Page 1 of 1

3d and 4s

Posted: Mon Oct 23, 2017 11:12 pm
by Mike Matthews 1D
Could someone please explain to me when 3d is filled before 4s and when it is not. I'm very confused about this. What are the exceptions to the rules regarding 3d and 4s? Also could someone explain to me why the electron configuration of Titanium is [Ar]3d24s2 instead of [Ar]3d4. Thank you.

Re: 3d and 4s

Posted: Tue Oct 24, 2017 4:07 am
by soniatripathy
The 2 exceptions to e- config. that you need to know for this class are Chromium and Copper. The 3d will "rob" one electron for the previous subshell to make it less reactive. This occurs because a half filled subshell is the second most stable e- orientation (after a filled subshell).

Re: 3d and 4s

Posted: Tue Oct 24, 2017 10:29 am
by Nicole Nikolov 1K
Generally, the 4s orbital will be filled before the 3d orbital, because 4s is of lower energy than 3d. If you follow the fourth period of the periodic table from left to right, you see that 4s gets filled before 3d. However, two exceptions to this in the fourth period are chromium and copper: these two elements will steal an electron from the 4s orbital. This happens because chromium is one electron from having its d-orbital half-filled, and copper is one electron from having its d-orbital half filled. The reason behind this is that a atom with a half-filled/filled d-orbital and partially filled s-orbital is more stable than an atom with a filled s-orbital and a partially filled d-orbital.

Re: 3d and 4s

Posted: Tue Oct 24, 2017 11:26 am
by Eli Aminpour 2K
The only two exceptions where the d orbital will first (that we know of in class up to this point) are chromium and copper. Other than those exceptions, the 4s will fill first than the 3d orbital.

Re: 3d and 4s

Posted: Tue Oct 24, 2017 11:35 am
by Tatiana Hage 2E
For chromium and copper, a completely full or half full d sub-level is more stable than a partially filled d sub-level, so an electron from the 4s orbital is excited and rises to a 3d orbital.

Re: 3d and 4s

Posted: Mon Oct 30, 2017 3:26 am
by DAllaf
Hi Mike,
Cr (Chromium) and Cu (Copper) are the two 2 exceptions that you need to know for electron configurations. Essentially what will happen is that the 3d subshell will take one of the electrons that is the 4s so that it is more stable.
Hope this helps