 So, let's calculate the energy of the n equals 2 state of the hydrogen atom in Joules per atom. Okay? So, let's see if we can do that. So in order to do this, we have to use Bohr's equation. So, remember, E n equals negative R hc over n squared, and it said that the energy level of our hydrogen atom is n. So what is the energy level? Negative. So, again, I like to put them all together to where I can cancel the units out. So, the Rhyberg rule in this case, right? So hopefully you guys can see we can cancel out meters there, meters there, seconds there, seconds there, and we're going to get Joules, and this is Joules per hydrogen atom. So, a small value, okay, you would expect a small value from one atom or we'll say 5.45. We'll say it's set to three significant figures, because with these ones, the only significant figure is real. N is an integer, so that would be to n-hemp and number of signals per atom. And then there's another part of this equation that says, what is the energy in Joules per mole? Okay? So, let's just continue along with this. So I'm going to erase all of this down here. Is everybody okay with that? Joules per atom, right? So energy to 2 times 10. That'll give us a kilojoules per mole. What's about this one? Think, though.