Which is the best electron-dot structure for the thiosulfate ion (S2O3 2-) based on the rules of formal charge? (LO 7.16) (a) (b) (c) (d)

Video transcript

everyone's in this video. We see that we have three different electron dot structures and we're trying to see which one is the best structure for bromine ion which has a formula of B R 03 minus. Of course the overall charge of these formal charges are equal to just negative one. So taking a look at structure one take a look at all these structures. Actually we see that we have already the formal charges for oxygen. It's a little bit hard to see. So let's go ahead and emphasize those first Infrastructure one. We have a negative one charge on this bottom oxygen atom for structure two on the right and left auction, we have a formal charge of negative one on both. And last infrastructure three all three oxygen atoms will have a formal charge of -1. All right. So we can see that all the formal charges for auction already drawn in. So we simply need to focus on our browning atoms. So the formula for a formal charges equal to group number subtracting from the sum of our bonds plus our non bonding electrons. So this is the proper formula for a formal charge. Another way I like to put it when I am teaching my students is group number subtracting from the son of the some of the bonds, the bonds is just lines and our non bonding electrons are dots and that's our lone pairs. So this is the formula I usually tell students to kind of keep in mind when we're doing exams or quizzes because this is a lot easier to refer to. All right. So using either method then we can go ahead and calculate the formal charges of our bromine atoms. So starting off with structure one here, which I'll do in this blue color for one. So we have our group number of grooming equaling 27. So formal charge, I'll simplify that as fc. So again, group number is seven. We need the lines, we see here that we have two double bonds. So that's four lines total. And then we need to count the dots and that's just to from our one lone pair on top. So we have two lone pairs. But we also have our one single bond connected to this oxygen right here. So we're going to add that in as well. So you see we simplify within the parentheses, we have that equaling 27. So of course seven minus seven gives us a formal charge on that bro. Mean to be equal to zero. And of course because we have a neutral bromine, then this means that the overall charge of structure one is equal to negative one which is matching to this eye on here. So now moving on to structure to I'll do this in purple. So again, the former charge simplified to F C. We have the group number being seven. So of course it's just the same for the lines here for this bombing. We have two single bonds and then we have one double bond which contains two lines. And lastly we have one long pair. So we have two dots Again some flying wets and apprentices first. That's equal to six. So 7 -6 is equal to positive one. So from a charge for this browning is equal to positive one. I'm moving on to our structure number three. Our last structure here Again, the group number for browning is seven were kind the lines here, we have three single bonds. So that's just three. And then for our dots we have two lone pairs. So three times two is equal to six Or three times or two times two. I apologize. We have two long pairs. So two times two is equal to four. So we have three lines and we have four dots total on this central brewing atom. So again simplifying what's in their parentheses, three plus four is equal to 7 to 7 minus seven gives us a formal charge of zero on this browning. So this means that our overall charge for a structure number three then is equal to negative three. We don't have a negative one charge here. So structure three is automatically eliminated from our answer choices. And we can see from a charter to that we have a positive one and negative two charges here. So one of these will cancel leaving us with the overall charge of negative one on a molecule. So it's either between structure one and structure to or formal charge roles for electron dot structures that we want to go ahead and minimalize how many formal charges we have in the molecule, we see a structure one that we only have one formal charge on the oxygen structure to. We have a total of three different charges. So of course one is less than three. So we want structure one to be the best um, choice for our eye on here. So answer A is going to be our final answer for this problem.