in this video I I'll will talk about polarity of molecules but before we talk about polarity of molecules let's look at polarity of individual bonds there are two types of calent bonds we have non-polar calent bonds and polar calent bonds in a non-polar coent Bond the electrons are shared evenly and this is a bond between the same or identical non-metals example of a non-polar coent bond is the molecule hydrogen which consists of two hydrogen atoms the line that's shown between the two hydrogens with the two dots represents the calent bond and the two dots are the electrons that are shared between the hydrogens the red line or the red outline represents the electron cloud that results from the sharing of these two electrons notice how the electron cloud the electron or the electron density is distributed evenly around these two hydrogens and that's a very representative of non-polar calent Bonds in a polar calent bond however the electrons are not shared evenly and that's because the electrons are between are shared between two different non-metals example of a polar calent bond is hydrogen fluoride these two electrons right here that are sh shown on on the line represent the sh the bonding electrons the other dots in blue are the L Pairs and then the red outline is the electron cloud or the electron density distribution and notice how there's a lot more electron density on Florine and a lot less on hydrogen and why is that because Florine tends to pull the bonding electrons closer to itself which leaves hydrogen electron four so how do we determine which atom will pull the electrons CL closer to itself and will get more electron density and which atom will have less electron density we will use a periodic trend called electro negativity the abbreviation for that is en n and the definition for electro negativity is the ability or the tendency of an atom to attract shared electrons towards itself and here's the trend that you need to memorize as we moved from left to right on the periodic table imagine this is a periodic table as we move from left to right electr negativity increases as we move from bottom to top electro negativity also increases in fact both arrows Point towards Florine which is the most electronegative atom and I'll show you a periodic table here's Florine we're disregarding group eight elements the noral gases do not participate in in reactions we don't have to worry about them as we move from left to right we get closer to Florine electr negativity of atoms increases as we move from bottom to top again electro negativity of atoms increases Let's do an exercise which of these two have higher Electro negativities you have to find these on the periodic table and figure out which are closer to Florine so we're comparing first oxygen versus selenium here's oxygen here's selenium both are in group six oxygen however is closer to Florine and that's why it's more electronegative Boron versus nitrogen Boron and nitrogen are both in Period two nitrogen is closer to Florine it's more electronegative cium versus phosphorus here's cium in group one period six and here's phosphorus it's in group five period three these are not in the same groups they're not in the same periods but they're so far away from each other one is definitely closer to Florine versus the other phosphorus is closer to Florine cesium is much further away from Florine therefore phosphorus is more electronegative we can show Bond polarity using two different ways one method is by using partial charges and these are shown using the Greek symbol called Delta Delta plus is used for Less electronegative atoms Delta minus is used for more electronegative atoms here's an example of a polar bond hydrogen fluoride hydrogen is less electronegative repl the Delta plus symbol above hydrogen Florine is more electronegative it gets the Delta minus symbol oxygen and carbon another polar coent bond oxygen is more electronegative we place the Delta minus above it carbon is less electronegative we place the Delta plus above it phosphorus versus chlorine phosphorus is less electronegative it gets the Delta plus charge chlorine is more electronegative Delta minus and then last example sodium iodide this is not a Bond because it consists of a metal and a nonmetal this is ionic and instead of partial charges we have full charges there's a full positive charge and a full negative charge on the iodine so the reason why I included this here is I wanted to show you the difference between partial charges that are part of coent bonds and full charges that are part of ionic bonds now the second way we can show polarity is using a polarity arrow and the way we draw a polarity arrow is we start by drawing a positive sign and then we extend that into an arrow and the positive sign is above the less electronegative atom the arrow points towards the more electronegative atom let's use the same examples that we saw earlier hydrogen fluoride hydrogen is less Electro negative we draw the positive sign above it and then we extend the arrow towards Florine which is the more electr negative atom now if you have multiple coent Bonds in the moment Mo such as in boron Tri chloride then you have to draw multiple polarity arrows when you draw these arrows keep in mind they have to be parallel to the calent bonds in this example Boron is a less electronegative chlorine is more electronegative so all the arrows start at Boron and then they Point towards the chlorines which are the outer atoms and again try to draw these arrows parallel to the calent bonds another example is water it has two polar bonds hydrogen is less Electro negative oxygen is more Electro negative the arrow starts at hydrogen and points towards the more Electro negative oxygen and again I'm drawing these parallel to the calent bonds ammonia another example there are a total of three calent bonds hydrogen is less electronegative than nitrogen the arrow starts at all the hydrogens and they Point towards the central nitrogen now if you were asked to do the same thing but with partial charges for ammonia you would include three partial plus charges above each hydrogen so one partial charge above each hydrogen that's total of three and you include one partial negative charge above nitrogen so now that you have this information let's do the following example identify these molecules or these types of bonds as Polar calent non-polar calent or ionic first example are two hydrogens um these are identical excuse me identical non-metals and therefore the bond between them is nonpolar clcl identical non-metals the N the bond between them is also non-polar hbr these are two different nonmetals the bond is polar HCL two different nonmetals polar coent bond na a this is a metal and a