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3
Li
11
Na
19
K
37
Rb
55
Cs
87
Fr
119
Uue
173
Ust

The alkali metals are a group in the periodic table consisting of the chemical elements lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). This group's electron configuration is a single electron outside a closed (noble gas) core; [NG] ns1. While not quite free, that lone electron is highly mobile. This gives the alkali metals their characteristic high electrical and thermal conductivities, as well as their high reactivity and characteristic +1 oxidation state in compounds. Alkali metals have the lowest electronegativity of all the elements of the periodic table. The alkali metals provide the best example of group trends in properties in the periodic table, with elements exhibiting well-characterized homologous behavior.

The most common alkali metal, sodium, is 14th in solar system abundance (atomic fraction) at around 2 parts per million (ppm). It is the sixth most abundant element in the earth's crust, at over 20000 ppm (molar). Reactivity of the alkali metals is high enough for them to strip oxygen from less active metals, which means they are concentrated in light compounds and complexes (minerals) and so end up at the planet's surface in high concentration.

Period 8 starts with Uue. That element is predicted to be an alkali metal, but one with a difference. Due to the small energy differences between different orbitals at high principal quantum number n, there is a chance that, in a strongly oxidizing environment, Uue will take the +3 oxidation state by losing a pair of 7 p3/2 electrons, something which cannot happen in smaller alkali metals.

There are predictions that, after Uue, the next alkali metal will be Ust (Z = 173). That's right about where our tools for describing atoms fail. Qualitatively, Ust, Bbs, etc probably have the lone electron characteristic of alkali metals - but there are no tools for supporting that belief with theory or quantifying the behavior of such atoms.

(07-20-21)

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