Why does the 4s sub-shell fill before the 3d sub-shell

[Mcat35]

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I know you can just read it off the periodic table, but I'm not understanding why. Or is that beyond MCAt scope.

http://commons.wikimedia.org/wiki/File:Electron_shell_019_potassium.png

for that picture of Potassium, the 4s electron would be the valance electron right? Before the 3Ds fills.


Thanks

 

[golgiapparatus88]

I know you can just read it off the periodic table, but I'm not understanding why. Or is that beyond MCAt scope.

http://commons.wikimedia.org/wiki/File:Electron_shell_019_potassium.png

for that picture of Potassium, the 4s electron would be the valance electron right? Before the 3Ds fills.


Thanks

The 4s shell is actually at a lower energy level and thus, fills first. On the other hand, 3d electrons are released first when an electron is removed.

The easiest way to see this is by using the n+l rule.
Take 4s, n=4 and l=0, 4+0 = 4
Take 3d, n=3 and d=2, 3+2 = 5.

4<5 so 4s will fill first! When I learned the n+l rule, i went "OHHHHHHHHHHHHHHHHH" 😀

 

[Mcat35]

The 4s shell is actually at a lower energy level and thus, fills first. On the other hand, 3d electrons are released first when an electron is removed.

The easiest way to see this is by using the n+l rule.
Take 4s, n=4 and l=0, 4+0 = 4
Take 3d, n=3 and d=2, 3+2 = 5.

4<5 so 4s will fill first! When I learned the n+l rule, i went "OHHHHHHHHHHHHHHHHH" 😀

ok cool rule. The valance would be d electrons on 3d right? therefore it comes off first. with exception to the half filled valence elements or the full filled valence elements?

 

[golgiapparatus88]

ok cool rule. The valance would be d electrons on 3d right? therefore it comes off first. with exception to the half filled valence elements or the full filled valence elements?

Actually, for transition metals the valence is everything in the outer shell. So Nickle for example has a configuration of [Ar] 4s2 3d8 so it has a total of 10 valence electrons. Just like carbon has 4 valence electrons (2 from s and 2 from p).

I actually misspoke about which electrons come off first. (It's been a while since I reviewed this). The "s" electrons come off first before the d electrons for the same reason that "s" electrons are filled before "d" electrons. For example, Cu is [Ar] 4s1 3d10 while Cu+ is [Ar]3d10.

 

[Mcat35]

Actually, for transition metals the valence is everything in the outer shell. So Nickle for example has a configuration of [Ar] 4s2 3d8 so it has a total of 10 valence electrons. Just like carbon has 4 valence electrons (2 from s and 2 from p).

I actually misspoke about which electrons come off first. (It's been a while since I reviewed this). The "s" electrons come off first before the d electrons for the same reason that "s" electrons are filled before "d" electrons. For example, Cu is [Ar] 4s1 3d10 while Cu+ is [Ar]3d10.

ah ok cool. thanks

 

[golgiapparatus88]

ah ok cool. thanks

no problem 🙂