# Why is lutetium part of the lanthanide series?

I’ve been looking at the periodic table and began to wonder - why is lutetium part of the lanthanide series? Or, for that matter, why is lawrencium part of the actinide series?

This isn’t readily apparent when looking at the traditional periodic table because the lanthanides and actinides are separate and below the main table. However, on the extended table, the two elements don’t appear that they should be in the groups that they are in: lutetium contains the $5d$ electron shell whereas the lanthanides do not, and lawrencium contains the $6d$ electron shell whereas the actinides do not.

• Lawrencium actually has an electron configuration of $\mathrm{[Rn] (7s^2) (5f^{14}) (7p^1)}$. There are multiple anomalies in the electron configurations of heavy elements and it is not simple to classify them into groups by their electron configuration. In fact it is not always simple to put them into groups at all! – bon Sep 13 '15 at 18:34
• @bon So the boundaries for the groups are actually fuzzy and not strict as taught? Or I could ignore them entirely? – Status Sep 13 '15 at 19:14
• For heavy elements, and particularly transition/rare earth metals, there is much less similarity between the reactions of elements in the same column of the periodic table. It's not like the halogens, or alkali metals, which basically all have the same reactions. – bon Sep 13 '15 at 19:55
• This video might interest you. – Martin - マーチン Sep 14 '15 at 17:52
• It's not just heavy elements having "anomalous" electron configurations. This article suggests that we are getting to a point where the whole electron shell theory breaks down. The Periodic Table, like the atomic structure on which it's based, dissolves into a fog. – Oscar Lanzi Apr 29 '18 at 20:55