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Many periodic tables place lanthanum and actinium in the f-block of elements, for example, this periodic table from Los Alamos National Laboratory.

However, this table from the Royal Society of Chemsitry places lanthanum and actinium in the d-block.

Which is the most appropriate placement of these two elements on the periodic table? What is the most recent scientific consensus regarding this matter?

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  • $\begingroup$ It's really better if you reword this. I think I get what you mean, but atoms aren't in subshells. $\endgroup$ – M.A.R. Jul 5 '15 at 10:20
  • $\begingroup$ I understand this question now, there is a bit of contention about where La and Ac actually should be placed - I recall reading an article recently, I will see if I can find it. $\endgroup$ – user15489 Jul 5 '15 at 11:34
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    $\begingroup$ I edited your question to make it more clearly about what I think you mean - the placement of these two elements in the periodic table. If it is about their electron configurations, I think there is less of a debate. $\endgroup$ – Ben Norris Jul 5 '15 at 11:37
  • $\begingroup$ lavelle.chem.ucla.edu/wp-content/supporting-files/Publications/… $\endgroup$ – user15489 Jul 5 '15 at 12:42
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Lanthanum and Actinium are generally both accepted as f-block elements. You will notice in the Royal Society's periodic table, La and Ac are both color coded to match the other f-block elements. They do this to show the beginning of both the Lanthanide and Actinide series, while maintaining a reasonable symmetry for their periodic table (that is, without "holes" in their table, similar to the first link you provided).

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  • $\begingroup$ Then what are your counter-arguments against this? $\endgroup$ – M.A.R. Jul 5 '15 at 16:04
  • $\begingroup$ I suppose I was conforming to the more generally accepted placement of La and Ac (Lavelle's "general chemistry books"). Realize the topic of his paper is to suggest why both La and Ac should be considered f-block and not d-block elements, the latter of which is the general view--my view. Albeit my argument is less technical, I support the general acceptance of Ac and La being members of the f-block; and view/explain the differences in the above periodic tables with my generally accepted view. $\endgroup$ – fruitegg Jul 5 '15 at 16:17
  • $\begingroup$ Correction: Lavelle argues La and Ac should be d-block, not f-block. $\endgroup$ – fruitegg Jul 5 '15 at 21:21
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Lanthanum and actinium are usually regarded as d-block elements (Myers, Oldham & Tocci 2004, p. 130) and generally counted as lanthanides and actinides (the rest of which occupy the f-block). Some periodic tables, like the one from LANL emphasise chemical similarities, so lanthanum and actinium are shown at the foot of the table, along with the f-block elements. That's fine, but leaves a hole under yttrium so it isn't clear which two elements go there. Other tables, like the one from the Royal Society of Chemistry, presumably rely on electron configurations to work our which elements fit under yttrium, and use colour shading to emphasise similarities in chemical behaviour.

Myers RT, Oldham KB & Tocci S 2004, Holt Chemistry, Holt, Rinehart and Winston, Orlando

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