[NewtoAtoms]

Hello Chemists,

I am studying for my Chemistry final and I have stumbled across a problem, which I do not understand.

I understand that electron configuration follows a chart, therefore there is a very specific way to fill electrons

1s - 2s - 2p - 3s - 3p - 4s - 3d - 4p

Therefore if I am asked to write the electron configurations of Cu I would write

1s2 2s2 2p6 3s2 3p6 4s2 3d9  BECAUSE according to the chart, 4s orbitals fill before 3d orbitals....

HOWEVER this is wrong.

the correct answer for copper is 1s2 2s2 2p6 3s2 3p6 4s1 3d10

WHY OH WHY???  I thought 4s is before 3d...

Can someone explain please.

Thank you so much for your time and help.

New to atoms

[Schrödinger]

First thing you need to remember : There are always exceptions to rules

http://www.science.uwaterloo.ca/~cchieh/cact/c120/eleconfg.html
Read the topic 'Special Electronic configurations'