intermolecular forces
Overview
This lesson explores intermolecular forces (IMFs), the attractive forces between molecules. Understanding IMFs is crucial for explaining the physical properties of substances, such as boiling points, melting points, and solubility, which are significantly weaker than intramolecular (covalent or ionic) bonds.
Introduction to Intermolecular vs. Intramolecular Forces
It is essential to distinguish between **intermolecular forces (IMFs)** and **intramolecular forces**. Intramolecular forces are the strong chemical bonds *within* a molecule (e.g., covalent bonds, ionic bonds), which determine the molecule's chemical properties and stability. IMFs, on the other han...
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Key Concepts
- Intermolecular Forces (IMFs): Attractive forces that exist between molecules.
- Intramolecular Forces: Forces that exist within a molecule, such as covalent or ionic bonds.
- Van der Waals Forces: A collective term for London Dispersion Forces and Dipole-Dipole interactions.
- London Dispersion Forces (LDFs): Weak, temporary attractive forces arising from instantaneous dipoles due to random electron movement.
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Exam Tips
- →Always state the *type* of intermolecular force (LDF, dipole-dipole, hydrogen bond) and *explain how it arises* (e.g., 'due to instantaneous dipoles' or 'due to permanent dipoles').
- →When comparing boiling points, systematically identify all IMFs present in each substance. Remember LDFs are always present. Then, compare the strengths: Hydrogen bonding > Dipole-dipole > LDFs (for similar molar masses). If only LDFs, compare based on molar mass/surface area.
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