GC: Electron Configuration - Valence electron removal question?

[Member 8586]

So

Fe 26 atomic number, 56 mass number - 1s2 2s2 2p6 3s2 3p6 4s2 3d6
Fe2+ 26 atomic number, 56 mass number BUT +2 charge so 1s2 2s2 2p6 3s2 3p6 3d6

in the Fe2+ the two 4s2 electrons get removed instead of two of the 3d6 electrons.

In my notes, I have written "always remove from valence shell, which is the outer shell, which is the shell with the highest number.... But I also have something written about Transition Metals.... Is this rule only for transition metals Groups 3-12 or for everything??

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[ttpharm]

You remove it from 4s because its higher energy than 3d

 

[Member 8586]

You remove it from 4s because its higher energy than 3d

yeah i get that part, but does that apply to all elements? or only transition elements?

also, so electrons fill orbitals in a different order that they leave orbitals then?

 

[Member 8586]

bump?

 

[GoBlue24]

yeah i get that part, but does that apply to all elements? or only transition elements?

also, so electrons fill orbitals in a different order that they leave orbitals then?

A1) The general rule is that, as ttpharm mentioned, you remove electrons from the highest energy level always. ALWAYS. It doesn't matter what element... just know that rule always applies. The only reason this rule is really important, though, is for removing electrons in transition elements because their electron configuration is "abnormal". They have electron configurations with a higher energy level subshell that fills before a lower energy level subshell (4s before the 3d, 5s before the 4d, etc) as you probably know already.

So if you did it "normally" like non-transition elements, you would remove electrons from the end of the electron configuration like Ca2+ and it would be 1s2, 2s2, 2p6, 3s2, 3p6 since the 4s2 electrons at the end are removed. BUT since Fe's 4s subshell get's filled before it's 3d subshell... the configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d6 and if you wanted to get Fe2+, using the logic of removing electrons from the end of the electron configuration, you would get 1s2 2s2 2p6 3s2 3p6 4s2 3d4 which is WRONG. Always remove from the highest energy level. If the subshells are in the same energy level, remove from the highest subshell energy level.

A2) Yes, electrons fill in a different order than when they are removed for the 3s/4d subshells, 4s/5d subshells, etc. As electrons fill, the energy levels change. The reason 4s subshells get filled before 3d subshells is because it is at a lower energy level than the 3d subshells to start off with. As 3d subshells become filled, it's energy level becomes lower than the 4s and so now 4s has the higher energy level (and is removed first now). If you look on an energy/orbital diagram... you can see that the 4s and 3d are almost exactly at the same level. A small change makes one subshell have a higher energy level than the other.

 

[Member 8586]

A1) The general rule is that, as ttpharm mentioned, you remove electrons from the highest energy level always. ALWAYS. It doesn't matter what element... just know that rule always applies. The only reason this rule is really important, though, is for removing electrons in transition elements because their electron configuration is "abnormal". They have electron configurations with a higher energy level subshell that fills before a lower energy level subshell (4s before the 3d, 5s before the 4d, etc) as you probably know already.

So if you did it "normally" like non-transition elements, you would remove electrons from the end of the electron configuration like Ca2+ and it would be 1s2, 2s2, 2p6, 3s2, 3p6 since the 4s2 electrons at the end are removed. BUT since Fe's 4s subshell get's filled before it's 3d subshell... the configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d6 and if you wanted to get Fe2+, using the logic of removing electrons from the end of the electron configuration, you would get 1s2 2s2 2p6 3s2 3p6 4s2 3d4 which is WRONG. Always remove from the highest energy level. If the subshells are in the same energy level, remove from the highest subshell energy level.

A2) Yes, electrons fill in a different order than when they are removed for the 3s/4d subshells, 4s/5d subshells, etc. As electrons fill, the energy levels change. The reason 4s subshells get filled before 3d subshells is because it is at a lower energy level than the 3d subshells to start off with. As 3d subshells become filled, it's energy level becomes lower than the 4s and so now 4s has the higher energy level (and is removed first now). If you look on an energy/orbital diagram... you can see that the 4s and 3d are almost exactly at the same level. A small change makes one subshell have a higher energy level than the other.

awesome! thanks for clearing that up