![]() ![]() However, no alkali metal anion with a charge beyond −1 has been reported thus far. This feature makes these anions candidates for nonlinear optics. The alkali metal anions therefore exhibit large polarizability 13. When electrons are detached from the embedded alkali metal cations, they either fill the interstitial sites forming electrides or, if there are alkali metal atoms available, bind loosely to them. The unique oxidation states are related to another class of materials called electrides 6, 8, 9, 10, 11, 12. ![]() These unusual compounds contain alkali metal anions as well as alkali cations embedded in organic molecules such as cryptands or crown ethers 3, 4, 5, 6, 7. However, alkali metals may also exhibit an atypical charge state of −1 in a class of compounds called alkalides. The main group elements on the left side of the periodic table (group I and II) tend to lose electrons in these outermost orbitals and assume a +1 or +2 oxidation state 2. The atomic orbitals below and above (in energy) the outermost shell are usually not essential in defining the chemical properties, although these orbitals may still play a minor role. As revealed by the atomic shell structure, the outermost atomic orbital and the respective number of electrons occupying the orbital control this fundamental feature. The propensity of losing or gaining electrons is an essential trait of an element that determines its chemical reactivity and the structures and properties of the compounds formed 1, 2. ![]()
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