 And I wouldn't you know it. I forgot to delete the old videos off this cheap old fire tablet right out of memory So part two of the study guide review picks up right where we left off now at question number 25 Which of the following is not a property of covalent substances while covalent substances are soft low melting and boiling point Don't conduct electricity And they tend to be liquids and gases at room temperature So which of the following is a property of them soft. Oh, not a property. Oops my fault Am I gonna start over? Heck no Not would be high Soft is one of the properties don't conduct and low boiling points. Those are all properties B is the answer for that Hey, I'm moving on to 26 Considering that Lewis structure We're gonna describe this as a substance that contains all this is polarity So let's take a look at polarity phosphorus is 21 and the 21 2.1 and Chlorine is a 3.0 for an electronegativity difference of 0.9 That makes polar bonds so Automatically when many of those two we know it's got polar bonds now. We just got to figure out if it's a polar molecule lower number is positive Higher number is negative If you can draw a straight line Put all the negatives on one side the positives on the other it is a polar molecule. So that brings it down to a 27 When bonding with a halogen like fluorine carbon is capable of forming what well to answer this question We have to look at Lewis structures Carbon's got four valence electrons, which means four single dots carbon can make four bonds Halogens like fluorine Have seven valence electrons It can only make one so again Carbon can make up the four bonds, but fluorine can only make one that is going to limit us to nothing but single bonds We could do the whole Lewis structure and everything if we wanted to to confirm that Then you got it. Everything's a single bomb We're gonna help that in time here Let's give booking Next question same kind of question this time it's nitrogen and carbon so carbon again Four dots can make four bonds nitrogen has three dots That means that We can make a single bond with carbon We can make a double bond with a carbon or we could go all the way up to the triple They can make a mix of single double and triple bonds depending on what else it has to bond with You're limiting factors never gonna be carbon carbon can make four bonds no matter what you're limiting factors gonna be what it bonds with and If it's binary then it's gonna not work because carbon also have an extra electron there We need something like hydrogen over there to pick it up But it can make up to three bonds so it can do single doubles or triples when nitrogen is concerned It just depends on what else is there to bond with it wouldn't be binary, but it could go all the way to triple Which of the following formulas an empirical and molecular empirical means reduced Molecular means covalent So it has to be a covalent substance that means no metals It has to be a compound so that can't have an element in there comes down to those two Two non-metals so that's covalent. That's a molecular formula two non-metals. That's covalent So that's a molecular formula, but this one is four and eight that is not reduced That one is two to one that is both an empirical and a molecular formula. It's reduced and it is of a covalent bond molecule Gas is going to be C particles far apart Strongest number like of the forces are in a solid a In strongest middle weakest none at all actually strongest weaker none at all that's what to think about it To go from B to C to go from liquid to a gas we have to remove intermolecular forces A When you melt something you weaken them when you boil something you remove them A to B that's melting so again, we would weaken them They're strongest in a solid weaker in a liquid nonexistent in a gas Liquid a room temperature. This is about intermolecular force We want to recognize that there's three types and covalent substances. There's hydrogen bonding Which would happen here with nitrogens and hydrogens So that would be hydrogen bonding There are dispersion forces which would happen in elements and non-polar substances Carbide oxides non-polar so that would be dispersion forces remember Even though the polar bonds, it's a linear structure. So there's no separation of charge and PCL Three would just be plain old polar because you do have separation of charge We'd look at that one already on the test So that would be dipole dipole Hydrogen bonding tends to have the highest melting and boiling points. So it's the one that's most likely to be a liquid at room temperature We consider molecular forces again. We're looking at these three things once more F2 we know that's going to be dispersion forces H2o hydrogen oxygen bonds and we know it's polar that it's going to be hydrogen bonding Si2 is bent Sulphur acts just like oxygen iodine acts just like hydrogen So it's a bent molecule just like water is sulfur is a 2.5 iodine is a 2.5. So these are non-polar bonds So this has got dispersion forces And then CH4 I should probably label this one this question differently It's a tetrahedron because it's five atom molecule carbon-hydrogen bonds are polar bonds, but no actually they're not They're only point fours. So these aren't polar bonds at all. So those are dispersion forces again. So it could be any of those things really I'm gonna say F2 because it's an element and the electronegative differences is zero in that As it is here, but yeah, I should probably sit strongest here. And if I said strongest that would have been hydrogen bonding oops last two questions mole ratio problems We're going from oxygen to iron three oxides oxygen to that three moles of oxygen equals two moles of Iron three oxides Start with a given 3.5 moles and that's oxygen Set this up so oxygen cancels And do your math 3.5 times 2 divided by 3 Grab my calculator here. So I always like to make sure I give you the right answer 3.5 times 2 is 7 divided by 3 It's 2.3 So be the answer Same kind of set up for the second one, but this time we've got iron and we want to know oxygen. So iron and oxygen four moles of iron equals three moles of oxygen We're starting with 1.5 moles of iron Set up so the iron cancels The three moles of oxygen on top But how many times have we done this? 1.5 times 3 that's 4.5 divided by 4 is 1.125 That's an amazing answer All right, that's it loads of fun. You'll all ace it because you're all geniuses. I Got faith in you. You have faith in you