Question 40

[antwan_hog1489]

PS GS-6 #40

Which of the following electronic configurations is an accurate representation of the electron distribution in a chromium atom?

1. 1s2, 2s2, 2p6, 3s2, 3p6, 3d6 , 4s0 [x]
2. 1s2, 2s2, 2p6, 3s2, 3p6, 3d5 , 4s1 [x]
3. 1s2, 2s2, 2p6, 3s2, 3p6, 3d4 , 4s2 [x]
4. 1s2, 2s2, 2p6, 3s2, 3p6, 3d3 , 4s2, 4p1

Answer is #2

The answer explanation states:
"a half-filled 3d orbital creates a more stable atom."

Can someone explain why? Also, when does one know to use this concept?

[admin]

Half-filled (ie. Cr) and filled (ie. Cu, Ag, Au) d orbitals have remarkable stability. This stability makes for unusual configurations. Thus by the rules Cr = 4s2 3d4 but in reality Cr = 4s1 3d5 creating a half-filled d orbital. Some metal ions form colored solutions due to the transition energies of the d-electrons. That is the extent of understanding that you require for the new MCAT.

[dnpgr16513]

So in what instance do we state the NORMAL electronic configuration? Like when we DON'T try to make it more stable? Or is this never the case? I thoughT that when it wants us to list the configuration of an ATOM we state it how the atom is: no alterations..

THANKS!!!!!!!!!!!!!!

[larubio25277]

You mainly use this only with transition metals. Say if the transition metal has a chance to either have a half or full d orbital (they have either 4 or 9 originally) it will take an electron from the previous s orbital to achieve a half full (5) or full (10) d orbital. Just be wary of the position of the transition metals on the periodic table so that you may know when to take the electron from the s orbital and move it to the d orbital and form the more stable transition metal. I hope this helps.

[mohsinalam5969]

Chromium has an electron configurations [Ar] 3d5 4s1 and i.e. one electron has passed from the 4s-orbital to a 3d-orbital to generate a half-filled or filled subshell. In this case, the usual explanation is that "half-filled or completely filled subshells are particularly stable arrangements of electrons".
As there is more stability of the element if it is like 3d5 4s1 as 5 orbitals of d subshell and 1 orbital of s subshell are singly filled means there is one electron in each orbital and it is stable. But if it would have like 3d4 4s2 then there would be 4 orbitls of d subshell filled and one would be empty and not much stable, so one electron from 4s jumps to 3d to fill that empty orbital and make it more stable. So its full configuration is 1s2 2s2 2p6 3s2 3p6 4s1 3d5.This mainly happens in case of transition metals.