Lewis Dot Structures: Neutral Compounds

Jules Bruno
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so realize when it comes to drawing lewis dot structures that there are many possibilities that exist. But these are the rules that we're going to follow in order to draw the best structure. Now, recall elements form bonds in order to gain electrons and become like the noble gasses, the nearest noble gas. If we take a look here at this example, question, it says, draw the lewis dot structure for formaldehyde molecule, which is C H. 20 All right, So in order to draw this, let's look over the steps. So Step one says we need to determine the total number of valence electrons of the structure recall Valence electrons equal group number off the element. So here we have carbon, which has four valence electrons, plus hide your two hydrogen. Each one has one, so that's a total of two Valence electrons, Oxygen's and groups six A. So it has six Valence electrons. Adding all that up together gives us 12 total valence electrons. Now, step two, we're gonna place the least electro negative element in the center and connect all elements with single bonds. All right now, there are exceptions to this exceptions. Hydrogen can never go in the center. Recall. Hydrogen only needs one mawr valence, electron toe. Adopt the same type of numbers of valence electrons, helium so it doesn't It can't be in the center. It be overflowing with electrons. Also halogen. It's so remember the elements and groups. Seven a. So flooring, chlorine, bromine and iodine They Onley make single bonds as a surrounding element. All right, so what we're gonna do here is we're gonna put into practice what we just said, so we can't put hydrogen in the center, so our next best option is carbon. So carbon goes in the center, and then we're gonna place hydrogen ins and oxygen just to keep it like symmetrical. I put the hydrogen on the sides and the oxygen at the top. We said we're going to connect all of these elements with single bonds. So we're going to connect single, single and single. Now, add electrons, toe all surrounding elements until they have eight electrons following the doctoral. So we want them to have eight octet electrons around them. Exceptions. Hydrogen Onley want to octet electrons around them because again, when they get to to walk to the electrons, they behave just like helium. Their nearest noble gas. All right, so oxygen. We needed to have eight octet electrons by following the octet role. So right now we have these two electrons. Seoul 567 and eight actual. Let me bring that down. So we get a better look at it. So carbon goes here, and then we're connecting the hydrogen and we're connecting the oxygen. Okay? And then we have again these two electrons that are within this bond, oxygen needs eight or 34567 and eight. Right now, place any remaining electrons on the central element. So realize how many electrons have we used so far? We have 56789 10, 11, 12. So we have 12 electrons already used. So we don't have any additional electrons left to put around the carbon atom. But this is what's important for Step five. If any elements don't have eight octet, electrons add double or triple bonds between them. If we look, carbon has 246 electrons around it. It needs two more to get to the octet role. So what are we gonna do? We're gonna use one of these pair of electrons and bring it down. And when we do that So I'm gonna take these pair of electrons and I'm gonna bring them down and make a double bond with the carbon. So now we have a double bomb with that carbon. And now carbon has a total of eight electrons around itself. So it's following the octet rule, and the option of above is also following the octet role. Now Step six. The formal charge could be used to determine if the lewis dot structure is drawn correctly. The Onley allowable formal charges for an l A for an element ar minus 10 or plus one four stability draw the structure that gives least former least formal charges or lowest formal charges, and realize you're gonna put the negative formal charge on the Mawr electro negative element because that tends to be the most stable in this case. We don't have to do that because we see that the oxygen is following the octet rule by having a total octet electrons around it, same with carbon hydrogen Onley make single bonds. So we see that they're both making single bonds so we know they're satisfied as well. So that means for the formaldehyde molecule, we have hydrogen single bonded, and then the oxygen and carbon would be double bonded to one another. And then the oxygen would have these four non bonding electrons around itself. So this would be the best structure for formaldehyde.