Electronic Configuration for d-block elements [ENDORSED]

[Andrew Nguyen 2I]

I've noticed after doing some of the problems that the d-block elements fill up the orbitals in the d-block before the previous s-block, which goes against certain patterns from before. Is this a correct observation and if so, could someone explain why this occurs?

[Chem_Mod]

Your observation is correct. After atomic number 20, there is enough shielding that the 3d orbitals have a lower energy than 4s.

[Naveed Zaman 1C]

The same thing happens for f-orbitals, although to a greater extent. Technically the d-orbitals are open in the 3rd energy level (which is why some elements break the octet rule in bonding), but they are not usually occupied until you have gone through the 4s orbitals. Hope this helps!

[Kathleen Vidanes 1E]

Why is it that we use Px, Py, and/or Pz when writing the electron configuration for p-block elements,but not d-block elements?

[Kevin Ru 1D]

Hi! The reason why the nodal planes are different once you reach the d orbital is because there are more orbitals. While p has 3 orbitals, d has 5 orbitals of a given energy.

[Joshua Xian 1D]

For the electron configuration exceptions in the d-block, why is tungsten not an exception (it is [Xe]4f14 5d4 6s2 instead of [Xe]4f14 5d5 6s1) while elements in the same group (chromium and molybdenum) are?

[Joshua Xian 1D]

Also, why are most of the 4d elements exceptions, and why is platinum an exception?

[Sohini Halder 1G]

It is because of the shielding effect. The electrons with the highest energy, and therefore least bound to the nucleus, will be removed first. That's why we write the d block elements first, to represent that the last electrons are the ones that will be removed.

[Lauryn Jordan 1F]

So for elements after 20 would you fill up the 4s and then return back to 3d or fill up 3D and then proceed?

[Chem_Mod]

That is correct. However, remember that Mn, Cu, Cr, and Ag are exceptions. In these cases, it is easier to fill the 3d orbital (instead, there would only be one electron in the 4s orbital, while the other electron would be in the 3d. This was discussed in class today.)