Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I have been taught in school that atoms cannot have more than 8 electrons in the outer shell. Palladium atom's electron configuration is 2,8,18,18. Why isn't it 2,8,18,17,1 like the case of Platinum 2,8,18,32,17,1 or Nickel 2,8,17,1 and they are all in the same group?

share|cite|improve this question
up vote 8 down vote accepted

As suggested by M.Sameer I convert my comment into an answer:

Dear M.Sameer: It seems that you are missing that the $n+\ell$ Madelung rule is not an exact result derived from first principles, but rather a rule of thumb, that holds for, say, approximately 95 percent of all the elements, with important exceptions, cf. this wikipedia page. Nevertheless, there are semi-rigorous theoretical arguments why such a rule of thumb should hold to a good approximation.

share|cite|improve this answer

all d-block elements will have their last electron in 'd' orbital. thus even if it is in the 5th period it has no 5th shell as it first fills the 'd' block in 4th shell

share|cite|improve this answer
That isn't true. The $5s$ orbital (usually) has a lower energy than the $4d$, so electrons will start filling the $5s$ orbital before they start filling the $4d$ orbital. – John Rennie Feb 28 '15 at 6:42

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.