Jumps within Electron Configurations

[MitsuZero]

I was wondering what was the reason that electron configurations seem to arbitrarily change between elements. To be more precise, while brushing up on the some basics with the periodic table, I noticed the fact that as you progress across a row [and the subshells are filled] electrons jump between different subshells for no apparent reason (not apparent to me, in any case).

For example, between Nickel and Copper:
Ni: [Ar] 4s2 3d7
Cu: [Ar] 4s1 3d10
The 4s subshell lost an electron to help fill the 3d subshell. Why did it choose to let it go now? Why not sooner, or later in the periodic table?

An even better example is between Zirconium and Niobium
Zr: [KR] 4d2 5s2
Nb: [KR] 4d4 5s1
The 5s subshell again lost an electron to help further fill the 4d subshell (which still has a long way to go before it is filled).

Again, I'm confused as to why the electron jumped out of the 5s subshell for the 4d subshell. It's not as if the 4d subshell was even close to filling it's shell.

Anyways I'm currently studying upper division quantum mechanics, so I wouldn't mind a slightly loaded answer.

Thanks in advance.

 

[Jhero]

Thank you for your question about electron configurations and their apparent changes between elements. I can explain this phenomenon using principles from quantum mechanics.

First, it is important to understand that electrons do not move in a predictable and orderly manner like planets around the sun. Rather, they exist in a state of constant uncertainty and can occupy different energy levels or subshells within an atom. This is known as the Heisenberg uncertainty principle.

Now, moving on to your specific examples: in the case of Nickel and Copper, the electron configuration changes because it is more energetically favorable for the 3d subshell to be completely filled than for the 4s subshell to have two electrons. This is due to the fact that the 3d subshell has a lower energy level than the 4s subshell. This phenomenon is known as the Aufbau principle, which states that electrons will fill lower energy levels before higher ones.

In the case of Zirconium and Niobium, the electron configuration changes because the 4d subshell is actually closer to being filled than the 5s subshell. This is due to the fact that the 5s subshell has a higher energy level than the 4d subshell. Again, this follows the Aufbau principle.

It is also important to note that as we move across a row in the periodic table, the number of protons in the nucleus increases, resulting in a stronger nuclear charge. This causes the energy levels of the electrons to shift, leading to the changes in electron configuration that you have observed.

In summary, the changes in electron configuration between elements are not arbitrary, but rather follow the principles of quantum mechanics and the Aufbau principle. I hope this helps to clarify any confusion you may have had. Feel free to ask any further questions.