Dipole Dipole Forces vs. London Dispersion Forces — What's the Difference?
Edited by Tayyaba Rehman — By Fiza Rafique — Published on January 9, 2024
Dipole Dipole Forces arise between molecules with permanent dipoles, whereas London Dispersion Forces are temporary attractions between all molecules, including non-polar ones.
Difference Between Dipole Dipole Forces and London Dispersion Forces
Table of Contents
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Key Differences
Dipole Dipole Forces and London Dispersion Forces are two primary types of van der Waals forces that influence the interactions between molecules. Dipole Dipole Forces specifically occur between polar molecules, which possess a permanent dipole due to differences in electronegativity between bonded atoms. This results in a positive end and a negative end within a molecule. When such polar molecules come close to one another, the positive end of one molecule attracts the negative end of another, leading to Dipole Dipole Forces.
On the other hand, London Dispersion Forces, also known as instantaneous dipole-induced dipole attractions, manifest even in non-polar molecules. They arise from temporary fluctuations in electron distribution around a molecule, leading to momentary dipoles. These transient dipoles induce dipoles in neighboring molecules, leading to a temporary attraction known as London Dispersion Forces. Notably, while every molecule, polar or non-polar, experiences London Dispersion Forces, only polar molecules experience Dipole Dipole Forces.
The strength of Dipole Dipole Forces generally depends on the polarity of the molecules. The more polar the molecule, the stronger the Dipole Dipole Forces. Conversely, London Dispersion Forces grow stronger with increased molecular size or electron count. This is because larger molecules or those with more electrons have a greater capacity for electron shifting, leading to more pronounced temporary dipoles.
Both Dipole Dipole Forces and London Dispersion Forces play pivotal roles in determining the physical properties of substances, such as boiling and melting points. While the presence of Dipole Dipole Forces can elevate the boiling point of a polar substance compared to a non-polar one of similar size, London Dispersion Forces can cause significant elevation in boiling points for large non-polar molecules.
Comparison Chart
Origin of Force
Permanent dipoles in polar molecules.
Temporary fluctuations in electron distribution.
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Molecules Involved
Only polar molecules.
All molecules, including non-polar ones.
Dependence
Electronegativity difference between bonded atoms.
Molecular size or electron count.
Strength Relative to Molecular Size
Independent of molecular size, depends on molecular polarity.
Increases with molecular size or electron count.
Examples
HCl, HBr.
He, Ne, Ar.
Compare with Definitions
Dipole Dipole Forces
They arise due to permanent molecular dipoles.
The Dipole Dipole Forces in water result from the molecule's bent shape and polar O-H bonds.
London Dispersion Forces
They affect all molecules, irrespective of their polarity.
London Dispersion Forces exist in both polar HCl and non-polar O2 molecules.
Dipole Dipole Forces
Dipole Dipole Forces are attractions between polar molecules.
In a sample of HCl gas, Dipole Dipole Forces keep the molecules close together.
London Dispersion Forces
These forces grow stronger with increasing molecular size.
Xe experiences stronger London Dispersion Forces than He due to its larger size.
Dipole Dipole Forces
These forces depend on the molecule's polarity.
Highly polar HF molecules experience strong Dipole Dipole Forces.
London Dispersion Forces
London Dispersion Forces result from momentary electron fluctuations.
Even in non-polar He gas, London Dispersion Forces cause weak attractions between atoms.
Dipole Dipole Forces
Dipole Dipole Forces influence properties like boiling and melting points.
Due to Dipole Dipole Forces, polar HBr has a higher boiling point than non-polar I2 of similar size.
London Dispersion Forces
London Dispersion Forces are the only van der Waals forces in non-polar substances.
In a sample of methane, CH4, London Dispersion Forces dominate intermolecular interactions.
Dipole Dipole Forces
Only molecules with differing electronegativity experience these forces.
In polar NCl₃, the Dipole Dipole Forces arise from the difference in electronegativity between N and Cl.
London Dispersion Forces
They arise due to temporary dipoles inducing dipoles in neighboring molecules.
In Ar gas, London Dispersion Forces form as electron cloud shifts create temporary dipoles.
Common Curiosities
Can non-polar molecules experience London Dispersion Forces?
Yes, all molecules, including non-polar ones, experience London Dispersion Forces.
Are Dipole Dipole Forces always present in polar molecules?
Yes, any molecule with a permanent dipole will exhibit Dipole Dipole Forces when near other polar molecules.
Why do larger non-polar molecules have higher boiling points?
Larger non-polar molecules have more electrons, leading to stronger London Dispersion Forces and higher boiling points.
What molecules primarily exhibit Dipole Dipole Forces?
Dipole Dipole Forces primarily affect polar molecules with permanent dipoles.
Why might two polar molecules have different Dipole Dipole Force strengths?
Differences in molecular structure and the electronegativity of bonded atoms can influence Dipole Dipole Force strengths.
Which force is generally stronger in small molecules?
In small molecules, if one is polar, Dipole Dipole Forces would typically be stronger than London Dispersion Forces.
Can a molecule experience both types of forces simultaneously?
Absolutely. Polar molecules experience both Dipole Dipole Forces and London Dispersion Forces.
How do London Dispersion Forces originate in non-polar molecules?
They arise from temporary fluctuations in electron distribution, creating momentary dipoles.
Does the strength of Dipole Dipole Forces relate to molecular size?
Not directly. The strength of Dipole Dipole Forces relates more to the molecule's polarity than its size.
Are London Dispersion Forces significant in large polar molecules?
Yes, even in large polar molecules, London Dispersion Forces can play a significant role alongside other forces.
How does molecular geometry affect Dipole Dipole Forces?
Molecular geometry can influence whether a molecule has a net dipole, thus affecting Dipole Dipole Force strength.
Are London Dispersion Forces the weakest intermolecular forces?
In small molecules, they're typically weaker than Dipole Dipole Forces but can be significant in larger molecules.
How do London Dispersion Forces affect gases like helium or neon?
They cause weak attractions between atoms, influencing properties like condensation and boiling points.
What role do electron clouds play in London Dispersion Forces?
Fluctuations in electron clouds create temporary dipoles, which are central to London Dispersion Forces.
Can a substance be non-polar overall but still have regions of polarity?
Yes, molecules can have polar bonds but be non-polar overall due to symmetric geometry, leading to no net dipole.
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Written by
Fiza RafiqueFiza Rafique is a skilled content writer at AskDifference.com, where she meticulously refines and enhances written pieces. Drawing from her vast editorial expertise, Fiza ensures clarity, accuracy, and precision in every article. Passionate about language, she continually seeks to elevate the quality of content for readers worldwide.
Edited by
Tayyaba RehmanTayyaba Rehman is a distinguished writer, currently serving as a primary contributor to askdifference.com. As a researcher in semantics and etymology, Tayyaba's passion for the complexity of languages and their distinctions has found a perfect home on the platform. Tayyaba delves into the intricacies of language, distinguishing between commonly confused words and phrases, thereby providing clarity for readers worldwide.
