the last topic for chapter one is the polarity of molecules in order to determine the polarity we will have to know the shape of the molecules and we have explained previously that in order to determine the shape of the molecule we have to start with the Louis structure so Louis structure is the basic for doing all this okay so let's start with some simple molecules first let's take a look at hydrogen H2 in hydrogen molecule we have hydrogen hydrogen bond and they are made I mean these two atoms are identical so hydrogen hydrogen bond will be a nonpolar coent Bond the molecule will be nonpolar molecule okay next for HCL we know chlorine is more electron negative than hydrogen so chlorine will draw more electron away from hydrogen the molecule has a dipole moment that is pointing to the direction of ch as a result HCL bond is a polar bond and the molecule HCL is a polar molecule okay next molecule we will look at BF3 we've seen this molecule before in Louis structures Boron is electron deficient it doesn't satisfy the octy set we have three flooring around the Boron and the shape of the molecule is trigonal plane right so we know the Florine atom is the most electronegative element so the Boron Florine Bond should be polar bound with the dipole moment pointing to the direction of Florine we have three polar bonds so here are the three bonds the dipole moments in order to determine the polarity of the molecule we have to make a sum of this dipole moment okay so what we are going to do is draw parallel Lin lines here along the edge of the arrow the parallel line that are will be parallel to the other dipole moment and we are getting the sum of the vectors okay the sum of dipole moment dipole moments are vectors they have directions so we get the sum of these vectors and we've seen that this blue arrow this blue arrow is the sum of the top arrow and the left Arrow while the blue arrow and the third arrow on the right hand side they are opposite in direction and they will be equal in strength so they are going to cancel each other as a result BF3 molecule will be a nonpolar molecule so this is the example that we have polar bonds but due to the symmetry of the molecule due to the shape of the molecule it's a nonpolar molecule the next example we will look at is CO2 we've seen the structure and we know it's a linear molecule carbon oxygen bonds are polar because oxygen is more electr negative than carbon the molecule is linear so these two dipole moments will be pointing to the opposite side and they are are equal in length so they cancel each other okay this is another example of nonpolar molecule with polar bonds next hch this is the formal alide in the Lou structure we have carbon oxygen double bond the shape of the molecule is is trigonal planer the carbon oxygen double bond will be polar okay dipole moment pointing to the direction of oxygen the carbon atom and the hydrogen atom have similar electr negativity in organic chemistry we would refer carbon hydrogen bond as a nonpolar Bond okay so we have only one dipo moment in this case we have polar bond and because the dipo moment would not cancel this molecule is a polar molecule next example CH H2 cl2 d chloro methane if you draw the Lou structure you see we have the central carbon atom with two chlorine atoms and two hydrogen atoms attached to it the molecule will be in the tetraedron shape okay the carbon chlorine bond will be polar the carbon hydrogen bonds will be nonpolar for the two c c polar bond the sum of the dipo moment is like that so we have polar bonds in this molecule and we also have a polar molecule because the blue arrow there will not cancel with any other dipole moment but for C cl4 which is quite similar to the previous case in structure tetraedron shape okay with four chlorines attached to the central carbon atom but now we have four polar bonds and if we do the sum of these vectors you've seen the first blue arrow and the second blue arrow they are pointing to exact the opposite direction and they will be equal in length so they are going to cancel each other we have polar bonds in the molecule but the molecule is nonpolar due to the shape of the molecule okay so I hope these examples will give you some idea to how to determine the polarity of the molecule okay you always have to start from drawing the Louis structure then get the shape of the molecule then determine if we have polar or nonpolar bonds will the dipo moment cancel each other or not all right we will do well I will leave this as homework for you to try it the first one is CH cl3 TR chloro method or we also call it chlorop form second n minus we've seen this example before you saw the Louis structure you saw the resonance structures now you need to to determine if this is a polar ion or nonpolar ion and the last example is s O3 sulfur trioxide okay also determine the polarity of the molecule