Valence Electron Predictions

Valence Electrons!

As you may recall from previous science courses, valence electrons are the electrons that are on the outermost energy level of an atom.

Valence electrons are the ones that take part in chemical reactions. The more unstable an atom is, the more likely it will gain or lose electrons to become stable.

Take a neutral sodium atom, for example. It has eleven electrons, two on the first energy level, eight on the second, and one on the last one. Sodium in this case has an open shell, because its outermost shell is not completely filled.

How how sad it is, to be that lonely little valence electron hanging out all by itself! Poor little particle! Won't anyone love him for who he is? He just wants to be LOVED! He doesn't need much at all, really, just someone out there to care for him, and he'll care for them in return too! Um...*cough* I mean...okay, anyway...moving on...

Noble gases do not gain or lose electrons easily. This is because they typically have closed shells, which mean that their outermost shells are filled up.

Take argon, for instance. See how all the available spaces are taken up by electrons?

Writing Core Notation to Figure out the # of Valence Electrons

Here's a trick for writing electron configurations that can save you a lot of time. Let's say you're writing the configuration for an ion of manganese - Mn ²⁺ .

A neutral atom of Mn has 25 electrons, and Mn²⁺  will have 23, since it lost two to gain a +2 charge. The electron configuration of Mn²⁺  will be 1s²2s²2p⁶3s²3p⁶4s²3d³

Now look closely at the noble gases. Notice how the first part of the configuration of argon (1s²2s²2p⁶3s²3p⁶) is the same as Mn²⁺. In this case, we can substitute the first part of Mn²⁺   that contains all the same configuration as Ar for the notation of Ar itself!

So now we have [Ar]4s²3d³.

To find all the valence electrons, count up the # of electrons that was NOT included in the core. Do NOT count filled d- or f- shells.

Mn²⁺  has 5 valence electrons. Amazing!

Looking for further help? Check out this informative website!

Complete Electron Configurations