 So, I just taught you the formula for electron capacity of principal energy level can hold, okay? So what we're going to try is to figure out how many electrons each of these principal energy levels can hold by just identifying what their principal energy level number is, okay? So, again, what is the electron capacity for a principal energy level? How do we figure it out? Two and to the what? To square, right? So that's the, we'll say, electron capacity. So everybody okay with that? Wonderful. Even the people that didn't answer? Okay, wonderful. So, and remember that's the principal energy level. It'll always be written as n, okay? So, this n equals one would be two and we'll just plug and chug. One squared is what? One, right? Times two. So, the first energy level can hold two electrons. If we look at the periodic table, isn't that the case? Right? The first energy level can only hold two electrons. What about the second energy level? So that'll be one. We'll say electron capacity for two is going to be, again, two n, but n this time is two, right? Squared. So what's two squared guys? Four. Four times two? Eight. Eight. Is that how many you would have expected from looking at the periodic table? Yes. Yeah, it is, right? Okay. What about the electron capacity for three? So it's going to be two, three squared, right? So what is that answer going to be there? Eighteen. Eighteen. Is that what you would expect from looking up there? Very good. And then the last one, electron capacity for four, two to the four squared. So it's four squared. Sixteen. Sixteen times two. Thirty-two. So two electrons for the first one, eight electrons for the second one, 18 for the third one. Any questions on this?