Hi, as an atom's Z number increases its size different energy levels of electrons appears. As the electrons are filled in an atom we see that the 4s orbital is being filled before the 3d orbital. Then when we take away electrons from transition metals, the 4s orbital electrons goes away first then the 3d's are removed.
In my attempt to understand this weird phenomenon I have come across an article by Eric R. Scerri who is a chemist at the University of Purdue. This criticism of Atkins textbooks states that even though at a basic level we learn in general chemistry that the reason why 4s is filled before 3d is because 4s is lower in energy than in 3d this is infact false because 4s never is lower in energy than 3d (http://www.chem.ucla.edu/dept/Faculty/scerri/pdf/Atkins_critique.pdf
- beginning of page 6).
So now my two questions are why does the 4s orbital is being filled before the 3d one and why are the 4s electrons are removed before the 3d one.
If this article is wrong and 4s is indeed really lower in energy than 3d then the first answer is easily answer with Hund's rule but then the second question takes all it's importance, if on the other hand the article is right about the 4s and 3d energy level then the first question becomes hard to answer and the second one is answer by a '' because the 4s electrons have more energy than the 3d''.
Anyhow ignore the last paragraph if it confused you
Thanks a lot for your help,
By the way, my knowledge of Schrodinger Equation's and Wavefunction is fairly low because I never learned that in class yet, I only know these from layman book's Ive read about quantum mechanics so if you can give me a good explanation that doesn't require the mathematical parts I'll be happy and wait till I learn everything to understand it mathematically!