Editing Alkali metal (section)

=== Coordination complexes ===
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| image1 = 18-crown-6-potassium-3D-balls-A.png
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| caption1 = [[18-crown-6]] coordinating a potassium ion
| image2 = Cryptate of potassium cation.jpg
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| caption2 = Structure of [[2.2.2-Cryptand]] encapsulating a potassium cation (purple). At crystalline state, obtained with an X-ray diffraction.<ref>{{cite journal |last1=Alberto|first1=R. |last2=Ortner|first2=K. |last3=Wheatley|first3=N. |last4=Schibli|first4=R. |last5=Schubiger|first5=A. P. |title= Synthesis and properties of boranocarbonate: a convenient in situ CO source for the aqueous preparation of [<sup>99m</sup>Tc(OH<sub>2</sub>)<sub>3</sub>(CO)<sub>3</sub>]<sup>+</sup> |journal= [[J. Am. Chem. Soc.]] |year= 2001 |volume= 121 |pages= 3135–3136 |doi= 10.1021/ja003932b |pmid=11457025 |issue= 13|bibcode=2001JAChS.123.3135A }}</ref>
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Alkali metal cations do not usually form [[coordination complex]]es with simple [[Lewis base]]s due to their low charge of just +1 and their relatively large size; thus the Li<sup>+</sup> ion forms most complexes and the heavier alkali metal ions form less and less (though exceptions occur for weak complexes).<ref name="Greenwood&Earnshaw" />{{rp|90}} Lithium in particular has a very rich coordination chemistry in which it exhibits [[coordination number]]s from 1 to 12, although octahedral hexacoordination is its preferred mode.<ref name="Greenwood&Earnshaw" />{{rp|90–1}} In [[aqueous solution]], the alkali metal ions exist as octahedral hexahydrate complexes [M(H<sub>2</sub>O)<sub>6</sub>]<sup>+</sup>, with the exception of the lithium ion, which due to its small size forms tetrahedral tetrahydrate complexes [Li(H<sub>2</sub>O)<sub>4</sub>]<sup>+</sup>; the alkali metals form these complexes because their ions are attracted by electrostatic forces of attraction to the polar water molecules. Because of this, [[anhydrous]] salts containing alkali metal cations are often used as [[desiccant]]s.<ref name=generalchemistry /> Alkali metals also readily form complexes with [[crown ether]]s (e.g. [[12-crown-4]] for Li<sup>+</sup>, [[15-crown-5]] for Na<sup>+</sup>, [[18-crown-6]] for K<sup>+</sup>, and [[21-crown-7]] for Rb<sup>+</sup>) and [[cryptand]]s due to electrostatic attraction.<ref name=generalchemistry />