Atomic Structure: Valency

So remember in the last post when we talked about ELECTRON SHELLS? Remember that they could have many many many shells, and yet a maximum number of electrons in each shell? If you don't it's okay, we'll recap.

So basically, the way electrons are arranged in an atom is also called electronic configuration. If you want to represent it visually, it'd look like this:

If you want it in orbital notation it'd look like this:

I would continue with spdf and all but that's for another day. ANYWAYS...

The circles you see with the x's on them? That's called a shell. And those x's are electrons. So the first shell can hold up to 2 electrons and the second and subsequent ones can hold up to 8 electrons. Now, now, here's the complicated part.

A VALENCE ELECTRON is an electron that lies on the outermost shell of an atom. The outermost shell is also called the "valence shell". So what is this complicated "valency"?

Valency --> No. of electrons needed to be gained or lost to complete the shell

"Complete the shell?" Simi lanjiao. 

"Completing the shell" means making the shell is full. So for example, iodine, has seven valence electrons yes? To complete the shell, you need to gain another electron, to ensure you have the maximum number of electrons in the shell (8).

Here's the complicated part. Sometimes an ion will also lose electrons to complete the shell. In the case of lithium for example, a lithium ion has only one valence electron. So what does it do to complete the shell? It loses that electron. 

Why does it do that? Because losing one electron is easier than gaining seven more. (informal answers you must not use in exam) BUT YES, VALENCY IS COMPLICATED. So here's a little valency table for you:

Things to note:

Down the group, elements all have the same number of valence electrons. 

However, number of valence shells increase down the group.

Across the period, number of valence electrons increase

Why does all this happen? Moving on to electron affinity...