interactions or hydrogen bonding. Also, there are no ions present, so ion-dipole interactions are not possible.
4. Step 4: The only intermolecular force possible between BH_3 molecules is London dispersion forces, which arise from temporary fluctuations in electron density creating instantaneous dipoles even in nonpolar molecules.
5. Step 5: Conclude that the strongest intermolecular force present between two BH_3 molecules is London dispersion forces.