In this video, I want to introduce the concept of energy states. So molecules are always in motion. And we're always talking about a collection of molecules. So some molecules will move faster than others. Others will move slower than others. And if we zoom in here, we also see internal motion that the molecules have different internal motions. Some rotate faster, vibrate faster, change confirmation faster than others. So that's the different energy states, right? They correspond to different kinds of motion. And the probability of having a particular motion depends on the energy through this formula, which is the Boltzmann distribution. But here I want to focus on what these energy states are exactly. We're going to do that by looking at a simpler molecule, HCl. So even for HCl and a simpler molecule, you can see that the motion is quite complex. And we can deal with that by breaking it down into separate contributions. So for example, vibration. And even for vibration, there's several different energy states with more and more vibrational energy. So the same is true for rotation. In the ground state, there's actually no rotation at all. And you can go to the next higher energy state than and see rotation. And as you'll see, as you go to higher and higher rotational energy states, the molecule will rotate faster and faster. Finally, we have translation. So for example, you can move slowly in the x direction or faster in the x direction. And of course, you can also move faster or you can move in the y direction. So each separate translational motion has, again, different energy states depending on how fast you move. So we can combine these things. We can assume that's an approximation, but we can assume they're additive. So molecule has vibrational energy, rotational energy, and translational energy. So we assume that these are additive and this allows us to describe complex motion.