Electron Shells

Electrons

Electrons occupy shells. *insert crap turtle joke*. These shells are what the electrons orbit the nucleus on. Simple. Fills the lowest energy cells first, then the larger ones. Might seem a bit confusing...

So the amount of electrons that can fit in a shell goes in this pattern:

2,8,8

You actually don't need to know any further than that. Good isn't it? So, 2 electrons in the first shell, then 8 in the next and then 8 in the next. Can it get any simpler? Well I can try. If you had a doughnut and it had jam in the middle it would start in the middle and go outwards. No one want to find the middle without jam, you do? Freak.

Ignore the extra 2. No one cares about it.

So the electron shells fill up from the closest shell that can fit 2 electrons to the outer shells that can fit 8. The name for this is "Electronic Configuration". You do need to know this, don't start slacking now.

In the exam, that word hurts so much, you might be asked to draw or work out the electronic configuration of any of the first 20 elements in the periodic table. Sure, you could spend all that time learning them off by heart or just keep it simple like this:

Let's take Magnesium. It has 12 protons. 12 protons = 12 electrons. So 2 in the first shell, that leaves us with ten and then 8 in the next and that leaves us with 2 and 2 in the final, but not full, shell. 

The electronic configuration of Magnesium is: 2,8,2. 

OR

2,8,2

So, simple stuff.