In this video, we're going to introduce the octet rule. Now, the octet rule is really just a rule of thumb that says that atoms are more stable and less reactive when their valence shells are fully occupied. Recall from our last lesson video that the first energy shell will hold up to a maximum of just 2 electrons, but the second energy shell will hold up to a maximum of 8 electrons, and really, this 8-electron maximum is where this octet is coming from with the octet rule. Most of the simple atoms that we'll be talking about in our biology course are going to apply to this octet rule. But really, the main takeaway here of the octet rule is that atoms are going to be less reactive when their outer valence shells are fully occupied.
So let's take a look at our image down below to get a better idea of this octet rule. Notice that here in the middle what we have is an electron; these little blue circles that you see throughout our image represent electrons. This represents some electron that wants to react. What you will see is that on the left we have an atom and on the right, we have another atom, and so what you'll notice is that the dinner table here, with the Thanksgiving turkey, represents the nucleus of these atoms, and then, revolving around the nucleus what we have are the electrons. We're specifically focusing on the second energy shell here, which we know holds up to a maximum of 8 electrons. Notice that the electrons that have an open slot in their energy shells are going to be more likely to react. You can see that this atom over here, because it does have an open slot that's available, says "yes, there is a spot for you here," and so it will react with other electrons from other atoms. However, this atom over here notice has a full octet of electrons and because it is full it says "nope, we're full," and they do not react with other electrons from other atoms. The idea once again is that atoms are going to be less reactive when their valence shells are full. Like this one has a full octet in its second shell, so it's going to be much less reactive and it will not react with other electrons that want to react. That's the main takeaway here of the octet rule, and we'll be able to get a little bit of practice in our next few videos. So I'll see you guys there.