" Note: I've put the debate at Talk:Yttrium in the next section so that lazy editors don't
 have to click the link to see what he is talking about.

[edit] Periodic group
Surely the group 3 elements are Sc, Y , La, Ac? NOT Lu!! See, for example, long-form periodic table. Petergans (talk) 

Both conventions are common and are often a source of debate. The group 3 element article tries to explain the story. Itub (talk)  
Common? I've never seen it. Lu is a lanthanide in all the standard inorganic texts, Greenwood & Earnshaw, Cotton & Wilkinson, Housecroft & Sharpe, Shriver & Atkins ... The debate was concluded long ago. Petergans (talk)  
Just last month there was an article published in J. Chem. Ed. continuing the debate (advocating La and Ac in group 3), and it cites a few books and articles that follow the opposite convention. See [1]. There are also four letters about this topic in the same issue.[2] Itub (talk)  
Unbelievable! In 50 years as a chemist I have never, until yesterday, seen a periodic table with Lu anywhere other than in the lanthanide series. Web elements is a first for me and, as far as I'm concerned, just another example of nonsense on the web. IUPAC puts La under Y. There is no ambiguity about it, just that the lanthanide series convertionally starts with La and is usually written separately. Petergans (talk)  
This is not nonsense on the Web. There have been many textbooks published since the 1980s that put Lu under Y (I can't say whether they are the majority or the most influential). Just one example: Wulfsberg's Inorganic Chemistry. Wulfberg explains his reasoning in a footnote. In this letter to JCE, the authors looked at 35 textbooks for what they call ""flyleaf periodic tables"". If you look at the figure in the letter, among the textbooks published since 1984, 7 put La under Y, 7 put Lu, and 2 put all 15 lanthanides like IUPAC. IUPAC's table is ambiguous. It doesn't put any specific element under Y; it puts all the lanthanides there! Itub (talk)  
I'm flabbergasted. I thought elements were put in the same group because they have the same electronic configuration. The trivalent ions of Sc, Y, La, Ac have a noble gas electronic configuration. Lu(III) does not. How can it be put in the same group? (Don't answer that). I stand by the word nonsense!Petergans (talk)  
I'll dare to answer despite your request. I'm relatively neutral on this issue because I think it is largely an arbitrary convention, but I enjoy playing devil's advocate. 1) the periodic table predates knowledge of electronic configurations, and sometimes exceptions are made in the name of chemical properties (or even in the name of layout, in my opinion), such as putting helium above neon instead of above beryllium (although some tables do put He above Be!) 2) the relationship between the electronic configurations of Y and La is essentially the same as the one between Al and Ga: Al and Ga are both s2p1, but Ga has a full d shell that Al doesn't have; Y and Lu are both s2d1, but Lu has a full f shell that Y doesn't have. Trivalent Lu also has a noble gas configuration, in the sense of having no s and p electron in the valence shell, same as trivalent gallium. 3) if one looks at the neutral atom, La has the same configuration as Y, but that's an anomaly in that it doesn't follow the aufbau rule. But we don't move elements such as copper and palladium to another group just because they happen to deviate from aufbau. Finally, one slight disadvantage of putting La under Y is that you end up with a discontinuous d block in the long form of the periodic table, which looks a bit odd in my opinion. Itub (talk)  
(no indent) The counter to that argument is that, in the spirit of Mendeleev, elements a grouped together because of similarities in chemistry. Therefore it is the electronic configuration in the ""group oxidation state"" that counts, not the configuration of the atoms. Cu is the classic example [Ar]4s13d10 in the atom, but in Cu(I) the relative energies of 4s and 3d are reversed and it is the s electron which is lost on oxidation of the metal, so Cu sits comfortably in a group with Ag and Au. For Au, the f electrons are discounted as they belong to the filled 4-shell comprising 4s, 4p, 4d and 4f.

We can argue this one for ever, but what concerns me now is that the basic image of the long-form periodic table, which is used in WP for all the elements, puts Sc and Y above Lu and presents La and Ac as a group on their own. I believe that this is misleading as it does not clearly distinguish the lanthanide and actinide series from the main-group elements and transition metals. long-form periodic