Re: Please explain the electron configuration of palladium.

Hello the enigmatic Mr. or Ms. L,

“er. sorry I have been a bit lazy in answering this question. I hope you 
have remained sane while waiting for my response.”
| -) (that smiley is meant to be sleeping)

I was wondering about Palladium’s odd quality of and 5s^0 shell a 
while ago and never found the answer specifically. I think I know why 
this is said to be the case though. It is more of a reminder that the 
shell is there rather than a strange feature of palladium. I have seen 
the electron arrangement quoted without the 5s shell. However, the 
reason why some people leave the shell there is probably this...

My Chemistry teacher used the analogy of a chest of drawers when 
explaining quantised energy levels in atoms. You can only put your 
clothes (if electrons are what you like to wear) in one drawer or 
another. Try putting a (whole) shirt in both the second and third 
drawers and you’ll know what I mean. The same is true for electrons 
(at the moment anyway - some guy says he can split them with liquid 
Helium [??]). If you had a chest of drawers in which you only filled the 
first three drawers but it had six in total, the others would not cease to 
exist, they would just be empty.

So is the 5s shell in Palladium. Its there and usable but Palladium 
keeps a spare drawer for electrons when other atoms “spend the 
night” (I may be taking the analogy a bit far here!). As the 4d and 5s 
shells are so close energetically it is fairly easy for palladium to move 
electrons into the 5s shell. The 5s will actually have been filled up in 
atoms of lower atomic number in the same period (eg: Strontium [Kr] 
+ 5s^2) because a full 5s shell is more stable than a partially filled 4d 
shell. However for Palladium a filled 4d shell is favourable. In 
reactions the 5s shell can be used to store electrons temporarily.

I think that is why the 5s^0 is mentioned in sometimes. However, I 
have seen periodic tables labelling Pd without the 5s^0.
I don’t think it is true that valence electrons can only be in the s and p 
shells though as this would make most compounds involving 
transition metals impossible (if I understand you correctly).

I hope I have cleared this up for you but now I am wondering why 
nickel has the configuration [Ar] + 4s^2 3d^8 and platinum is [Xe] + 
6s^1 4f^14 5d^9 ! Probably to do with energy levels...

there y’ go, if it ain’t good enough, ask MadSci.net again,
Paul Henderson

Dan Berger adds:
Electrons in the 4d subshell of palladium are also "valence electrons" 
because they are high enough in energy to participate in bonding, even 
though they formally belong to a non-valence shell.