🧲 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.
📚 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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