General Chemistry Problem Help1

this is number 107 it's a cumulative problem and it's looking at some more difficult uh Lewis uh structures and so I'll go through all of these and the first one part A is looking at cl207 and we have a hint here there is no chlorine chlorine bond in the structure so somehow we have to get this molecule such that well chlorine is not bound to itself but also notice that this molecule is neutral so we have to figure out a way to have a neutral charge for this structure and so to break it down we have to you know basically look at well each oxygen here and we have seven of them right each oxygen wants two Bonds in order to be neutral and so if there's seven oxygens that means that you have to make 14 bonds at some point with these total amount of oxygen and then we look at chlorine and chlorine has seven veence electrons but only one is unpaired and there are two of them so somehow we have to find a way to to have these two chlorine atoms bind to seven oxygens and so that means that if well each oxygen requires two bonds that means each chlorine really needs to make seven bonds to account for the 14 total that's in the structure and so in order to do that in order for chlorine to have seven bonds it needs to fully expand its octet so that each electron is unpaired every lone pair is split and so while in this form chlorine would only want to make one bond in this form chlorine can actually make seven bonds and so now we can start to put the structure together knowing that fact if chlorine can make seven bonds well then it can make three three double bonds with three oxygens to end up with something like this so now it's used six of the seven so it actually still has one electron left over and this is why we have the hint no chlorine chlorine bond because now what we're going to do is put an oxygen in the middle once we have oxygen in the middle we're going to do the same thing that we did for the first chlorine we're going to do it for the second chlorine because it can do the same thing it can bind seven times and it needs to in order to make sure the molecule is neutral and so we end up with this structure for cl207 and I know that kind of looks really funky because we see chlorine with so many bonds to it it looks like it should have some type of formal charge so let's let's see if it actually does or not we know oxygen is going to be neutral because it simply used its two unpaired veence electrons and that's kind of a a quick trick to get at a formal charge of zero but let's look at chlorine chlorine has that seven uh veence electrons it has in this case no electrons in Lone pairs in the structure and then it has plus 12 1 2 or 2 4 6 8 10 12 14 electrons in bonding and so again we get a zero formal charge we can use the same trick for oxygen as with chlorine remember the trick that I said was that since oxygen used its two unpaired veence electrons to bond that's why it's neutral and we can do a calculation to prove that chlorine is the same way if chlorine makes one Bond as in the structure I first showed in the Lewis Dot sense for chlorine then yes it is neutral but if chlorine expands as octet and in this case has seven unpaired valence electrons if it uses all seven of those electrons to make bonds then also it would be neutral and that is what we see here with cl2 7 the next one is looking at phosphorus acid which is H3 po3 and we're also given a Hint by saying we have two Oh's um in the actual uh structure and so we're going to put um phosphorus in the middle and so phosphorus normally likes to have three uh bonds um but remember it can expand its octet as well we also know that we have two o is that we have already formed given our hint above so we have two of those and then we still have one oxygen left over so this molecule really or this part of the molecule really only wants one bond in order to be happy in order for oxygen to have its octet same for the other o they're identical and then the last oxygen wants to make two Bonds in order to be neutral so we have one 2 3 4 we've accounted for every element for one which is hydrogen we still have one more hydrogen to take care of and that also wants one Bond we know there are no more O's so that means that that hydrogen is going to be bound to the phosphorus but we could also figure that out by looking at the number of bonds we need to make to the phosphorus 1 2 3 4 5 we need to have five bonds to the phosphorus and in this state phosphorus only can make three three bonds but it can expand its octet in order to make five bonds and that's what phosphorus is going to do it's going to make a single bond with each one of the O's it's going to make a single bond with the last hydrogen and so now we've accounted for three of phosphorus 5 electrons and so the last two electrons it's going to use to make a double bond with the remaining oxygen and so we get a structure for phosphorus acid to look like this which is fairly similar to phosphoric acid except we just don't have that other oxygen we have a hydrogen in this case bound to the phosphorus so that is H3 P4 or I'm sorry H3 po3 the last structure is looking at arsenic acid H3 aso4 arsenic is just under phosphorus on the uh periodic table so you could think about this as being the same almost as H3 P4 since phosphorus and arsenic are both in group 5A they have the same types of properties and so if we look at this uh molecule we look at ARS uh first it has those five veence um electrons two of which are in a lone pair and so if we start to put this uh together by looking at the elements that we have we need to somehow bind all of these guys and so one trick especially for the acids and we can recognize acids Again by having those hydrogens written first in the structure is we can actually make three oxygen hydrogen bonds and so if we make three of those oxygen hydrogen bonds that means we still have one oxygen yet to deal with and then we also have our our arsenic with its five so that means for the O's we need to make three Bonds in order for the oxygens to be neutral for the other oxygen we actually need to make two bonds and then for the Arsenic somehow it has to incorporate both of those motifs the O and and the monoatomic oxygen and so while in this state arsenic can only bind in in three and as far as the number of bonds it can make because it only has three unpaired bance electrons we want to expand its octet just like we did with phosphorus earlier so that it has five unpaired electrons and now with five unpaired electrons it can facilitate bonding with those three O's and that one monoatomic oxygen by having three single bonds to the O's and then that takes care of the three unpaired below and then we still have two above and that's going to make the double bond with the last and final oxygen and so we end up with a structure that looks like this which is exactly the same as with phosphoric acid and that would make sense because Arsenic and phosphorus are part of the same group group 5A and so they share the same type of chemistry that is number 107