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