Determine whether each molecule in Exercise 35 is polar or nonpolar. a. PF₃ b. SBr₂ c. CHCl₃ d. CS₂

Video transcript

hey everyone. So today we're going to be taking a look And identifying the polarity of four different molecules. Let's start with the first one H two S. C. Or hydrogen cell inside, so to identify the polarity of the molecule, it's easiest to draw out the lewiS structure of the molecule and then identify any diaper moments that may be there. So to draw the lewis structure. The very first thing we need to do is identify how many valence electrons there are within the structure for hydrogen Sinai, this is fairly easy. Each hydrogen will only have one valence electron. There are two of those. And selenium Which is a group six element similar to oxygen Will have six valence electrons. Therefore hydrogen sulfide or H two S. C. Will have eight total valence electrons With that in hand. We can go ahead and start drawing out our structure. Selenium will be our central atom and it'll be really bonded two two hydrogen atoms each way single Barnes note that each single bond as two electrons. So that means our structure right now has to four. It has four valence electrons present now to add the rest the remaining for veiled electrons. We can't add them on the hydrogen because hydrogen already has its full octet which in this case is only two electrons. So instead we added to the selenium central atom and we're done with our lewis structure. We have eight electrons due to the repulsion forces from the lone pairs, the atom gets a bent shape as we can see here and because of this bent shape and because of electro negativity trends since selenium is further to the right on the periodic table, then hydrogen, selenium will be far more electro negative. And there will be a diaper moment pointing up towards the selenium from both hydrogen, which means there will be a net die paul going straight up because the left and right components of these diet polls will cancel out, Which will leave us with one big die pole heading straight up. So hydrogen Soleil need H two S E is a polar molecule and will denote that with red. It's a polar molecule. Let's take a look at the next one, BI three or boron tri iodide is pretty fun to work with boron Generally has three valence electrons and iodine has seven valence electrons. And since we have three of them, That'll leave us with 21. So in total we'll have 24 valence electrons for boron dry iodide. Let's draw this out So poor on will be our central atom and it'll be single bonded to three ideations. So that will leave us with six electrons already And we still need 18 more and we can add these as lone pairs to the iodine because their octet, it's need to be filled. Now you may be wondering why aren't we adding any to the boron. And that's because if we are to actually calculate the formal charge of the boron atom in this molecule, we'd see that it actually has a formal charge of zero. So even though it doesn't have a full eight electrons boron is actually in its most stable state at the moment. So we don't have to worry about that. And now we have eight 24 Valence electrons in a molecule and we're good to go now. Similar to how I mentioned with selenium and hydrogen. Earlier periodic trends dictate that electro negativity increases as you go from the bottom left to the top right of the periodic table. iodine is further right on the periodic table than boron. So each of the B. I bonds are actually polar bonds. However, due to the symmetry that we see in our molecule, all the disciples actually cancel out which means even though each bond is polar boron dry died is a non polar molecule. It is non polar. Let's move on. Ch three or Floral. Methane is pretty simple to find. The valence electrons for Carbon is a group four element. So it has four valence electrons. Each hydrogen will have one and there are three of them. And flooring is a halogen, it's in group seven. So it has seven valence electrons. That means seven plus four or sorry, seven plus three is 10 plus four is 14 valence electrons. Now let's try that out 33. So by now we should pretty much get the drill carbon will be our essential atom and it will be co violently bonded 2, 3 hydrogen atoms. And that gives us six electrons in the valence structure. Already. The lewis structure sorry and it will be bounded to florida. So that brings our violence like current total to eight which means we still need six more. Which can all go sorry, we can all go on the flooring. So now we have 14 total valence electrons and mhm. The eight C bonds, hydrogen carbon bonds are non polar covalin bonds because the election negativity difference between them is very very low. However, since flooring is the most election negative element on the periodic table, it will form a diaper moment here. This is far more electro negative than carbon. And this will mean that we have a single typo pointing up. So it is a polar molecule. Let's take a quick look at the last 1. Nitrogen is a group five elements. So it has five valence electrons, florian has seven and chlorine also has seven. And we have to those so it's 14 plus 7. 21 plus 5. 26 total valence electrons. Now let's try that out. We have n we have yes that we have two C. L. S. So we have six electrons here. We can add in and fill in each of the arctic But that'll only get us to 24 electron. So now we can add the remaining two to the central item. And we're done the valence or with the lewis structure from here. All three bonds are pollock oh. Vaillant bonds since chlorine and florin are farther to the right on the periodic table than nitrogen and are far more electro negative. However, the election negativity is of chlorine and flooring differ. So the left and right components of the chlorine depot moments will cancel out leaving us with a diaper moment headed down, it'll be headed down, but there'll be a larger diaper moment headed up. So even though there's an up and down dipole moment, because they're unequal, that will mean that our molecule is polar. It is polar. So there you have it hydrogen cell a night is polar boron. Tried at his non polar flora. Methane is polar, and NFC L two is also polar.