Draw the electron-dot structure for CO, CO₂, and CO₃^2–, and predict which substance will have the strongest carbon–oxygen bond.

Video transcript

All right. Hi, everyone. So for this question, let's consider the substances, CS CS two and C S3, 2 negative provide the lowest structure for each substance and identify which will have the strongest carbon sulfur bond. So first, let's go ahead and proceed with the first fluid structure of CS or carbon monosulfide. Recall that the first step is to find the number of valence electrons that each atom in your molecular formula will contribute. Right. So if my molecular formula is C si have two atoms, in this case, one is carbon and the other is sulfur. Now recalled carbon belongs to group four a of the periodic table, which means that it has four valence electrons and sulfur belongs to group six A which means that it's going to contribute six valent electrons. So because because these are the only two atoms in my molecular formula, when I add together six and four, I get that there are a total of 10 valence electrons to distribute in my Lewis structure. So in this case, I'm going to connect together my carbon and my sulfur atoms with a triple bond in between them so that I can use as many valence electrons as possible. Right? So after I make the triple bond between carbon and sulfur at this point, I have used a total of six valence electrons because I have a triple bond each with two electrons. So that leaves me with four in total that I have remaining. So my four remaining electrons are going to be used as a loan pair on both carbon and sulfur. And this is to make sure that both carbon and sulfur obey the octet rule. So now that I've distributed all of my valence electrons recall, the next step is to add formal charges as necessary. Right now, the formal charge or FC for short can be calculated by taking the group number of a given element and subtracting that by the number of bonds added to the number of non bonding electrons. So if I scroll down here to open up some space for myself, a formal charge of carbon is going to be the group number four subtracted by three bonds added to two non bonding electrons. And this gives me a formal charge of negative one which I will add to my Lewis structure. So now we can do the same thing with sulfur. The formal charge of sulfur is equal to the group number six subtracted by three bonds as well as two non bonding electrons. This gives me a formal charge of positive one which I will go ahead and add to my little structure. So now here is the lowest structure of carbon monosulfide. And now we can proceed with the lowest structure of CS two, also known as carbon disulfide. So I'll take my molecular formula which is CS two and calculate my total number of valence electrons. Now I have the same atoms right. I still have carbon and I still have sulfur. However, the quantity of each has changed, which does still affect the number of valence electrons, carbon is still going to contribute four valence electrons and sulfur is still going to contribute six. However, I have two atoms of sulfur in this molecule, which means that six valence electrons must be multiplied by two to give me a total of 12 electrons from sulfur. So when I add together four electrons and 12 electrons, I get that there are a total of 16 valence electrons to distribute. So in this case, right, because carbon is less electron than sulfur, carbon is going to be the central atom in this case. So I will put my carbon in the center and I will place both sulfur atoms on either side of it. Now, in order to ensure that the central atom has its octet, right. I'm going to put or I'm going to form I should say two double bonds between carbon and each of my sulfur atoms. Because by doing so, carbon has the four bonds, it needs to fulfill its octet. So now after I've created two double bonds. At this point, I have used a total of eight electrons, which means that I have six electrons or excuse me, eight electrons left over to distribute. So my remaining eight electrons are going to be placed on both of my sulfur atoms as two lone pairs each. So now the next step is to find the formal charge of both carbon and so forth, right, the formal charge of carbon is going to be equal to the group. Number four, subtracted by the sum of its four bonds and zero non bonding electrons. This gives me a formal charge of zero for carbon. Whereas for sulfur, the formal charge is equal to the group. Number six subtracted by the sum of its two bonds and four non bonding electrons, which also gives me a formal charge of zero or both sulfur atoms. So with that in mind, we have the complete Lewis structure for carbon disulfide. So now the last Lewis structure to find if I scroll down one more time to open up some space that is going to be oops C S3, 2 negative or trio carbonate. So once again, we're going to find the vant electrons of both carbon and sulfur. In this case, theres only one carbon, which means that I'm going to have a total of four valence electrons from that carpet. Now sulfur contributes six vent electrons. But when multiplied by the three sulfur atoms present here, that gives us a total of 18 valence electrons. So now 18 added to four gives 22 valence electrons. However, in this case, we do happen to have a charge of negative two. So that means that an additional two valence electrons must be added here to give the actual total of 24 valence electrons. So now carbon is less electron than sulfur, which means that it is going to be the central act. Now, the idea here is to first ensure that the central atom fulfills its octet. Meaning that first we have to make sure that carbon has four bonds. So in this case, there's going to be one double bond between carbon and sulfur and two carbon sulfur single bonds. So with that being done, right, I have one carbon sulfur double bond as well as two carbon sulfur single bonds. That means that at this point, I have used a total of eight valid electrons to fulfill the octet of carbon which when I subtract that from my 24 vent electrons that I'm starting with, that means that I have 16 left over to distribute as loan pairs of electrons on my sulfur atoms. So in this case, right, the sulfur that is double bonded to carbon is only going to require two lone pairs to complete its octet. Whereas the remaining two sulfur atoms are going to each require three loan pairs because they only have one covalent bond to carbon. So now all that is left is to go ahead and find the formal charges if there are any. Now, what I want to point out here, first and foremost is that the sulfur atom that is double bonded to carbon is going to have the same formal charge as the sulfur atoms in the lowest structure of carbon disulfide. Right, because it also has two bonds as well as four non bonding electrons. However, here we can go ahead and calculate the formal charge of the sulfur atom with a single bound, which is going to be equal to the group number six, subtracted by the sum of it's one covalent bond and six non bonding electrons that gives a formal charge of negative one for each of them. And carbon carbon has four bonds and zero non bonding electrons, which gives that a formal charge of zero as well. So at this point, we have found the three lowest structures, four are compounds. So now the question is which of them is going to have the strongest bond between carbon and sulfur. And to do that, we have to consider the fact that shorter bonds indicate that they are stronger. And it just so happens that among the three lowest structures that we came up with, we have carbon sulfur, single bonds, double bonds, and also triple bonds. Right now, triple bonds, if you recall are actually the shortest and therefore are the strongest. Whereas single bonds are the longest and therefore the weakest. So among the three types of carbon sulfur bonds that are present among the three lowest structures, right, the strongest carbon sulfur bond is going to be the one present in carbon monosulfide because carbon monosulfide has a triple wand in between carbon and sulfur, which is the shortest in length and therefore the strongest and there you have it. So here is your final answer, right? We have the three lowest structures for all three of our compounds and the strongest carbon sulfur bond is going to be found in CS or carbon monosulfide. So if you stuck around to the end, thank you so very much for watching and I hope you found this helpful.