What is the dispersion force? What does the magnitude of the dispersion force depend on? How can

step 1 Okay, so we're working on problem number 10 in chapter 11. So we'll talk about the dispersion fo

What is the dispersion force? What does the magnitude of the...

Key Concepts

Dispersion Force

A dispersion force is a type of intermolecular attraction that arises from instantaneous and temporary fluctuations in electron density, creating momentary dipoles in atoms and molecules. These transient dipoles induce similar dipoles in neighboring particles, leading to an attractive force. This concept is a fundamental aspect of van der Waals forces in physical chemistry and physics.

Polarizability

Polarizability refers to the ease with which the electron cloud around an atom or molecule can be distorted. A higher polarizability means that the electron cloud can more easily form temporary dipoles, thereby enhancing the strength of the dispersion forces. Polarizability is influenced by factors such as the size of the electron cloud and the number of electrons present.

Predicting Trends in Dispersion Forces

The magnitude of dispersion forces in closely related elements or compounds can often be predicted based on their molecular size, electron count, and overall polarizability. Generally, larger molecules or atoms with more electrons have more polarizable electron clouds and thus stronger dispersion forces. Additionally, structural aspects, like molecular shape and the ability to come into close contact, also play roles in determining the force's magnitude.

Transcript

00:06 Okay, so we're working on problem number 10 in chapter 11.

00:18 So we'll talk about the dispersion force here.

00:31 So what is the dispersion force and what types of interactions does it originate from? so in order to understand dispersion, you have to look at where the actual intermolecular forces come from in neutral molecules when they're interacting.

00:48 So let's take two atoms.

00:50 So atoms generally, if we're not told otherwise, we're going to assume that atoms have a spherically symmetric shell of electrons around them.

01:01 So we use one example here.

01:06 So we can interact with another one, spherically symmetric.

01:11 And when you bring these two charged clouds together, they're actually neutral overall because in the core here, you have plus one charge clouds.

01:22 Charge, but around the outside, you end up with a minus one charge, right? and it isn't, the minus one charge isn't all in one place, right? it's spread out around the entire sphere.

01:41 So what that means is, because it's kind of fluid, it does act like a kind of fluid, almost like a liquid, except much, much faster.

01:53 So when you bring two atoms, molecules close together in this case we'll use atoms you end up with a one negatively charged region because remember we're bringing these together not with their centers at their their nuclei at the same point so that they feel everything all at once we're bringing these two kind of regions close to one another they feel each other first and so this region both regions are going to end up changing shape because remember what charges do the kulom force.

02:30 So here's a negative one charge and another negative one point charge.

02:35 And when i bring those two close together, they feel a force between one another, which is proportional to 1 over r square, their distance.

02:48 So this being r, the distance between the two.

02:52 So the force is proportional to that.

02:55 And that's what is happening except for every point in these regions.

03:01 Okay? so i guess the question is, how would i be able to distinguish for two different very similar atoms or molecules, whether one would experience more dispersion force or less? so let's try that.

03:21 So imagine, let's try a.

03:24 I'm not going to give these names.

03:26 A, pretend they're very similar and similar for nuclei.

03:33 Okay, you can pretend that they're both the same.

03:35 And they're both neutral.

03:37 Maybe they're close together on the periodic table.

03:41 But how would i tell the difference between a and b? if they're very similar, they're very close to one another on the periodic table...