Explain Energy Level Split for Two Atoms

[anhnha]

Hi,
can anyone help me explain more detail about energy level split with the system of two atoms?
Please see this video at 06:32:http://www.youtube.com/watch?v=y_GZn4o8gaE
Thank you.

 

[anhnha]

Haha, I have just seen the answer:
Consider 2 atoms of copper. So now we will think of this as a single two-atom system and not as a system with 2 atoms in it. This system now has 58 electrons(not 28 electrons in two atoms). How do we fill these electrons in the sub-shells?The 1s subshell can only accommodate 2 electrons. But we want that it should have 4 e's. So each energy level of the isolated atom splits into two levels for the two-atom system. Thus 4 e's can now be accommodated in the two levels of the 1s sub-shell.