So these patterns are important, and for oxygen, twoīonds, and two lone pairs of electrons give us aįormal charge of zero. ![]() Of electrons around it, so let me highlight those, two, four, six, and eight. Them in here for convenience, but I could go ahead and add them, so it's easier to see that that oxygen has a formal charge of zero. On the right, we have another example, where oxygen has a formal charge of zero, and this oxygen has two bonds to it so here's one of the bonds,Īnd here's the other bond, and this oxygen would also have to have two lone pairs of electrons on it, and again, I didn't draw them in here. ![]() So I'll highlight them, two, four, six, and eight. So we have a total of eight electrons around our oxygen, so oxygen's following the octet rule here, There should be two pairs of electrons on that oxygen, so youĬan put them in there or you could leave them off. The lone pairs of electrons have been left off this dot structure, but we know, since theįormal charge is zero, we already have our two bonds here. One on the left first, so the formal charge is equal to zero on this oxygen and we can see we have two bonds here to oxygen, here's one of the bonds to oxygen,Īnd here's the other bond to oxygen. Let's look at some other examples, where the formal charge on oxygen is equal to zero, and we'll look at the Pairs are just left off for convenience reasons, right, so you could draw this with your oxygen, and your hydrogen like that, or you could even go like this, and all those are just different ways of representing the same molecule. When oxygen has two bonds, and two lone pairs of electrons, one oxygen has two bonds and two lone pairs of electrons, the formal charge is equal to zero. Write down this pattern that we've just seen. We have one, two, three, four, five, six, so there are six valence electrons around the oxygen in our drawing, so six minus six is equal to zero, so the formal charge on oxygen is equal to zero. So now we have a total of six electrons around our oxygens, so ![]() All right, same thingįor this other bond here, oxygen gets one of those electrons, and the other electron goes to hydrogen. So from these two electrons, oxygen gets one of those electrons. Now remember when you have a bond with two electrons, we give one electron to one atom, and the other electron to the other atom. Made up of two electrons, and our goal is to find the formal charge on oxygen, so the formal charge on oxygen is equal to the number of valence electrons in the free atom, so the number of valence electrons that oxygen is supposed to have, we know that's six, right, oxygen is supposed to have six valence electrons, minus the number of electrons that oxygen actually has in our drawing. Remember that each bond is made up of two electrons, so this bond right here is made up of two electrons. We've already seen that formal charge is equal to the number of valence electrons in the free atom, minus the number of valence electrons in the bonded atom, and another way of saying that is the formal charge is equal to the number of valence electrons the atom is supposed to have, minus the number of valence electrons the atom actually has in the drawing, so let'sĪssign a formal charge to oxygen in this molecule. Remember each bond is 2 electrons, and each lone pair is 2 electrons.įormal charge = # of valence electrons - # of lone pair electrons - # of bonding electrons/2Ģ bonds and 2 lone pairs = 6 - 4 - 4/2 = 0 formal chargeġ bond and 3 lone pairs = 6 - 6 - 2/2 = -1 formal chargeģ bonds and 1 lone pair = 6 - 2 - 6/2 = +1 formal charge Note I'm using a different method to calculate formal charge from Jay, I feel this one shows you where the numbers come from better. If you see oxygen with 3 bonds you can assume there is 1 lone pairĪnd from that information you can instantly know the formal charge on any oxygen too. If you see oxygen with 1 bond you can assume there are 3 lone pairs ![]() If you see oxygen with 2 bonds you can assume there are also 2 lone pairs One thing to note is that oxygen is always going to follow the octet rule, that is it will always (at this level at least) have 8 electrons around it even if they are not drawn in. What time in the video is this? There are many molecules in this video so I'm not sure exactly which you're meaning.
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