recall that a hetero nuclear diatonic molecule is composed of two different elements bonded together. And we're going to say here that the less electro negative element determines which molecular orbital will be used and recall that electro negativity increases as moved to the top right corner Of the periodic table. Remember flooring is the most electro negative element with the value of four point up. Now we're going to say here that when it comes to displaying these molecular orbital's or these molecular orbital diagrams, the more electro negative element within the hetero nuclear di atomic molecules possesses atomic orbital that are lower in energy. So here, if we take a look, we have molecular orbital diagrams for hydrogen to helium for lithium to nitrogen and from oxygen to neon, if you watch my videos on molecular orbital theory, you're kind of familiar with these displays. Now if you notice, you can see here that this two s atomic orbital is higher in energy than this one. This one's lower down. That must mean that let's say we're combining work comparing carbon to nitrogen. Carbon is less electoral negative than nitrogen, since nitrogen is more electro negative, it would be here on this side and carbon would be here on this side and since nitrogen is more electro negative, that explains why its atomic orbital are lower in energy. See here, it's two p orbital czar also lower in energy, carbons are higher in energy. And then here if you look at oxygen to neon, same thing. This two s orbital atomic orbital is higher in energy than this one, meaning the left side is involved with an element that has less electro negative. So for example maybe we have here um oxygen versus flooring. Okay so keep in mind that electro negativity helps us determine which molecular orbital diagram to use. And also it helps us to see the differences in energy for our atomic orbital's. Now. Just remember that the higher your electro negativity then the electrons will be closer to the nucleus so they're more tightly bound to the nucleus. Okay. What effect will this have on our shell number here? So here are electrons are being pulled closer and closer to the nucleus and electron activity is increasing. Uh This will see a lot of the times with lower numbered shell elements such as flooring. So here we have a lower shell number. Alright so keep in mind these fundamental ideas. We're talking about hetero nuclear di atomic molecules and Emma theory.