(a) Which kind of intermolecular attractive force is shown in each case here? (b) Predict which

step 1 Today we will be having a look at intermolecular forces. Let's start by talking about the six di

(a) Which kind of intermolecular attractive force is shown...

Key Concepts

Relative Strength of Intermolecular Interactions

Understanding the relative strength of intermolecular interactions is essential in predicting physical properties. Generally, hydrogen bonds are the strongest among the common intermolecular forces, followed by dipole-dipole interactions, with London dispersion forces being the weakest. This hierarchy helps in predicting which interaction will have the least influence on molecular behavior under various conditions.

London Dispersion Forces

London dispersion forces, also known as instantaneous dipole-induced dipole attractions, are present in all molecules, whether polar or nonpolar. These weak intermolecular forces arise due to the temporary fluctuations in electron distribution within molecules, making them particularly significant in larger or more polarizable molecules.

Hydrogen Bonding

Hydrogen bonding is a particularly strong type of dipole-dipole interaction that occurs when hydrogen is covalently bonded to a highly electronegative atom (such as nitrogen, oxygen, or fluorine) and experiences an attraction to a lone pair of electrons on a nearby electronegative atom. This interaction is crucial in many chemical and biological structures.

Intermolecular Forces

Intermolecular forces are the attractions that occur between molecules. They play a key role in determining the physical properties of substances, such as boiling points, melting points, and solubilities. These forces include hydrogen bonding, dipole-dipole interactions, and London dispersion forces, among others, and vary in strength depending on the molecular characteristics.

Dipole-Dipole Interactions

Dipole-dipole interactions occur between molecules that possess permanent dipole moments. These attractive forces result from the electrostatic attractions between the partially positive end of one molecule and the partially negative end of another molecule, influencing the behavior of polar substances.

Transcript

00:01 Today we will be having a look at intermolecular forces.

00:03 Let's start by talking about the six different types of intermolecular forces before we get into the problem.

00:10 So there is dipole dipole, hydrogen bonding, ion dipole, ion induced dipole, and finally, or as some people like to call it, london forces.

01:25 So let's start off with ion induced dipole force.

01:29 And i feel like the name gives away what it is actually about.

01:32 It is an ion which induces a dipole.

01:36 So a positive or negative ion needs to be present, which means a cation or an anion should be present, as shown in the image.

01:52 And this charge here can be induced onto neighboring molecules.

02:02 So this force needs two components.

02:05 It needs an ion, something that is charged, and something that is neutral.

02:16 The ion approaches the non -polar atom or molecule, which is neutral, and it causes distortion in the electron cloud of the non -polar molecule, which results in an electrostatic attraction, as we can see here.

02:30 This molecule here has no dipole, has no charge, completely neutral, and then an ion comes into the picture.

02:39 And then it disrupts the electron cloud that we see here.

02:45 This is the electron cloud here.

02:47 It disrupts the electron cloud and induces a dipole.

02:52 Now moving on to dispersion forces, aka london forces, what you need to know about it is that every molecule, every ion has them.

03:02 Every molecule will have these forces.

03:05 And they come up due to the electron cloud being disrupted.

03:09 So, every molecule has one.

03:26 They may be the dominant intermoleful force in some molecules, and they might not be in some, there might be hydrogen pointing as a dominant molecule for some molecules, but you need to remember that every molecule has lundered forces.

03:40 It is caused from the result of changes in electron density distribution in an atom or molecule.

03:47 A temporary dipole forms in an atom or non -polar molecule that is then attracted to another non -polar or atom.

04:02 So let's have a look in the image.

04:04 Here we can see that there is a symmetrical distribution of electrons.

04:09 But obviously electrons are not in one place.

04:12 They are continuously moving.

04:14 And because of this continuous movement, it will cause an instantaneous dipole, which is also the same thing as a temporary dipole.

04:20 And then when a dipole is formed, obviously there is going to be a charge.

04:25 So this will be delta negative, and this will be delta positive.

04:34 And then obviously the delta positive side, it will induce a dipole into the neighboring molecules, and the delta positive side will be attracted to the delta negative side.

04:47 The larger an electron cloud, meaning the more electrons a molecule has, the more polarizable the atom is on a non -polar molecule and the greater the dispersion forces.

04:59 The greater the surface area of an atom or the non -polar molecule, the greater the dispersion area.

05:05 So we've already, there's two factors that affect the dispersion forces, electron cloud and surface area.

05:12 The larger they are, the greater the dispersion forces.

05:15 Strength increases with the increasing electrons and larger atoms because the electron, so you might be asking yourself, why does a larger electron cloud lead to greater dispersion forces? this is because the electron clouds are easier to distort if they are larger.

05:29 They're more polarizable to other atoms.

05:33 And with larger molecules, we know greater dispersion forces.

05:37 So the boiling point will also increase as well.

05:39 That's something important to keep into mind.

05:41 Moving on to dipole -dipole forces, this is a pretty straightforward one.

05:45 It's just a dipole interacting with a dipole.

05:48 All polar molecules have permanent dipoles.

05:50 And dipole -diple forces occur upon the positive end of one dipole as we can see here.

06:03 The positive end of one permanent dipole is attractive to the negative end of another permanent dipole.

06:10 Increasing dipole moment increases the polarity, so boiling point increases as well because there are stronger interactions, so more energy is required.

06:19 That's pretty straightforward...

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