🧲 DAT Intermolecular Forces Explained: Hydrogen Bonding, Dipole, and Dispersion

Intermolecular forces (IMFs) describe how molecules interact with each other—playing a key role in boiling point, melting point, solubility, and molecular behavior. The DAT regularly includes questions about recognizing IMF types and how they affect physical properties.

🧪 Master Periodic Trends for the DAT: Ionization Energy, Atomic Radius, Electronegativity

📚 The Three Main Types of IMFs

1. London Dispersion Forces (Van der Waals)

  • Present in all molecules, but especially important in nonpolar molecules

  • Caused by temporary dipoles due to electron movement

  • Weakest type of IMF

📌 Example: Cl₂, CH₄, noble gases

2. Dipole–Dipole Interactions

  • Occur between polar molecules

  • Positive end of one molecule aligns with negative end of another

📌 Example: HCl, SO₂

3. Hydrogen Bonding

  • A special case of dipole-dipole

  • Occurs when hydrogen is bonded to N, O, or F

  • Strongest of the IMFs

📌 Example: Water (H₂O), Ammonia (NH₃)

🧠 How IMFs Affect Physical Properties

Property Stronger IMF Means…
Boiling Point Higher
Melting Point Higher
Vapor Pressure Lower
Viscosity Higher
Solubility “Like dissolves like” applies

DAT questions will often ask you to compare boiling points or predict solubility based on IMF strength.

🧪 DAT Question Examples

Which of the following has the highest boiling point?

  • CH₄

  • NH₃

  • CO₂

  • Ne

Answer: NH₃ → due to hydrogen bonding

Which IMF is present in all molecules regardless of polarity?

Answer: London Dispersion

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✅ Summary

  • London Dispersion: Weak, in all molecules

  • Dipole–Dipole: Moderate, in polar molecules

  • Hydrogen Bonding: Strongest, requires N, O, or F bonded to H

  • IMFs affect boiling point, melting point, solubility, and more

  • Memorize trends and look out for DAT trap answers like nonpolar molecules with high mass



 

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