what's the difference between vanderwaals forces and dipole dipole interaction
Van Der Walls forces account for both weak dipole dipole interactions in slightly polar molecules and for even weaker interactions between nonpolar molecules. London Forces are specifically limited to weaker interactions between nonpolar molecules. One is more general than the other (at least that is my understanding anyways), but the two terms can be used (scratch that..."are" used) interchangeably to mean weak interactions between non-polar molecules.
antoine.frostburg.edu/chem/senese/101/liquids/faq/h-bonding-vs-london-forces.shtml
Van der Waals forces and dipole-dipole interactions are both types of intermolecular forces, which are the forces of attraction between molecules. However, there are some distinct differences between these two types of forces.
Van der Waals forces are relatively weak attractive forces that exist between all molecules, regardless of whether they are polar or non-polar. These forces are caused by temporary fluctuations in electron distribution within molecules, resulting in the creation of temporary dipoles. Van der Waals forces can be further categorized into three types:
1. London dispersion forces: These are the weakest type of Van der Waals forces and occur between non-polar molecules. It happens when temporary dipoles induce other temporary dipoles in neighboring molecules. These induced dipoles create a weak attractive force between the molecules.
2. Dipole-induced dipole interactions: This occurs when a polar molecule induces a temporary dipole in a neighboring non-polar molecule. The partial charges in the polar molecule attract the opposite charges in the non-polar molecule, resulting in an attractive force between them.
3. Induced dipole-induced dipole interactions: This occurs between non-polar molecules. Similar to London dispersion forces, temporary fluctuations in electron distribution in one molecule induce temporary fluctuations in a neighboring molecule, resulting in an attractive force between them.
On the other hand, dipole-dipole interactions occur between polar molecules. A polar molecule has a permanent dipole moment, meaning it has a separation of positive and negative charges. The positive end of one polar molecule is attracted to the negative end of another polar molecule, resulting in an attractive force between them.
To summarize:
- Van der Waals forces are relatively weaker forces that can occur between all molecules.
- Dipole-dipole interactions are stronger forces that occur specifically between polar molecules.
To determine the presence and magnitude of these forces in a given situation, it is important to consider the polarity of the molecules involved and the nature of their electron distribution.