non-metal ionic bond M mg o metal non-metal ionic bond so finally now that we know how to identify polar bonds versus non-polar bonds now we're ready to talk about the overall polarity of molecules these are the three different steps you have to take when you identify the overall polarity of molecules the first step is to draw the molecule in its correct shape this means that first you draw the Lis structure for the molecule and then you take it a step further and you redraw the low structure so that it reflects the corre cor Bond angles once you have the shape drawing and if you have any questions about this look at the previous video where I explain exactly how to come up with shape drawings for molecules Second Step you need to draw the polarity arrows across all the polar bonds in the shape drawing and then the third step is once you have these polarity arrows imagine that there are forces add them up and if these forces cancel out then the molecu is non-polar if the forces do not cancel out then the molecule is polar let's do some examples so you get an idea of what I'm talking about let's look at carbon dioxide carbon dioxide has a linear molecular geometry carbon is Central the oxygen are the outer atoms and this is the correct shape drawing the second step is to add the polarity arrows carbon is less electronegative than oxygen so we start the positive sign at Carbon and we extend the arrow towards oxygen do the same thing on the other side now imagine that these oxygens are pulling on the central carbon the right oxygen is pulling on the central carbon in the right direction the left oxygen is pulling on the central Carbon on in the left Direction so one uh pulls to the right one pull to the left with equal force the question is would the central C carbon move or would the central carbon stay in one place since the forces are in opposite directions and they're equal to each other then carbon will not move and overall these forces cancel each other out and the molecule is non-polar now I want to warn you that these vectors or these polar arrows do not represent forces they actually represent magnetic moments I'm assuming that you haven't taken physics and you probably haven't talked much you haven't learned much about magnetism that's why I want you to imagine that these are forces they're not really forces there's no pushing or pulling going on here but if you think of them as forces and if you ask yourself do these forces cause the central atom to move or not then it's much easier to predict polarity of molecules this is think of this is a shortcut so overall if the forces cause the central atom to move then the molecule is polar if the central atom doesn't move then the molecule is nonpolar let's look at the second example H2O once you draw the low structure and then you draw the shape drawing you end up with bent molecular geometry oxygen is Central hydrogen are outer hydrogen are less electronegative and that's why we start the arrow at hydrogen and we point it towards oxygen parallel to the calent bonds and then ask yourself the following question if these hydrogens are pushing on the oxygen would they cause the oxygen to move or would the oxygen stay in one place the oxygen will actually move and it will move up in the upwards Direction the mo of the central atom is shown is a thicker Arrow like that and that's called a net dipole so if there is a net dipole in the molecule and the central atom moves as a result of the pushing or pulling of the outer atoms then the molecule is polar there's a net dipole let's look at ammonia NH3 the shape drawing is here this is trigonal pyramidal molecular geometry the hydrogen atoms are less negative and they push on the nitrogen and they push the nitrogen in upward Direction here's the direction of the net dipole again I'm showing this is a thicker Arrow this is different from the arrows that we use for reactions or for from polarity arrows overall the molecule is polar because the central atom moves upwards BF3 Boron is Central Florine are the outer atoms the molecular geometry or the correct shape drawing is trigonal planer Boron is less electronegative Florin are more electronegative we show the arrows pointing towards Florine this is a little tricky to see but if these were flines that are pulling on the Boron because they're symmetrically positioned around the Boron the Boron will not move so anytime there's symmetrical forces this could be in trial planer geometry or tetrahedral geometry or linear geometry like we saw here symmetry if there's symmetry around the central atom that results in a non-polar molecule the forces cancel out and there's no net dipole ch2o this is the molecule for Malahide carbon is Central because carbon is always Central and then oxygen and the two hydrogen are outer atoms carbon oxygen bond is polar carbon is less electron negative oxygen is more electronegative so the arrow points towards oxygen hydrogen versus car hydrogen is less electronegative carbon is more electronegative the arrows Point towards carbon so let's see what's going on with carbon there are two forces from hydrogens that push carbon upwards and there's one force from oxygen that pulls carbon also upwards so overall carbon will move up and the net dipole moment points up this is definitely a polar molecule let's look at another molecule methane which has tetrahedral shape t hro geometry there's symmetry here all the arrows Point towards carbon in a symmetric fashion and that's why carbon doesn't move it's non-polar molecule ch3f you can place the Florine up down to the left it doesn't matter either way you draw the molecule as long as you have a tetrahedral shape you notice that there is a net D dipole moment that pulls the molecule towards wherever you replace the Florine I chose to put the Florine up so in this case the hydrogen are pushing the carbon atom up Florine is pulling it up the net dipole points up if you were to put the floor in here on the right you notice that the net dipole points to the right either way the molecule is polar because there's a net dipo moment hcn is another polar molecule carbon is Central nitrogen and hydrogen are outer atoms the linear the geometry is linear carbon nitrogen bond is polar and the bond points the arrow points towards nitrogen HC is polar the arrow points towards carbon overall both of the arrows point to the right there's a net dipole moment making this molecule polar carbon dulfi has a linear geometry this is another one of the symmetric molecules the carbon sulfur sulfur is slightly more electronegative than carbon so both of the arrows point away from carbon in opposite directions if you think of them as forces they cancel each other out resulting in a nonpolar Bond