(b) Draw the Lewis structures of two example THMs.

Video transcript

Welcome back everyone in this example, we have try hallow methane as a class of molecules with one central carbon atom bound to one hydrogen and three halogen atoms. We need to choose the pair that are both trihalomethanes below. So we want to first recall what our halogen czar on our periodic table And recall that that is in group seven a. Specifically covering flooring. We have chlorine, bromine and iodine. So looking at our choice A. We can see that we have a central carbon atom. So that's a check and it should be bounded to one hydrogen atom at least and then three halogen atoms. So in these places we see a second hydrogen atom and then a third hydrogen atom here, and only one halogen being our chlorine here. So we can already rule out choice A. Because this is not going to be a try hallow methane. We can also consider the molecule next to it. Not a tree hollow methane as well because it also has just three bonds to hydrogen and just only one halogen. It's missing to other religions. So moving onto choice B. We see our central atom carbon and we see that it's bonded to one hydrogen in each. And we can count a total of in the first structure to bonds to bromine, which are halogen and then one bond to chlorine, which is the third halogen. In the second structure, we can count three bonds to chlorine as the only halogen present because we do have that combination of a carbon bonded to a hydrogen and three halogen. In both of these molecules, We're going to confirm that these are both try hallow meth eins, meaning that choice B looks like a great answer choice. So moving onto choice C. We're going to see that we have our central atom carbon. We have a bond to hydrogen in each, but we can see that this first structure has two bonds to hydrogen and we only need one bond to hydrogen. So even though the second structure here is a try hello methane, we can't consider this first structure. A try Hello methane. This is not a try. Hello methane because again it has these two bonds to hydrogen. It only should have one bond to hydrogen and three bonds to halogen. So we can rule out choice. See moving on to choice D. We can instantly see that we have two bonds to hydrogen again in these two structures, meaning that these are also not trihalomethanes. And we would rule out choice D. So this means that the only correct choice to complete this example as a correct choice for a pair of trihalomethanes is choice B. Because we see that choice B had two structures with carbon in the center bonded to one hydrogen atom and a set of three of any of our religions. So B is our final answer. I hope everything I reviewed was clear. If you have any questions, leave them down below and I'll see everyone in the next practice video