Carbon and oxygen combine to form the molecular compound
CO2, wh...

Question

Carbon and oxygen combine to form the molecular compound 
CO2, while silicon and oxygen combine to form a 
covalent network solid with the formula unit SiO2. Explain 
the difference in bonding between the two group 4A elements 
and oxygen.

Accepted Answer

Hello. In this problem we are told the carbon dioxide is a molecular compound while silicon dioxide is a Covalin network solid. Why do carbon and silicon bond differently? Even though they are both from group four A elements. This begin by looking at the filling of the orbital diagram and we're just going to consider the valence electrons. So if we look at carbon, carbon is in period two. So it will be filling the two S. And the two P orbital's. So carbon has two electrons in the two S. And two electrons in the two P orbital's. So we can take one of these two S electrons and promote it to a higher energy state. In doing so, we then have an S orbital with one electron and each of the P orbital's has one electron. We have four lone electrons that can form four bonds which we know is typical of carbon. So we can take one of the two s and one of the two p. And we form two sp hybridized orbital's and then we have two P atomic orbital's left over. So drawing carbon, then we have carbon. It has to S. P. Hybridized orbital's and it has to P atomic orbital's. Now let's consider oxygen. Oxygen is also in period two. So we are filling again the two S and the two P orbital's with oxygen. So oxygen has two electrons in the two s. and four electrons in the two p. We will take one we will take the two S And two of the two p. And we will form three S. P. Two hybridized orbital's And we will have one p atomic orbital left over. So drawing oxygen Then oxygen has three S. P. Two Hybridized orbital's and it has one p atomic orbital. And let's draw two of these so that we can continue our discussion then with silicon. Alright. So moving on to silicon. Silicon then is in period three in period three recall. We're filling now the three S and the three P orbital's. So silicon has two electrons in the three S and two electrons in the three P. And we can take one of the three S electrons of silicon and promote it to one of the empty three P orbital's. Doing so we now have three S Orbital with one electron and we have three p orbital's each with one electron. So we have four free electrons again, as we did with carbon. And so silicon can also form four bonds. So we are going to take one of these three S and one of these three P. And we're going to form then to sp hybridized orbital's and we will have two P Atomic Orbital's left over the drawing Silicon is going to look similar to that of carbon. So silicon has to sp hybridized orbital's and it has two p atomic orbital's recall that as we go down the periodic table, that the size of the orbital's increases. So the silicon s P orbital's which are three sp orbital's are larger than those from carbon which are two sp hybridized orbital's. So when we form bonds between carbon and oxygen, this bond where this S. P orbital is short for carbon as compared to silicon, this is larger. And so when we go to form a bond due to the overlap of these hybridized orbital's, then the carbon oxygen bond will also be short as compared to the bond between silicon and oxygen. This will be larger due to the larger size of the three sp hybridized orbital of silicon. So the shorter bond then between the carbon and oxygen hybridized orbital's allows for the overlap of the p orbital's side by side overlap, which then results in the formation of a pi bond. This head to head overlap that we saw with the hybridized orbital's produces a sigma bond. And so we can produce a sigma bond between the oxygen and silicon. But due to the larger size of that bond, it is not possible to form a pi bond due to overlap of the p orbital's between silicon and oxygen. So there's no pi bond. Okay, because the larger size prevents that. So when we think about carbon, so as we showed carbon has four loan electrons, so it can form four bonds and so it can form a sigma bond Due to overlap of the SP orbital's of carbon and the SP two more bottle of oxygen and we can form a pi bond, youtube p atomic orbital overlap With Silicon. Silicon also can form four bonds. It has four loan electrons, but it can only do through so through the formation of single bonds. So we are only able to form a sigma bond where we have overlap of the S. P orbital of carbon and S. P. Orbital. I'm sorry, of oxygen sp two and sp orbital of silicon. Um the pi bond, it's not possible. So that means then the silicon will form these extended Van Covalin network solids, whereas carbon and oxygen form molecular compound. So if we go back to our answers that were provided A says that silicon forms four bonds with four oxygen atoms because it is larger than carbon and oxygen. So the silicon three P orbital and the oxygen two P overlap will not be as favorable as the carbon two P orbital and oxygen two P orbital overlap. So that is the correct answer. We look at the other answers that are provided. The next one says carbon forms four bonds with four oxygen's. So we know that's not true. Carbon forms four bonds with two oxygen's. So that eliminates B. And next silicon forms two bonds with two oxygen's and again, that's not true either. Silicon will form a bond with four different oxygen's and the last one says carbon forms two double bonds with two oxygen's because carbon is smaller than silicon. So the carbon two P orbital and the oxygen two P overlap will not be as favorable. so this part is not true, and so that eliminates D is a possible answer. So the correct answer to this problem is given by a thanks for watching. Hope This helps.

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