Alternative Periodic Tables

In practice, the period 6 and 7 elements have quite a few violations of the Afbau principle, and some predictions of period 8 predict some truly anomalous things for electron configuration (e.g., let's start filling up the 9s/p shells before the 8p shell is finished).

Those four elements are yttrium, erbium, terbium, and ytterbium. The short answer as to how a small village could get so many elements named after it is that rare earth elements are so difficult to separate from each other. So the compound that was thought to be yttrium was actually a mixture of several of them. (Cerium provided the other group of rare earths--this eventually resulted in didymium, which was considered an element for a few decades until people realized it was actually a mixture of praseodymium and neodymium). Terbium and erbium were the second and third elements found from yttrium.

The obvious one is that He (which is only a full s shell) is far more similar to elements with full p shells than those with only a full s shell. In terms of bonding, the outermost s and p shell influences bonding the most. He, who has no p shell, acts far more like an element that has a full p shell than an element that only has a full s shell and an empty p shell because of the influence of the p shell on bonding, so you do want to stick He in the same group as Ne, Ar, Kr, Xe, and Rn.

The other thing that is tricky is where the f block starts to integrate in the table. The f shell of electrons is far less involved in bonding and observable effects than the d shell is. Furthermore, even the basic electron configuration breaks down because the f and d blocks are so similar in energy. La and Ac both fill their first d electron before the f electron, and several actinides actually retain this single outermost d electron rather than dumping everything in the f block. There is some dispute as to whether or not you should put La/Ac in the d block, or Lu/Lr in the d block, or instead put the entire La-Lu/Ac-Lr block in that one-element hole (this is perhaps one of the reasons why people like using the short form a lot--you can be somewhat vague here).