There are three important pieces of information you will need to complete the Electron Configuration Worksheet from yesterday’s lesson.

1. Tricks

Lets do the Electron Configuration for ₅₇Ce. It would look like this:

Because ‘La‘ comes before ‘Ce‘, we have to add the 5d¹ before we start counting the 4f orbital.

Now if we did the Electron Configuration for ₇₂Hf, which is next to La, we have to go entirely through the 4f orbital before we go back to the 5d.

BUT! When we do this, it would not make any sense to write 5d¹ 4f¹⁴ 5d²…

SO… we combine the 5d’s and place them after the 4f

2. Ions

Simple… if it’s a (-) then you add electrons to the final orbital.

₉F is 1s² 2s² 2p⁵
₉F^-1 is 1s² 2s² 2p⁶

If its a (+) then you subtract electrons from the final orbital(s).

Na is 1s² 2s² 2p⁶ 3s¹
Na⁺ is 1s² 2s² 2p⁶           The 3s orbital has been lost!

3. Shorthand

This is the shortcut so you do not have to write out those huge-mungous (yes that is a word) electron configurations.
Lets do the electron configuration for Cl.

₁₇Cl 1s² 2s² 2p⁶ 3s² 3p⁵
The shorthand version uses the MOST RECENTLY PASSED NOBEL GAS (so when you pass gas use the shortcut… get it… c’mon that’s funny!) So for Cl, the most recently passed gas is Ne. So instead of starting at our ‘House’ (H), we’ll start at Ne and then count the orbitals from there.
₁₇Cl [Ne] 3s² 3p⁵