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In searching online, I've noticed there are a lot of different ways to group the elements of the periodic table.

Take mercury in the two tables linked below, for example:

On the first table, it's explicitly outside of the transition metals. On the second table, it's included in the "transition metals" group.

Mercury is an example of this inconsistent classification, but in general, why is there no canonical grouping for all elements, across the periodic table? I see some tables mentioning "metalloids," but others not doing so. Or, sometimes elements are classified in entirely different groups altogether (like zinc, cadmium and mercury in the above-linked tables). Or, the lanthanides and actinides being included sometimes in the transition metals group, and sometimes not.

So which classification is right? Or rather, which one is the "most right"? Really: which one should I focus my efforts on remembering?

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closed as unclear what you're asking by Klaus-Dieter Warzecha, jerepierre, ron, Geoff Hutchison, Jannis Andreska Jun 29 '15 at 18:59

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ There, removed it. As a reference for those who can reach it: sciencenotes.org/wp-content/uploads/2014/11/… $\endgroup$ – aspyct Jun 29 '15 at 13:57
  • $\begingroup$ I would choose the more recent one. Besides ... what's wrong with the one from Wikipedia? $\endgroup$ – pH13 - Yet another Philipp Jun 29 '15 at 14:01
  • $\begingroup$ or webelements.com $\endgroup$ – user15489 Jun 29 '15 at 14:05
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    $\begingroup$ Can you make your question more specific, in particular as to the elements you're interested in? 'Alkali metals', for example, are pretty unambiguous in my mind. I agree that classification of elements like $\ce{Hg}$ is somewhat more challenging -- perhaps you should focus your question there, if that's what you're most interested in? Don't hesitate to post multiple questions, one for each grouping you want to learn more about. $\endgroup$ – hBy2Py Jun 29 '15 at 14:09
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    $\begingroup$ There is none because there is no single, 'universal' set of criteria that effectively, unarguably, and neatly divides the entire periodic table into groups. Depending on the properties of interest, different classifications/groupings are more or less appropriate. $\endgroup$ – hBy2Py Jun 29 '15 at 15:15
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There is no "most right classification scheme" for the elements of the periodic table, worth memorizing above all others. This is because there is no single, 'universal' set of criteria that effectively, unarguably, and neatly divides the entire periodic table into groups. Depending on the properties of interest, different classifications/groupings are more or less appropriate.

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  • $\begingroup$ As question is closed, I'll comment here: The specific reasons that Zn,Cd and Hg are usually not considered posttransition elements are: 1: they don't have partially filled p shells; 2: they're without doubt metals. On the other hand, they differ from other transition elements because they have full d shells. and therefore have different properties to typical transition elements. For example, Zn has only 1 common oxidation state (+2 corresponding to loss of its two s electrons) and generally forms colourless compounds (full d shell means there are no energy transitions in the visible reason) $\endgroup$ – Level River St Jun 30 '15 at 7:56

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