The Periodic Table of the Elements: Historical Origins and

of Chemical Elements

Early in nineteenth century it was discovered that there are groups (triplets) of chemical elements with similar chemical properties among which the molar masses increase rather regularly:

– phosphorus, arsenic and antimony (roughly 31, 75 and 122), – lithium, sodium and kalium (7, 23, and 39),

– beryllium, magnesium, and calcium (9, 24, and 40) or – calcium, strontium, and barium (about 40, 87, and 138),

meaning the “middle” value is close to the arithmetic mean of the other two (Doebereiner’s triads, Fig.2.15).

Now we know that there are electrons orbiting and “wrapping” a nucleus (which latter was unknown to exist till 1911), electrons which can be bound weaker or much stronger to the latter. Weak bonding causes cations to form easily (metals) while strong binding of also additional electrons translates into ready formation of both covalent bonds and anions (non-metals). Doebereiner’s rule of triads (Do¨bereiner 1819) thus lets us to assume that

– there are similar effects in both electron shells and nucleus (being constructed of similar shells of both protons and neutrons) causing utmost stability, and that

Fig. 2.15 Doebereiner’s triads (Do¨bereiner 1819) as corresponding to modern PSE representations

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– similar electron configurations and binding properties repeat regularly among the chemical elements (here,ΔZ ¼ 8 or Δ’Z ¼ 18, respectively).

Dimitry I Mendeleyev and Lothar Meier (in the late 1860s) extended Doebereiner’s finding to many more elements, thus constructing the periodical system of elements independent of each other. Yet the periodical system of ele-ments had to be accommodated once again (Seaborg in late 1940s): With discovery in nature, the continuous fractionation of rare earth oxides (achieved 1843–1907) followed by preparation by nuclear reactions two more large groups of elements had to be “accommodated” to the PSE. Thus the subgroups of lanthanoids (Z¼ 58 [Ce]–71 [Lu]) and actinoids⁷[Z¼ 90 [Th]–103 [Lr]) were inserted into the periodic system. Ongoing synthetic efforts (Z> 103 up to 118, i.e. Rf, Db, Sg. . .) were added by superheavy representatives of the common transition-, platinum group-, coinage- and main group elements [Z> 112 up to 120] so, that now the system is almost complete⁸(Fig.2.16).

Fig. 2.16 The present state of the PSE (2014) includes superheavy Platinum Group Metals (PGMs: Hs, Mt, Ds), coinage metals (Rg), carbon-group (eka-lead flerovium Fl) member and chalcogenes (dwi-tellurium livermorium Lv) although even few-atom chemistry experiments until now are limited to Z< 109

7While for the actinoids similarity with lanthanoids was driven so far as to name analogs according to similar rules (Z¼ 63: europium, Z ¼ 95: americium; Z ¼ 65: terbium (alluding to a village in Sweden where it was found first), Z¼ 97: berkelium) the lighter actinoids (protactinium to americium) differ from their REE analogs in stabilizing oxidation states + V to + VII which the latter will never reach in condensed matter while the heavy ones (Z> 100, Md [mendelevium], No, and Lr) turned out to be commonly much more stable in divalent states than corresponding REEs Tm, Yb, let alone Lu.

8To our present knowledge it will be almost impossible to prepare atoms with Z> 123 of sufficient half-lives (>0.2 μs) even to identify them (otherwise, nuclei formed in a target would decay during mass separation and hence before reaching the detector device), let alone doing any chemistry.

The present (2014) “record” of making very large atomic nuclei is Z¼ 118 (²⁹⁴118), a still-unnamed noble gas (working name “moscovium”), whilst the heaviest element which already was given an official name by IUPAC is the chalcogene (homolog of Te and Pb) livermorium (Lv, Z¼ 116). Except for neutron stars and their gravitational disruption by close access before mergers, there are no hints that nature does any better; on the contrary, it is unlikely every of the processes of stellar nucleosynthesis would produce anything with Z> 101.

Generally speaking, the PSE organizes the manifold of chemical elements according to periodicities brought about by the number of electrons orbiting some atomic nucleus vs. the aufbau principle. It is related to Pauli’s law and electrons having half-integer spin, which means not even two of them can occupy the same site or state within some connected structure. The organization of atom structures can be accounted for by Pauli’s principle mainly, and oxidation states, stability and even physical properties of certain compounds can be predicted by this reasoning (which already Mendeleyev did much before any knowledge of electrons, atomic nuclei, let alone quantum mechanics). Small (about 1/1,800 of a proton or neutron) mass, half-integer spin, and mutual electrical repulsion of electrons unbalanced by anything else than spin-pairing⁹cause electrons to produce fairly extended assem-blies. They follow hierarchical rules which were found long before one got the theoretical means to understand their reasons.

By the way, if the electron spin value was different, there was no way either to distribute electrons across a network of positively charged nuclei arranged some-how in space; in fact, rather than forming any molecules electrons would accom-modate very close to one of the nuclei (that is, the more positively charged one). So there could be salts¹⁰ in such a world but no molecules other than homoatomic diatomic ones, of course excluding formation of any polymers required to construct living beings. Moreover, the lightest elements, particularly hydrogen, would any-way give aany-way their electrons to any heavier ones: H₂could exist but there would be only very strong acids instead of any compounds with covalent element-hydrogen bonds other than H₂. The redox behavior would be right the other way round than it actually is: antimony, tellurium, iodine (and xenon, caesium, barium!) attracting electrons much more strongly than nitrogen, oxygen or fluorine, do!

Accordingly, there would be only metal ions with Ahrland B-type behavior.

9On the opposite, protons and neutrons in nuclei attract both each and the other kind of nucleon due to the strong nuclear force, partially compensating mutual repulsion of protons even though they are tightly packed. Thus the “magic” numbers producing closed, most stable nuclear orbitals (8, 20, 28, 50, 82, 126, plus 14, 34, 62, 108 for non-spherical arrangements) differ from the Z values of noble gases (10, 18, 36, 54, 86, and 118) and fairly inert metal ions (28, 46, 78) which are caused by electron properties alone.

10Both one-dimensional ones, ylides, and three-dimensional assemblies of charged atoms.

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