Factors affecting Instantaneous Dipole-Induced Dipole Attraction

In this video we want to discuss the factors affecting the intermolecular forces of attraction between non-polar molecules.

There are several different names of this type of attraction:

- instantaneous dipole-induced dipole attraction

- temporary dipole-induced dipole attraction

- dispersion forces

- Van Der Waals forces

For this discussion let's use instantaneous dipole-induced dipole attraction or id-id attraction for short.

There are 2 factors affecting id-id attraction: electron cloud size and surface area.

factors affecting id id attraction concept map

Electron cloud size is the dominant factor hence if there is a difference in electron cloud size or the number of electrons, we will be focusing on this to compare id-id attraction strength.

When electron cloud size is the same, then we will look at the surface area for molecular interaction to compare strength of id-id attraction.

1. Size of Electron Cloud

When a non-polar molecule has a bigger electron cloud, distortion of its electron cloud will form a stronger instantaneous dipole, or we can say that the bigger electron cloud is more polarisable.

factors affecting id id attraction compare electron cloud size and polarisability

In the above example, we can see that the bigger molecule with 6 electrons can form a stronger instantaneous dipole than the smaller molecule with 2 electrons.

Hence the id-id attraction for the bigger molecule will be stronger.

In general, the bigger the electron cloud of the molecule, the more polarisable it will be, and the stronger the id-id attraction between molecules.

2. Surface Area for Molecular Interaction

For a more spherical molecule, its surface area will be smaller hence there will be less interaction with its neighboring molecules and id-id attraction will be weaker.

factors affecting id id attraction compare surface area for molecular interaction with different shapes

In this example we can see that the molecule which is long and flat will have a much bigger surface area to interact with its neighbours (highlighted in orange).

The spherical molecule on the other hand has significantly less interaction (highlighted in orange) with its neighbours.

Therefore the more spherical the molecule, the smaller the surface area for molecular interaction, and the weaker the id-id attraction between molecules.

For the in-depth discussion on factors affecting the intermolecular forces of attraction between non-polar molecules, check out this video!

Topic: Intermolecular Forces, Physical Chemistry, A Level Chemistry, Singapore

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