all right so turns out in covalent bonds some atoms do not share as well as others we call this tendency to not share well electronegativity and elect differences in electronegativity can result in either I can result in polar covalent bonds so let's look at types or flavors of covalent bond we'll talk about polar and nonpolar so electronegativity is the tendency for electrons which are negatively charged to be attracted to certain nuclei of atoms and some atoms are electron hogs these really really want those electrons and our electron hog is going to be oxygen oxygen really likes electrons and it does not share well and of course we see that within our sponge the other atoms that doesn't share well is nitrogen so nitrogen is going to be our this is where you have to see if you can figure out what I'm trying to draw for lack of a better picture this is our electron eagle so the point is oxygen and nitrogen do not share well if you imagine that this the covalent bond is like a tug of war between the two atoms involved these guys are the 350 pound linebackers they are going to have an advantage in terms of holding onto the shared electron versus a different type of atom that they're sharing with so what does that look like and these when these guys are with a less electronegative atom in the bond the result is going to be a polar covalent bond and for some reason I think people have a hard time at that term polar and it's not meant to be confusing or complicated so let's talk about first of all what the word for means and let's look at a really classic example of a polar molecule that are polar bonds in it and let's look at water so first of all polar as in poles of a magnet it means it two sides are opposite of each other or two sides are different from each other so the two sides of the magnet you have a north and south of the magnet in a polar bond the two sides of the bonds are different from each other and that even changes the shape of the molecules but we'll worry about that in a minute okay oxygen we're going to form a water molecule because water hugely important to living things and it is a polar molecule and you really have to know that like a lot of what we talk about from now on out is based on this idea so water we know is formed from one hydrogen start to hydrogen atoms and one oxygen atom and these three are bound together with covalent bond oxygen atomic number is eight hydrogen's atomic number is one so first question is how many total electrons and then the next question is how many valence electrons you've already done this with both of these guys so hopefully this doesn't take you very long oxygen has eight hydrogen has one electron oxygen you can put two of those electrons in the first shell so it has six valence electrons hydrogen can fit one in a per shell so it has one valence electron I'm going to stick three atoms together and your main normal how do I do this like what I do you know hydrogen here and hydrogen here and then an oxygen here like without work well let's think about that for a second hydrogen we know has one electron and this hydrogen has one electron and oxygen has six five six so I know the whole point of this line it represents shared electrons right well here this guy's sharing electron in this case you're an electron okay that works right that way everybody gets their full outer shell everybody gets two okay well what about oxygen over here these electrons are already committed to a bond oxygen isn't going to start sharing its two electrons with hydrogen I didn't eat any more anyway in this arrangement and oxygen isn't going to share two electrons when it's not getting anything back hydrogen can't be in the middle of this molecule so you have one electron to share the only atom that has more than one electron to share in this scenario is oxygen so let's put oxygen in the middle and see what happens there so I get six one two three four five six both of my hydrogens get one this works better so the hydrogen over here gets the share oxygens one the hydrogen over here gets the share oxygens one and the oxygen gets the share with both of the hydrogens and do some counting of electron goes in each of these circles and make sure everybody has their full set at the islands electron what they should and then we're going to even further simplify this by drawing our lines which represent two shared electrons so let's let's not forget about those yet let's draw the electron onto this line and I said oxygen is an electron hog so these electrons are going to spend more time next to the oxygen than they do next to the hydrogen some becomes thirds are up here electrons have a negative charge what does that mean to this oxygen it means that it ends up being slightly negative has a slightly negative charge not as much as an ion what about these hydrogen's so remember the whole point of it being a non charged atom was we said I know that the atomic number equals the number of protons so there's one proton at the nucleus and the nucleus of these atoms and they have positive charges right and the negative electron would counterbalance that so it end up with no charge but now it's negative charges hanging out over here so these guys end up being slightly positive in terms of their chemical charge and we can designate that so the oxygen will draw this little symbol here with a negative sign next to it this symbol of the Greek letter Delta lower case Delta and it just means partial partial charge and it's a partial negative that's the important part the negative rate and both of these hydrogen's are going to have a partial positive charge why is this a polar molecule again because I said polar just means the two sides of a molecule are different so I have one side of this molecule that is slightly negative and another side that is slightly positive and we'll spend the whole chapter talking about water and this property here that means that water tends to be sticky it these water molecules are going to stick to each other move we'll look at that in more detail later so things that makes all the water also going to be polar okay there's even a simpler way I can give you something that hey all you have to do memorize and recognize in living things we're going to have four commonly occurring polar covalent bonds you should be able to work this out but you know if it's simpler you can memorize it and I really rather you not memorize it but polar covalent bond okay so let's go back to our very electronegative atoms and hopefully you remember like the one we just showed up there one was oxygen electron hog right so oxygen is going to be involved in two of the four polar covalent bonds and the other electron eagle was nitrogen so it's going to be involved in the other two what are other molecules that we find in living things in the world for now we'll leave out all six we'll just look at the focus on the four so CH on right carbon and hydrogen oxygen nitrogen so these guys are going to be the three hundred-pound linebackers they need to be in a covalent bond with something that's you know a 50-pound kid or sort of a typical you know 150 pound individual and so if I have a bond between oxygen and carbon or bond between oxygen and hydrogen these electrons that are represented by this little line are going to spend more time next to the oxygen and the less time next to the carbon and hydrogen so oxygen ends up being slightly partially negative in both cases and these two end up being slightly positive rather than give you these two wands I think you can work it out follow the pattern that you see up here so what are the other two atoms that are going to be bound to nitrogen and what are going to be the partial charges on nitrogen and the other two atoms right there's a pattern I think you can see it figure out what two atoms belong here and also the charges the partial charges on both nitrogen and the other two atoms so that's another way that you can just keep track of if I see these they're going to be polar they're not going to share very equally and polar things are going to mix well with water like dissolves like maybe four dot before soap or things in Excel or things um okay so if it's not a polar covalent bond it's going to be a nonpolar covalent bond this is where atoms share equally there's going to be no difference between the two sides of the bond and one one way you can get atoms to share equally is by having the same electorate same atom on both sides of the bond so if I have a double bond between two oxygen sure they're both three hundred-pound linebackers but they're you know they're both fighting against each other so this molecule is a non-polar molecule B both of these bonds are nonpolar bonds same as if I put two hydrogen's together and you can follow that pattern the other nonpolar bonds we see a lot carbon-carbon shared really nicely so it will share well with itself right we just talked about that it also shares well with hydrogen so these in particular are nonpolar bonds I mean anything that's not one of these four bonds are going to be usually non-polar bond and we see these bonds a lot in fat and fat don't mix well with water nonpolar things think fatty ie don't mix with water and another term we'll cover is hydrophobic they fear water they stay away from water so all of these are nonpolar but these aren't the only ones right so don't just think oh I just need to memorize this or I'm done they understand what nonpolar means and why these are nonpolar