Wikipedia:Reference desk/Archives/Science/2016 July 16

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July 16

Ionisation energies of actinides and lanthanides

I would have expected that the actinides would have lower ionisation energies than the lanthanides, since the 5f electrons would be further away from the nucleus than the 4f electrons of the lanthanides, and wouold be screened by more electrons. Furthermore, since only the first two lanthanides (Ce and Pr) can reach the oxidation state corresponding to the loss of all valence electrons (and Pr needs noble-gas matrix isolation conditions to do so), but the first five actinides can do it (Th, Pa, U, Np, and Pu, although only transiently for Pu), it would seem that the outer electrons of the early actinides are being held less firmly than those of the early lanthanides. Yet the list molar ionization energies of the elements on Wikipedia gives the opposite trend: Th has first ionisation energy 587 kJ/mol, while Ce has 534.4 kJ/mol, for example. Why is this so? Double sharp (talk) 14:16, 16 July 2016 (UTC)

In general, actinide behavior does not obey the periodic law as well as lower atomic number elements. That is, the trends predictable by an elements position on the periodic table break down by the time one gets to the actinides. Part of this is connected to the unpredictability of the electron configuration of actinides. Thorium for example has [Rn] 6d2 7s2 while Protactinium is [Rn] 5f2 6d1 7s2 and so on. --Jayron32 02:27, 17 July 2016 (UTC)

Could you go into a little more detail behind the causes for this? Maybe it's easier for a specific case, so for example, in particular, why is removing a 6s electron from a cerium atom easier than removing a 7s electron from a thorium atom? (And why is it that the pairs La/Ac, Gd/Cm, and Lu/Lr are exceptions, and behave the way I would naïvely think they ought to, with lanthanum having a higher ionisation energy than actinium?) Double sharp (talk) 12:17, 18 July 2016 (UTC)

Not in the sense of "here's an alternative model that WOULD predict the behavior of f-block elements more accurately". The problem is a problem with mathematical modeling of complex systems more generally. It's a related issue to what is known in physics as the n-body problem. Strictly speaking, predicting the long-term behavior of ANY bound system consisting of more than 2 bound particles is impossible. That's what lead to the abandonment of the bohr model as a predictive tool for the more robust quantum mechanical model; the Bohr model (and its mathematical expression the Rydberg equation) only quantitatively works for Hydrogen-like atoms, meaning it has limited utility. Just to get back to our discussion here, the issue is that the interplay between more and more electrons becomes more and more complex, so the predictive power of simple models gets overwhelmed as small variations become more complex. There's a small "glitch" in the d-block that demonstrates this; chromium and copper both have configurations that don't fit the pattern. The a posteriori explanation of this is that the slight increase in stability caused by spin-spin coupling is enough to overcome the difference between the 4s and 3d electron orbitals, meaning that overall (in the case of, say, chromium) the 4s1 3d5 configuration is favored over the predicted 4s2 3d4 configuration. Normally, the slight decrease in potential energy caused by such an effect doesn't cause a deviation from predicted patterns, but as you get MORE and MORE moving parts, such small effects become magnified. With f-block electrons, the difference in energy between 7s, 6d, and 5f becomes SO miniscule, that very tiny effects can cause deviations from expected patterns. If I had to summarize the reasoning it is that, as one gets higher in energy, the difference between orbital energies decreases; so the larger the atom, the smaller the energy difference between orbitals, and thus the more likely miniscule effects can cause deviation from expected behavior. --Jayron32 16:37, 19 July 2016 (UTC)

Adolescent

1. Define, [pre-/???], [main-/mid-], [post-/late-]adolescent age group.
2. What’s the correct word to use from “[ ]” stated above?

Apostle (talk) 18:38, 16 July 2016 (UTC)

Read Adolescence. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:29, 16 July 2016 (UTC)

"Pubescent" is often used in that context. The ages vary quite a bit, depending on sex, ethnicity, diet, and weight.StuRat (talk) 21:20, 16 July 2016 (UTC)

I Know, this is where the confusion is, I don't know whether I should use age numbers or the words specified in this post for my book. Any suggestion? -- Apostle (talk) 06:38, 17 July 2016 (UTC)

Choose whichever you prefer, define them clearly, and be consistent. Wymspen (talk) 10:58, 17 July 2016 (UTC)

Thats the problem, I have ESL issue. -- Apostle (talk) 04:58, 18 July 2016 (UTC)

What is it about the term "adolescence" that you do not understand? ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:19, 18 July 2016 (UTC)

• Our crystal balls don't tell us how you want to use such a word. —Tamfang (talk) 20:56, 17 July 2016 (UTC)

Lol. -- Apostle (talk) 04:58, 18 July 2016 (UTC)

Baseball Bugs: I want to use the word adolescence/adolescent rather than "At the age of _____,". If you can specify the age period (from to to) than I'll know the period.

So what do guys say?

Apostle (talk) 06:06, 19 July 2016 (UTC)

Using ages will be most clear, but using something like "late adolescent" might carry more of the feeling of "not quite adult yet". It does depend a bit on what you want to convey. It is true that having lots of ages and numbers in a novel is weird. Most authors don't write things like "Chang was 43 years old and weighed 196 lbs, with a height of 5'6". It would read more naturally to write "Change was middle aged, middle height, and slightly chubby". (PS if you are thinking about word choice as you seem to be here, the language desk is probably a better location, even if it touches upon scientific concepts.) SemanticMantis (talk) 16:42, 20 July 2016 (UTC)

Creation and evolution in Russia

Of the approximately 145,000,000 residents of Russia, (a) how many believe that life was created by a supernatural intelligence, and (b) how many believe that life originated by spontaneous biogenesis and developed by macroevolution? (Also, how are those statistics distributed: by age, by sex, by subnational entity, by education, by occupation, and by religious status?)—Wavelength (talk) 23:13, 16 July 2016 (UTC)

Not as detailed as what you requested, but relevant: Creationism in Russia? Shock Brigade Harvester Boris (talk) 23:40, 16 July 2016 (UTC)