 So the next one says polonium metal crystallizes in a simple cubic unit cell with the edge length of 334 picometers. What is the density of polonium and grams per cubic centimeter? Okay, so A few things about this well first thing. Let's write the edge of this are the the distance of the side down so 334 Is that's given to us And it wants the density and grams per cubic centimeter. So that's something to remember if you can Remember the formula that kind of gives you a clue, but anyways, there's a formula for this, right? D density Equals z which is the number of lattice points per unit cell times the molar mass of the metal Divided by the side cube times Avogadro's no so Polonium the polonium atom it's died is 334 picometers So we've got that molar mass is 209 right so 209 grams per mole I'll do that Of course Avogadro's number 6.0 22 turns 10 to the 23rd molecules Or in this case atoms Atoms per mole, let's just say that And Z well when we say that was the number of lattice points per unit cell so the simple cubic, right? it's eight of them because they got one Two three four five six seven eight One eight because only one eighth of each one of those atoms is in the unit cell So that equals one so now it's just a matter of plug-and-chug The only thing you got to remember is This is in picometers, and it wants it in centimeters, okay? I'm a good conversion for you guys to Remember just so you don't have to do this every time because you convert from picometers to centimeters But it is one times ten to the ten Heek of meters is one centimeter. So it's three point three four Plug-and-chug so that equals lattice points is one 209 Grants for one mole Yeah, but that's meters Thanks for noticing At least you're paying attention Okay, so where were we so we're looking for the side now, right? So three point three four times ten To the negative eight at a cube that we got to this number six point oh two two times ten to the twenty-third Cool with that So notice cancel there all mole and what do we get? centimeters cube down here and grams up there So let's go about Chugging now so one times two oh nine is Two oh nine divided by that And I get an answer that we're going to do three six things right since it was three thirty four was given to us is nine point three one grams So that's the density of Everybody okay with any questions on this type of problem again got to memorize the formula