Name: London dispersion forces | Intermolecular forces and properties | AP Chemistry | Khan Academy
Uploaded: 2020-04-23T03:34:37.000Z
Duration: 9 min 38 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

- [Instructor] What we're going to do in this video

Relative clauses (Restrictive vs. nonrestrictive)

is start talking about forces that exist between

even neutral atoms, or neutral molecules.

we will talk about are London dispersion forces.

So it sounds very fancy but it's actually

a pretty interesting and almost intuitive phenomenon.

and let's just say we have a neutral atom.

So it has the same number of proton and electrons.

And then it'll have a cloud of electrons.

So I'm just imagining all these electrons

And let's imagine, and this is definitely not drawn to scale

the nucleus would actually be much smaller if it was.

But let's say that there's an adjacent atom

It could be different, but we're gonna say it's neutral.

And so if these are both neutral in charge,

how would they be attracted to each other?

And that's what London dispersion forces actually explain.

Because we have observed that even neutral atoms

and neutral molecules can get attracted to each other.

electrons are constantly jumping around, probabilistically.

They're in this probability density cloud

where an electron could be anywhere at any given moment.

But they're not always going to be evenly distributed.

where that left atom might look like this, just for moment,

where maybe slightly more of the electrons

are spending time on the left side of the atom

this is the Greek letter delta, lowercase delta,

And on this side, you might have a partial positive charge.

Because remember when it was evenly distributed

On the left side where most of the electrons are

Now what might this induce in the neighboring atom?

what might happen in the neighboring atom then.

Well we know that like charges repel each other

out here on the right side of this left atom,

well then the negative electrons might be

So they might be pulled a little bit to the left.

And so that will induce what is called a dipole.

So now you'll have a partial negative charge

and then a partial positive charge on the right side of it.

And we already had a randomly occurring dipole

on the left hand side, but then that would have

the separation of charge, where you have your

positive and negative charges at two different parts

of a molecule or an atom, or really anything.

But in this world, then all of a sudden these two characters

Or the atoms are going to be attracted to each other.

You can actually call London dispersion forces

as induced dipole, induced dipole forces.

because of what could start out as a temporary

imbalance of electrons, but then it induces

a dipole in the other atom, or the other molecule,

And that's all about a notion of polarizability.

How easy is it to polarize an atom or molecule?

And generally speaking, the more electrons you have,

which is usually associated with molar mass.

then the higher polarizability you're gonna have.

You're just gonna have more electrons to play around with.

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London dispersion forces | Intermolecular forces and properties | AP Chemistry | Khan Academy

constantly

significant

phenomenon

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