ShmoopTube

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Here’s your Shmoop du jour, brought to you by Thanksgiving Dinner, bringing atoms together [A thanksgiving dinner on a table and atoms drinking wine]

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since 13.82 billion BC!

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…Or maybe that was intermolecular forces….

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Here’s our question…

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Which of the following correctly represents the order of intermolecular forces of attraction

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(IMFs) from weakest to strongest?

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And here are our potential answers…

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To answer this question, we first have to understand how each of these intermolecular [Hydrogen bond, dipole dipole and london dispersion having dinner]

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forces of attraction work.

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That might mean watching a few atom-based romcoms… you know, like Chargeless in Seattle,

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or When Harry Met Electron… [Man with atom as a face meets girl with electron as a face]

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Or it might just mean watching the rest of this video.

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The forces listed in the question are dipole-dipole forces, London Dispersion forces, and hydrogen

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bonding.

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And since we don't have our copy of Bridget Jones Dipole Diary on us, let's just go through [Man in videostore picking a DVD]

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them one by one…

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Starting with dipole-dipole forces.

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When we’re talking about dipoles, we’re actually talking about two important areas

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of small electric charge on a molecule. [Electric charges]

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When a bond exists in a molecule between two atoms with very different electronegativities,

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the atom with the higher electronegativity hogs a disproportionate amount of electrons. [Atom grabs electronegativity at a table]

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Kind of like your cat’s idea of “sharing” furniture space.

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Atoms that control more electrons in a bond become more negative in charge.

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This leaves the other atom in the bond with a slight positive charge.

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Dipole-dipole interactions occur when the slight negative charge of an atom in a dipole [negative charges of a molecule circled]

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is attracted to the slight positive charge of an atom in a dipole in a different molecule.

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Which means dipole-dipole interactions attract the two molecules together. [Molecules attract to dipole dipole magnet]

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Dipole-dipole interactions are reasonably strong intermolecular forces, but the strength

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varies depending on the intensity of the dipole. [Dipoles with flexed biceps]

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The bigger the difference in electronegativities, the stronger the interaction.

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Guess what has a really low electronegativity?

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Hydrogen. [Arrow points to hydrogen]

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And guess what has a really high electronegativity?

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…Well, lots of things, but most commonly Oxygen, Nitrogen, and Fluorine.

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And because we're generous 'round these parts, we'll give you three guesses as to what a [Man holding a sign saying 3 guesses]

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dipole-dipole interaction in a molecule with a bond between Oxygen, Nitrogen, or Fluorine,

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and a Hydrogen is called…

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Yup the answer to our super tricky question is hydrogen bonding. [Hydrogen atoms bonding and explosion occurs]

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A hydrogen bond is a particularly strong dipole-dipole interaction, because the difference in electronegativity

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is so large between Hydrogen and elements like Oxygen or Nitrogen.

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This means that in general, hydrogen bonds will be stronger than general dipole-dipole

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interactions; however, the two interactions are similar in strength. [Hands touch each other]

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Since hydrogen bonds and dipole-dipole interactions are similar in strength, London dispersion [Hydrogen bonds and dipole dipole on a see-saw]

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forces must be either stronger than both or weaker than both.

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So where do they fall?

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Well, London dispersion forces are actually a pretty weak force, because they result from

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a property of the electron cloud of a molecule known as its polarizability. [Electron cloud and weather reporter man appears]

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That's just a fancy way of saying that the electrons can move around to make little tiny

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dipoles….giggity…. [electrons create a dipole in an electron cloud]

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This happens if more electrons end up on one side of a molecule for a short period of time.

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A good way to compare these forces comes, like many good things, from the kitchen. [Selection of food in a kitchen]

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London Dispersion Forces are best approximated by the forces holding together wet spaghetti

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noodles, whereas hydrogen bonds are like the forces holding together a single block of [Man holding large blocks of ice]

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ice.

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You can pull the spaghetti apart with your hands but good luck trying that with ice.

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Since London Dispersion Forces are so weak, the answer must be C.

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But just because London Dispersion Forces are weak, doesn't mean they can't find love. [London Dispersion Force working out in a gym]

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Four Weddings and a London Dispersion Funeral….Coming soon, to a theatre near you.

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