in this video we're gonna talk about how to tell if a molecule is polar or nonpolar but first we need to understand what it means for something to be pulling and so what I'm gonna do is I'm gonna 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 upper left so this object has positive and negative charges so overall this object is neutral this object you could describe it as an ion it has a net positive charge this one you can describe it as a negatively charged ion it has a net negative charge the last object overall it's a neutral however it's polarized and the reason why it's polarized is because one side is positive the other side is negative and basically a polar molecule has that feature one part of it has a positive charge and the other part has a negative charge so let me give an example of a polar molecule hydrofluoric acid is a polar molecule if we draw the structure there's a single bond between hydrogen and fluorine and fluorine is highly electronegative it has an electronegativity value of 4.0 for hydrogen it's 2.1 and so because fluorine is more electronegative than hydrogen it's going to pull the electrons toward itself and so fluorine will acquire a partial negative charge and hydrogen is going to be electron deficient it's going to acquire a partial positive charge so if we were to draw the molecule this would be hydrogen and this would be fluorine fluorine is bigger than hydrogen but Floyd has a negative charge with respect to hydrogen and hydrogen has a positive charge and so this molecule is polar because one side is positive and the other side is negative now let's make a distinction between polar molecules and nonpolar molecules in polar molecules you have an unequal sharing of electrons in nonpolar molecules the sharing of electrons is relatively equal so in the case of hydrofluoric acid fluorine even though hydrogen and fluorine are sharing electrons they don't share equally so that's why fluorine has a partial negative charge it pulls the electrons toward itself and the hydrogen has a partial positive charge so basically we have this picture one side is positive and the other side of the molecule is negative make an HF polar hydrogen gas is nonpolar because the two atoms in the molecule are the same the electrons are shared equally and so if you were to draw a picture you don't have a positive and a negative region overall is simply just neutral and so nonpolar molecules they don't have that separation of charge as we see in polar molecules so anytime you see a molecule that is made up of one type of element it's automatically nonpolar so let's go over some rules because typically if you're studying for a test you need to quickly determine if a molecule is polar or not so let's go over the nonpolar molecules molecules that contain only one type of element are automatically nonpolar such as h2 + 2 O 2 F 2 BR 2 CL 2 I 2 if you see these automatically you know it's nonpolar now the second thing you need to watch out for are the hydrocarbons so if you have a molecule that contains only carbon and hydrogen such as methane ethane propane and things like that it's automatically nonpolar the carbon hydrogen bond nonpolar for a bond to be polar the election negativity difference between the two elements in that bond has to be greater than or equal to 0.5 or more the electronegativity of carbon is about 2.5 and for hydrogen its 2.1 so the electronegativity difference between these two elements is point 4 making the bond nonpolar so hydrocarbons that is molecules contain an only carbon and hydrogen are nonpolar so just by 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 of the molecule being polar or nonpolar so let me give you some examples carbon tetrafluoride would you say this molecule is polar or is it nonpolar well first before we analyze the polarity of the molecule let's talk about the polarity of the bond is the carbon fluorine bond polar or nonpolar the electronegativity of carbon is 2 point 5 and for fluorine it's 4.0 so we have an en difference of 1.5 which means that the bond is polar so not the molecule but the bond but now what about the molecule is the molecule as a whole is it a polar or nonpolar molecule so we need to draw it so we have four fluorine atoms and the molecular geometry for it is tetrahedral so the bond angles are not 90 but 109.5 so technically it's a 3d shape not a 2d shape now you need to draw something known as the dipole moment the dipole moment looks basically like an arrow that points starting from the atom with the partial positive charge but appoints towards the atom with the partial negative charge and so the four arrows will look like this notice that they all point in opposite directions these arrows are oriented in such a way that they all cancel out and so then that dipole moment for this molecule is zero so because all of the dipole moments cancel the molecule as a whole is nonpolar but the bonds in this molecule are polar so these are things you have to look out for now what about water is water polar or nonpolar well first let's analyze the bond the OAH bond hydrogen has an electronegativity value of 2.1 and for oxygen is 3.5 so the electronegativity difference is 1.4 it's greater than 0.5 which means that water has polar bonds now we need to analyze the geometry of h2o oxygen like to form two bonds and it has two lone pairs and because it's more electronegative it's going to have a partial negative charge hydrogen will have a partial positive charge and if we draw the dipole moments which will point towards the more electronegative oxygen atom it's going to look like this so notice that we have a net dipole moment in this molecule and so as a result the molecule is polar now let's talk about why the two arrows don't cancel and hopefully you took a course in physics and you understand how to add vectors but let's draw two arrows that look like this let's call this arrow one arrow to the first arrow has an X component that goes towards the right and the y component that goes up the second arrow has an excellent point going to the left and the y component going up notice that the X components they cancel because they're opposite to each other however the Y components they don't cancel and so they're additive thus water has in that diaper moment that goes towards the oxygen atom so this side is positive and the top part is it has a partial negative charge and so the dipole moment goes towards the partial negative oxygen atom making water polar so molecules that have a net dipole moment are polar and nonpolar molecules typically have a dipole moment of zero so keep that in mind now let's go over two more examples carbon dioxide and sulfur dioxide which of these two molecules is polar and which one is nonpolar feel free to pause the video and work on this example now the best thing to do is to draw the Lewis structure carbon dioxide is a linear molecule sulfur dioxide has a bent shape now both carbon and sulfur they both have an electronegativity value of 2.5 and we know oxygen has an en value of 3.5 so in both cases the carbon oxygen bond and the sulfur oxygen bond are both polar because they both contain an en difference of 1 so they both have polar bonds now let's draw the partial charges in both cases oxygen will carry a negative partial charge and carbon and sulfur will have a partial positive charge because they're less electronegative than oxygen now let's draw the dipole moments in the case of carbon dioxide notice that the dipole moments they're opposite to each other so they completely cancel so this has 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're opposite to each other but the Y components of the dipole moment they're in the same direction so they add up which means that then that type of moment for this structure is in a negative Y direction based on the way it's drawn and so because sulfur dioxide has a dipole moment that is greater than zero we don't know what the number is but you can look it up because it's not equal to zero this molecule is polar and so now you know how to tell if a molecule is polar or nonpolar so step one look out for any elements or look out for any molecules that contain only one type of element like h2 and 202 if they only have one type of element it's automatically nonpolar step 2 look out for any hydrocarbons so if you see a molecule that has only carbon and hydrogen it's nonpolar step 3 for other molecules that are composed 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 if they cancel or if there's a net dipole moment and also check the bonds to make sure the bonds are polar as well and so that's all I got for this video for those of you who like it feel free to subscribe to this channel and I'm gonna post some videos in the description section below feel free take a look at that when you get a chance thanks again for watching