Electron shells

[almostdonewithschooling]

Hey guys,

I got my chem headstart booklet a month ago and it said to draw an electron shell diagram for calcium. 

Do I use the 2-8-18-32 method or the 2-8-8-18?

Thanks x

[Sine]

Hey guys,

I got my chem headstart booklet a month ago and it said to draw an electron shell diagram for calcium. 

Do I use the 2-8-18-32 method or the 2-8-8-18?

Thanks x

calcium is 2-8-8-2

We start to fill the 4th shell up since the 4s shell is of a lower energy level than 3d.

continuing on Scandium (21) is 2-8-9-2

[almostdonewithschooling]

But when do you actually use the 2-8-18-32 method though?

[keltingmeith]

But when do you actually use the 2-8-18-32 method though?

Never. It's a shit method that's stupidly simplistic and breaks down the moment you consider atoms past calcium. This is also why in school you only ever talk about elements with atomic number of 20 or lower (also potentially why your school told you memorise the first 20 elements).

If ever asked to state the electronic configuration, you should always use the sub-shell method. It's not slower than the 2-8-18-32 method, is more descriptive and actually correct, and works for every element.

EDIT: in fact, sorry, it breaks down before calcium - last one it actually works for is argon.