London Dispersion Forces: Definition and Examples in Chemistry

📚 Quick Study Guide

⚛️ London Dispersion Forces (LDFs) are temporary attractive forces that occur when electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles. 💡 These forces are present in all molecules, whether they are polar or nonpolar. 🧪 The strength of LDFs increases with the size and shape of the molecule (more electrons = stronger LDFs). 🌡️ LDFs are also influenced by temperature; higher temperatures weaken these forces due to increased molecular motion. 📝 LDFs are the weakest of the intermolecular forces. 🔍 Examples include interactions between noble gases (He, Ne, Ar) and nonpolar molecules like methane ($CH_4$) or octane ($C_8H_{18}$).

🧪 Practice Quiz

1. Which of the following statements best describes London Dispersion Forces?
1. Temporary attractive forces between polar molecules.
2. Permanent attractive forces between nonpolar molecules.
3. Temporary attractive forces between all atoms and molecules.
4. Permanent attractive forces between all atoms and molecules.
2. What factor most significantly affects the strength of London Dispersion Forces?
1. The number of protons in the molecule.
2. The molecular weight and shape of the molecule.
3. The presence of hydrogen bonds.
4. The polarity of the molecule.
3. Which of the following molecules would exhibit the strongest London Dispersion Forces?
1. $CH_4$ (Methane)
2. $C_2H_6$ (Ethane)
3. $C_3H_8$ (Propane)
4. $C_4H_{10}$ (Butane)
4. London Dispersion Forces are primarily caused by:
1. The attraction between oppositely charged ions.
2. The presence of permanent dipoles.
3. The instantaneous fluctuations in electron distribution.
4. The sharing of electrons between atoms.
5. Which of the following substances relies *solely* on London Dispersion Forces for intermolecular attraction?
1. Water ($H_2O$)
2. Ammonia ($NH_3$)
3. Methane ($CH_4$)
4. Ethanol ($C_2H_5OH$)
6. How does increasing temperature typically affect London Dispersion Forces?
1. Increases their strength.
2. Decreases their strength.
3. Has no effect on their strength.
4. Causes them to become permanent.
7. Which of the following noble gases would you expect to have the highest boiling point due to London Dispersion Forces?
1. Helium (He)
2. Neon (Ne)
3. Argon (Ar)
4. Krypton (Kr)