ShmoopTube

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Here’s your Shmoop du jour, brought to you by dipoles.

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Because we're just dying to pole you in to this video. [Tablet showing a shmoop video]

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Here’s the question we have to tackle:

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Which of the following molecules has a dipole moment of zero?

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And here are our potential answers…

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There are two steps needed to figure out the dipole moment of a molecule. [Woman taking two steps on a piece of furniture]

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Step one: figure out which bonds have dipoles, and in what direction.

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And step two: cancel out dipoles pointing in opposite directions. [Hands removing dipoles]

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Let’s jump right into step one. [Man jumps into swimming pool]

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A dipole is just an unequal sharing of electrons in a bond.

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Kind of like how our older brother “shares” things with us… [Younger brother trying to grab a teddy off older brother]

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Dipoles occur in a bond between an atom with a high electronegativity and an atom with

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a lower electronegativity, because atoms with high electronegativity are very selfish. [Atom with high electronegativity]

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Just like our older brother, except he's less selfish over electrons, and more over basically everything else

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in the world… [Brothers fighting over a toy car]

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When we have an electronegative atom in a bond, we draw an arrow along the bond pointing

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to the more electronegative atom, which calls them out for hogging the electrons.

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Why be subtle, right?

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Anyway, this arrow is the dipole of the bond. [Arrow showing dipole of a bond]

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And how do we identify electronegative atoms in a bond?

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We look at the handy-dandy periodic table, which is essentially Facebook for the elements. [Scientist studying the periodic table on a computer]

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Electronegativity follows a regular trend on the periodic table, excluding the Noble

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gases, because they can’t be bothered to follow the trends of the common folk.

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As we move right or up along the periodic table, electronegativity increases, with Fluorine [Arrows point to Fluorine on a periodic table]

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being the most electronegative atom.

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And if we're comparing two atoms, the atom further to the right, or further up on the

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periodic table is more electronegative.

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This means the dipole of a bond between those two atoms will point to the atom further up

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or further right on the periodic table.

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Okay.

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Phew.

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So.

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…What was the question asking again? Oh right.

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Now let’s draw our dipole arrows on our molecules. [Girl drawing arrows on a molecule]

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Our molecules without the dipole arrows will look something like this…

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Let’s go through them one by one and draw in our dipoles.

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First we have H2O. [H2O in chemical form]

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The bonds in this molecule are between Hydrogen and Oxygen.

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Oxygen is much further right on the periodic table than Hydrogen, so we know that it's

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more electronegative.

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And if we draw in our bond dipoles....

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Any dipoles pointing in opposite directions will cancel. [Dipoles drawn on a H2O molecule]

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The dipoles in this molecule point up left and up right.

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The left and right cancel, but the up parts add, giving us a leftover dipole.

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So answer A is off the table. [H2O answer crossed out]

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What about answer B, CO2?

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This molecule has bonds between Carbon and Oxygen.

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Oxygen is much further right than Carbon on the periodic table so it's more electronegative [Periodic table showing oxygen and carbon]

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and our dipoles will point towards oxygen.

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One dipole points left and one points right, which means that no one wins this tug of war. [Dipoles pointing in opposite directions]

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And if there's no leftover dipole, then yup, this looks like our answer…but let's check [Two boys in a tug of war]

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out our other molecules, just for fun.

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Because what could be more fun than looking at more dipole moments?

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Applying the same logic to the next two molecules, we see that SOCl2 has dipoles pointing towards [SOCl2 molecule shown with dipoles pointing towards oxygen and chlorine]

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oxygen and chlorine, like so:

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The bond dipoles of this molecule all point in different directions, but nothing points

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towards the lone pair.

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This means there will be a net arrow pointing opposite that direction… [Finger points to dipole arrow]

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And that means this definitely isn't our answer.

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Which brings us to our last competitor, D, CHCl3. [Letter D in a boxing ring]

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The molecule looks something like this:

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Chlorine is much more electronegative than carbon, and hydrogen has a very similar electronegativity

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to carbon, so our bond dipoles will look like this: [CHCl3 molecule]

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Nice.

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Our carbon-hydrogen bond will have no dipole, and our carbon-chlorine bonds will have dipoles

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pointing to chlorine.

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This gives us a net dipole that looks something like this: [CHCl3 molecule with dipoles pointing to chlorine]

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And remember when we started this question approximately twenty years ago, that we were

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looking for a molecule with NO dipole.

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So this is not the answer.

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So that means B is most definitely our answer.

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But hey, what better way to spend your time than with molecules? [Scientist using a pipette to transfer blue substance into a flask]

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….Point taken.

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