In this video, we're going to introduce the octet rule. The octet rule is really just a rule of thumb that applies to most of the simple atoms that we're going to discuss in our biology course. The octet rule states that atoms are more stable and less reactive when their valence electron shells or their outermost electron shells are fully occupied. Recall from some of our previous lesson videos that the first energy shell of an atom holds up to 2 electrons, but the second energy shell of an atom holds up to 8 electrons. This 8 here is where the octet rule gets its name since "oct" is a root that means 8. The main point of the octet rule is that atoms are going to be less reactive when their outer valence shells are fully occupied or when they are full.
If we take a look at our image down below, we have this interesting analogy for the octet rule. You'll notice we have a bunch of blue circles all around, and these blue circles represent electrons. Notice that over here on the left, we have one atom, and over here on the right, we have a second atom. At the center of the atom, what we have is this turkey, and the turkey represents the nucleus of those atoms. It's almost as if these electrons are sitting at a dinner table, surrounding the nucleus of the atom.
Notice here in the middle, what we have is a single electron here that's asking, "Hey, want to react?" This atom over here on the left only has a total of 7 electrons. Recall that the second energy shell holds up to 8 electrons, so this atom does not have a full valence shell. It has one open slot, or you can think of this as one open seat at the dinner table. Notice that the electron is saying, "Yeah, there's a spot for you," and that spot again is this open spot that you see here, so because this atom does not have a full valence shell, it can react. Notice that we have a green check mark here to indicate that this electron would be able to react with this atom.
Notice over here on the right-hand side, this atom has a full valence shell with 8 electrons in its outermost shell. It does not have any spots open, and it says, "Nope, we are full," so notice we have this red X here to indicate that this electron would not be able to react with this atom. Once again, the main takeaway of the octet rule is that atoms are going to be less reactive when their valence shells are full, and this one has a full valence shell and does not react.
This here concludes our brief introduction to the octet rule, and we'll be able to get some practice applying these concepts as we move forward. So, I'll see you all in our next video.
