| MadSci Network: Chemistry |
The electron configurations that are given for the various transition elements and rare earth elements are very complicated. The one that is quoted is for the ground state (lowest energy), and often some of the other configurations come in just a very small energy gap higher. If you are asking this question, you probably know about Chromium and Copper and the irregularities associated with the shell filling in these elements: Ti -- [Ar] 3d2 4s2 Co -- [Ar] 3d7 4s2 V -- [Ar] 3d3 4s2 Ni -- [Ar] 3d8 4s2 Cr -- [Ar] 3d5 4s1 Cu -- [Ar] 3d10 4s1 Mn -- [Ar} 3d5 4s2 Zn -- [Ar] 3d10 4s2 What happens in fact is that there is a 3d4 4s2 configuration for chromium, but the lowest energy state corresponding to that configuration comes in just a little higher in energy than the lowest energy d5 s1 state. Similar irregularities happen in the lanthanide (rare earth) series: La -- [Xe] 5d1 6s2 Ce -- [Xe] 4f1 5d1 6s2 Pr -- [Xe] 4f3 6s2 Nd -- [Xe] 4f4 6s2 Pm -- [Xe] 4f5 6s2 Sm -- [Xe] 4f6 6s2 Eu -- [Xe] 4f7 6s2 Gd -- [Xe] 4f7 5d1 6s2 Tb -- [Xe] 4f9 6s2 ..... Tm -- [Xe] 4f13 6s2 Yb -- [Xe] 4f14 6s2 Lu -- [Xe] 4f14 5d1 6s2 (Authority: Greenwood & Earnshaw,'Chemistry of the Elements', Pergamon 1989, p. 1430.) There are very complicated spectroscopic reasons for these irregularities. They have almost no effect on the chemical properties of the various elements.
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