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Electron Configuration - Concept

Teacher/Instructor Kendal Orenstein
Kendal Orenstein

Rutger's University
M.Ed., Columbia Teachers College

Kendal founded an academic coaching company in Washington D.C. and teaches in local area schools. In her spare time she loves to explore new places.

Electron configuration is shorthand for the arrangement of electrons in atomic orbitals. It is written out, as opposed to orbital diagrams which are depicted pictorially. For elements with many electrons, noble gas configuration is a useful way to abbreviate the electron configuration.

Alright let's talk about electronic configuration. Electronic configuration is the arrangement of electrons in an atom. So before we talked about orbital diagrams and up here we actually have a bunch of orbital diagrams, but instead of having to write all of this out to describe where electrons go and how they fit into the atom we're actually going to make it shorthand and that way we're going to do electronic configuration. So let's start with neon, we know neon has 10 electrons in its neutral state so, and when I do the orbital diagram this is what I got with 10 electrons drawn out. Instead of having to draw all of that out, I'm going to do a shorthand version and say okay in that 1s orbital we have two electrons so I'm going to make a superscript of 2. In the 2s orbital, I have 2 electrons again the superscript of 2, in the 2p orbital or sublevel I have 6 electrons so I'm going to make a superscript of 6. So this is basically electronic configuration.

Alright so let's do something a little bit more complex, lets do sodium. Sodium has 11 electrons in its neutral state, so okay so awesome, we're going to say this has 1s2, 2s2, 2p6, 3s1. Well there's something special about neon, neon we know it's a noble gas meaning all the electrons are filled in the outer of shell. So this makes it a special kind of atom or element, so down here this is one more electron than sodium, so instead of having to rewrite this whole thing, notice that this electronic configuration is identical to this one, there're the same. So instead of writing this again the whole thing I can just write it well sodium has the same electronic configuration as neon plus a 3s 1 electron easy enough.

Okay let's take chlorine which has a little bit more electrons, chlorine if we just simplify this into electronic configuration we'd say okay chlorine has a 1s2, 2s2, 2p6 again same as neon so instead I'm going to just write neon, 3s2, 3p7 so this is the electronic configuration for neon. And we're going to call these two, this one and this one the noble gas configuration. Okay so which is the same thing as electronic configuration just a little bit shorter and easier to write, easier to manage. But what if we come across an element that has 87 electrons such as francium, that has a ton of electrons and I don't want to have to draw all of this out. This is such a pain, so an easy way to do this, is if you look at the periodic table, here is francium right here, the noble gas before francium is radon, radon has 86 electrons, francium only has one more. So we're going to say okay let's make it easy on ourselves let's say it has one more electron awesome. So I just have to notify or notice where is the electron coming from and where is, how I'm I going to denote that? So francium we know is in the seventh period, so we're going to say okay great. Let's actually go and put 7 there, and everything in group 1 ends in an s1 so we're going to say okay great 7s1.

If we're going to talk about something let's say, let's look at sulphur, sulphur notice it's in the third period so the noble gas configuration will be neon 3s and then we go over to the p's 1, 2, 3, 4 p4. So sulphur we're going to write it 16 electron it will be, what did we say neon? 3s2 we don't forget we have to denote that 3p4 pretty much easy enough. That is electron configuration and noble gas configuration.