With a Lewis structure, and it might look something like this, where oxygen has one, two, three, four, five, six valence electrons, and you might say, hey, it would be nice if oxygen somehow were able And so in this situation, you say, okay, oxygen has six valence electrons, and oftentimes that's drawn Least a filled SNP subshells in their outer shell. Now, why is six valenceĮlectrons interesting? Well, atoms tend to be more stable when they have a filled outer shell, or in most examples, at Generally aren't reactive, or aren't involved as much in reactions? It has two core, two core electrons. And how many core electrons does it have? And the core electrons In the outermost shell? You have six electrons here. So the outermost shell is beingĭescribed right over here, this second shell. How might oxygen react, it's interesting to look at Up all the electrons here, I have exactly eight electrons. So I have four right now, I have to have four more, so then you're going to have 2p4. Well, in a neutral oxygen atom, you have eight protonsĪnd eight electrons, so first you're gonna fill the one shell, then you are going to startįilling the second shell, so you're gonna go 2s2, So oxygen's electronĬonfiguration is what? Pause this video and see if And so just to make that point, or make it a little bit clearer, let's look at the electron configuration of an element that we'll Or how a given element is likely to react with other atoms. Is, what is the point? And the point of electronĬonfigurations is, is they can give us insights as to how a given atom Might have been asking yourself this whole time that we've been looking at electron configurations We are now going to talk about valence electrons, and non-valence electrons, whichĪre known as core electrons and so one question that you Once you reach the fourth period and the transition metals they follow an 18 electron rule of stability, but it's the same idea as before in that they are attempting to fill their valence electron shells in order to become stable. This octet rule holds for elements in the second and third periods (or rows) of the periodic table. This need to gain a filled valance electron shell by having 8 valence electrons is known as the octet rule and explains why certain elements are stable or unstable despite being electrically neutral. Neon has 8 valence electrons which is a filled second electron shell and is therefore stable and will be unreactive since it does not need to take electrons from other atoms. And again this can be explained by neon's valence electron configuration which is: 2s^(2)2p^(6). Now if we take a neutral atom of neon, Ne, which is just to the right of fluorine, neon is practically the opposite of fluorine in terms of reactivity despite both being neutral atoms. In other words, it will react in such a way to gain a new electron and fulfill its valence shell.

And since it's so close to being filled, it will desperately want an extra electron which it will take from any nearby atom to do so. But fluorine has 7 valence electrons, 1 away from being filled. The second electron shell holds a maximum of 8 electrons and 8 electron would be considered a filled valence shell and would therefore be stable and unreactive. And this is explained if we look at fluorine's valence shell (the second shell) electron configuration: 2s^(2)2p^(5). For instance, if we take an atom of fluorine, F, in it's neutral state it has no net charge however it is VERY reactive. So even if an atom is neutral, that is not necessarily its most stable state.

And vise versa, something which is unstable is reactive and will engage in chemical reactions to reach a new state. Stability meaning that something is unreactive, that it won't engage in some kind of chemical reaction to reach a new state. The valence shell meaning the outermost electron shell. So being stable when talking about valence electrons means that the valence shell has been filled completely (or half filled).

Valence electrons on a periodic table