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Polar and Nonpolar Molecules

Jun 03, 2021
In this video we're going to talk about how to tell if a molecule is

polar

or non

polar

, but first we need to understand what it means for something to be pulling, so what I'm going to do is draw four objects and I want you to determine which of these four objects is polarized. So how would you describe these four objects? Let's start with the one on the top left. This object has positive and negative charges. In general, this object is neutral. You could describe this object as. an ion has a net positive charge this can be described as a negatively charged ion has a net negative charge the last object is generally neutral however it is polarized and the reason it is polarized is because one side is positive the other side is negative and basically a polar molecule has that characteristic, one part has a positive charge and the other part has a negative charge, so let me give you an example of a polar molecule.
polar and nonpolar molecules
Hydrofluoric acid is a polar molecule. If we draw the structure, there is only one. The bond between hydrogen and fluorine and fluorine is highly electronegative, it has an electronegativity value of 4.0 for hydrogen, it is 2.1, so because fluorine is more electronegative than hydrogen, it will attract electrons towards itself, so fluorine will acquire a partial negative charge and hydrogen is If we are deficient in electrons, we will acquire a partial positive charge, so if we were to draw the molecule, this would be hydrogen and this would be fluorine. Fluorine is larger than hydrogen, but Floyd has a negative charge relative to hydrogen and hydrogen has a positive charge. charge, so this molecule is polar because one side is positive and the other side is negative.
polar and nonpolar molecules

More Interesting Facts About,

polar and nonpolar molecules...

Now let's make a distinction between polar

molecules

and non-polar

molecules

. In polar molecules, electrons are shared unequally. In

nonpolar

molecules, the exchange of electrons is relatively equal. In the case of fluorine from hydrofluoric acid, although hydrogen and fluorine share electrons, they do not share them equally, which is why fluorine has a partial negative charge, it attracts electrons to itself and hydrogen has a partial positive charge, so that basically we have this image. one side is positive and the other side of the molecule is negative which makes the polar hydrogen gas HF non-polar because the two atoms in the molecule are the same, the electrons are shared equally, so if you were to draw you wouldn't have a positive region and a negative region they are generally just neutral and therefore non-polar molecules don't have that charge separation like we see in polar molecules, so whenever you see a molecule that is made up of a type of element, it is automatically non-polar, so let's go over some rules because normally, if you're studying for an exam, you need to quickly determine if a molecule is polar or not, so let's go over non-polar molecules.
polar and nonpolar molecules
Molecules that contain only one type of element are automatically non-polar, like h2 + 2 O. 2 F 2 BR 2 CL 2 I 2 if you see these you automatically know it's non-polar now the second thing to look out for is hydrocarbons , so if you have a molecule that contains only carbon and hydrogen, like methane, ethane, propane and things like that. Thus the hydrogen bond of non-polar carbon is automatically non-polar for a bond to be polar the difference in negativity of choice between the two elements in that bond has to be greater than or equal to 0.5 or more the electronegativity of carbon is approximately 2.5 and for hydrogen it is 2.1 then the difference in electronegativity between these two elements is point 4 which makes the bond non-polar so hydrocarbons i.e. molecules contain only carbon and hydrogen are non-polar, so just knowing this, this is half the battle, now the next thing we need to consider is the geometry of the molecule because that can make the difference between the molecule being polar or non-polar, so So let me give you some examples of carbon tetrafluoride.
polar and nonpolar molecules
Would you say this molecule is polar or

nonpolar

? Well, first before we discuss the polarity of the molecule, let's talk about polarity. of the bond is the bond carbon fluorine polar or non-polar the electronegativity of carbon is 2 point 5 and for fluorine it is 4.0 so we have a difference in 1.5 which means that the bond is polar so not the molecule but the bond but now what? what's happening? The molecule is the molecule as a whole, is it a polar or non-polar molecule? So we need to draw it to have four fluorine atoms and the molecular geometry is tetrahedral, so the bond angles are not 90 but 109.5, so technically it is a three-dimensional shape. is not a 2D shape, now you need to draw something known as a dipole moment.
The dipole moment is basically seen as an arrow that points starting from the atom with the partial positive charge but points towards the atom with the partial negative charge, so the four arrows Look like this, notice that they all point in opposite directions, these arrows are oriented in such a way that they all cancel, so the dipole moment of this molecule is zero, so all the dipole moments cancel, the molecule as a whole is nonpolar. but the bonds in this molecule are polar, so these are things you need to keep in mind now. What happen with the water?
Is water polar or non-polar? Well, let's first analyze the bond: OAH bond, hydrogen has an electronegativity value of 2.1 and oxygen is 3.5, so the electronegativity difference is 1.4, it is greater than 0.5, which means that water has polar bonds. Now we need to look at the geometry of water's oxygen to form two bonds and it has two lone pairs and because it is more electronegative it will have a partial negative hydrogen charge. it will have a partial positive charge and if we draw the dipole moments that will point towards the more electronegative oxygen atom, it will look like this, so notice that we have a net dipole moment in this molecule and as a result, the molecule is now polar. let's talk about why the two arrows don't cancel and hopefully you took a physics course and you understand how to add vectors, but let's draw two arrows that look like this, let's call this arrow an arrow until the first arrow has an goes to the right and the y component going up, the second arrow has an excellent point going to the left and the y component going up, notice that the they do it. t cancel and therefore are additive, so the water in that diaper has a momentum going towards the oxygen atom, so this side is positive and the top has a partial negative charge, so that the dipole moment goes towards the partial negative oxygen atom, which creates water is polar, so molecules that have a net dipole moment are polar and non-polar molecules generally have a dipole moment of zero, so have this into account.
Now let's go over two more examples of carbon dioxide and sulfur dioxide, which of these two molecules is polar and which is non-polar, feel free to pause the video and work on this example. Now the best thing you can do is draw the Lewis structure. Carbon dioxide is a linear molecule. Sulfur dioxide has a bent shape. Now both carbon and sulfur have an electronegativity value of 2.5 and We know that oxygen has an electronegativity value of 3.5, so in both cases the carbon-oxygen bond and the sulfur-oxygen bond are polar because they both contain a difference in of 1, so they both have polar bonds.
Now let's draw the partial charges in both oxygen cases. will carry a partial negative charge and carbon and sulfur will have a partial positive charge because they are less electronegative than oxygen. Now let's draw the dipole moments in the case of carbon dioxide. Notice that the dipole moments are opposite to each other, so they cancel out completely, so you have a dipole moment of zero, which means that CO2 is a non-polar molecule even though it has polar bonds. Now, in the case of sulfur dioxide, the dipole moments do not completely cancel the X components, they cancel because they are opposite. each other, but the Y components of the dipole moment are in the same direction, so they add up, which means that that type of moment for this structure is in a negative Y direction based on the way it is drawn and so So much so, because sulfur dioxide has a dipole moment that is greater than zero, we do not know what the number is, but you can look it up because it is not equal to zero, this molecule is polar and now you know how to know if a molecule is polar or not polar. step one look for any element or look for any molecule that contains only one type of element like h2 and 202 if they only have one type of element it is automatically nonpolar step 2 look for any hydrocarbon so if you see a molecule that has only carbon and hydrogen it is non polar step 3 for other molecules that are made up of different elements like hf h2o co2 the best thing to do is to draw the lewis structure and then see if the dipole moments cancel or if there is a net dipole moment and also check the bonds to make sure they're also polar and that's all I have for this video.
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