Can someone please give me a quick explanation of noble gas electron configuration?

It's the ion ones that confuse me, but the regular atom ones do, too.

2 Answers
Dec 2, 2016

The outer (valence) shell is completely filled with all possible electrons, making it very stable and nonreactive.


Electron configuration is just the description of how many electrons are in each orbital. Elements are “built up” by the addition of protons and electrons in a regular sequence that we portray as the Periodic Table.

The “noble gases” were called that in historical chemistry because of their stability – they do not react readily with other compounds. This is because their outer (valence) electron shell or orbital is completely filled, making it very stable. It neither wants to give up an electron nor take more on, as in each case it takes more energy to do that than to remain in its normal state.

Other elements in their normal state contain unfilled orbitals in their valence shell, making them react with other suitable elements to form more energetically stable compounds. Starting from the “ground state” (normal condition) of any element we can determine whether adding or taking away electrons will more quickly bring it to a more stable state.

Dec 10, 2016

It's essentially a shorthand, to help you keep your electron configurations from getting too long.


To illustrate this, let's try an example:

Write the electron configuration of Selenium, Se.

Answer: #1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^4#

That is pretty long! And especially as you keep doing lots of these examples, you'll find that you have to write lots of the same things again and again. So, to save time, here's what we do. We substitute in the nearest noble gas for most of the configuration. Let me show you how this works:

This diagram depicts everything you'll be writing in the original electron configuration of Selenium above:

enter image source here

Now, if we take into account the configuration of the Noble Gas closest to Selenium - Argon - here's what we have:

enter image source here

So as you can see, what we're doing is we're substituting in the Noble Gas's Electron Configuration for most of the actual element's electron configuration.

Now, let's write the electron configuration of Selenium with Noble Gas electron configuration:

#[Ar] 4s^2 3d^10 4p^4#

Notice how we saved a lot of space with that. This will help you save some time when writing out configurations, especially if you have to do many of them.

As for ones with ions, that's just a matter of adding or subtracting based on the number of electrons lost/gained. So, for example, if you had a +2 ion, then ask yourself: have I lost or gained electrons? In this case, you've lost 2 electrons. This means that you'd take the original electron configuration of that element, and subtract 2 electrons.

Hope that helped :)