Chemistry220 views·Updated 24 Jun 2026·3 pages

Understanding Intermolecular Bonds: London Dispersion, Dipoles, and Hydrogen Bonds

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Intermolecular bonds are found between molecules.
They are also known as Von der Waals forces, and there are several
types to consider:
Lond

Intermolecular Bonds and London Dispersion Forces

Intermolecular bonds occur between separate molecules and are weaker than the bonds within molecules. These Van der Waals forces come in three main types, with increasing strength: London Dispersion forces, Permanent dipole-Permanent dipole interactions, and Hydrogen bonding.

London Dispersion forces are the weakest type but exist between all atoms and molecules. They explain why even noble gases and molecular elements can condense into liquids and solids at low temperatures. These forces arise from temporary uneven distributions of electrons, creating momentary δ+ and δ- regions that attract neighboring molecules.

The strength of London Dispersion forces increases with molecular size. Larger atoms and molecules have more electrons, which can create stronger temporary dipoles and therefore stronger attractions between molecules.

Remember this: London Dispersion forces are universal – they occur between all molecules regardless of structure, unlike other intermolecular forces which require specific molecular features.

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Permanent Dipole-Permanent Dipole Interactions

Polar molecules have permanent dipoles – regions of partial positive and negative charge that don't shift over time. When these molecules encounter each other, the positive end of one molecule attracts the negative end of another, creating permanent dipole-permanent dipole interactions.

These interactions are stronger than London Dispersion forces when comparing molecules with similar numbers of electrons. You'll find them in molecules with certain shapes: linear, angular, and trigonal pyramidal compounds containing polar bonds will be polar overall.

Molecular shape determines whether a molecule is polar. For example, tetrahedral molecules with four identical groups around the central atom (like CCl₄) are non-polar despite having polar bonds, because the bond dipoles cancel out. However, if one group differs (like in CHCl₃), the molecule becomes polar.

Quick tip: To determine if permanent dipole interactions will occur, first check if the molecule has polar bonds, then analyze its shape to see if those bond dipoles create an overall molecular dipole.

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Hydrogen Bonding and Bonding Strength

Hydrogen bonding is the strongest type of intermolecular bond. These special permanent dipole interactions occur when hydrogen is bonded to highly electronegative atoms: nitrogen, oxygen, or fluorine $remember as H-NOF$ . Common examples include water, ammonia, alcohols, and alkanoic acids.

The exceptional strength of hydrogen bonds significantly impacts physical properties. Substances with hydrogen bonding have much higher melting and boiling points than you'd expect based on their molecular size and electron count alone. This explains why water, despite its small molecular size, has surprisingly high boiling and melting points.

Van der Waals forces increase in strength from London Dispersion forces (weakest) to permanent dipole-permanent dipole interactions to hydrogen bonding (strongest). However, even the strongest intermolecular forces are weaker than actual covalent bonds that hold atoms together within molecules.

Exam focus: Questions often ask you to explain physical property differences between similar compounds. If one can form hydrogen bonds while the other cannot, this is usually the key to explaining boiling point differences.

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Chemistry220 views·Updated 24 Jun 2026·3 pages

Understanding Intermolecular Bonds: London Dispersion, Dipoles, and Hydrogen Bonds

Sophieeee 🎀👝🛍🌺💓@sophiesnotes

Add to Google sources

Intermolecular bonds are the forces that hold molecules together, distinct from the bonds within molecules themselves. These forces, collectively known as Van der Waals forces, vary in strength and play crucial roles in determining the physical properties of substances like...

of 3

Intermolecular Bonds and London Dispersion Forces

Remember this: London Dispersion forces are universal – they occur between all molecules regardless of structure, unlike other intermolecular forces which require specific molecular features.

of 3

Permanent Dipole-Permanent Dipole Interactions

Quick tip: To determine if permanent dipole interactions will occur, first check if the molecule has polar bonds, then analyze its shape to see if those bond dipoles create an overall molecular dipole.

of 3

Hydrogen Bonding and Bonding Strength

Exam focus: Questions often ask you to explain physical property differences between similar compounds. If one can form hydrogen bonds while the other cannot, this is usually the key to explaining boiling point differences.