Editing Caesium (section)

====Halides====
[[File:CsX@DWNT.jpg|thumb|upright|Monatomic caesium halide wires grown inside double-wall [[carbon nanotube]]s ([[transmission electron microscopy|TEM image]]).<ref name="chains">{{cite journal |doi=10.1038/ncomms8943 |pmid=26228378 |pmc=4532884 |title=Single-atom electron energy loss spectroscopy of light elements |journal=Nature Communications |volume=6 |pages=7943 |year=2015 |last1=Senga |first1=Ryosuke |last2=Suenaga |first2=Kazu |bibcode=2015NatCo...6.7943S}}</ref>]]
[[Caesium fluoride]] (CsF) is a [[hygroscopic]] white solid that is widely used in [[organofluorine chemistry]] as a source of [[fluoride]] anions.<ref>{{cite journal |author=Evans, F. W. |author2=Litt, M. H. |author3=Weidler-Kubanek, A. M. |author4=Avonda, F. P. |title=Reactions Catalyzed by Potassium Fluoride. 111. The Knoevenagel Reaction |date=1968 |journal=Journal of Organic Chemistry |volume=33 |pages=1837–1839 |doi=10.1021/jo01269a028 |issue=5}}</ref> Caesium fluoride has the halite structure, which means that the Cs<sup>+</sup> and F<sup>−</sup> pack in a [[cubic closest packed]] array as do Na<sup>+</sup> and Cl<sup>−</sup> in [[sodium chloride]].<ref name="greenwood"/> Notably, caesium and fluorine have the lowest and highest [[electronegativity|electronegativities]], respectively, among all the known elements.

[[Caesium chloride]] (CsCl) crystallizes in the simple [[cubic crystal system]]. Also called the "caesium chloride structure",<ref name="HollemanAF"/> this structural motif is composed of a [[primitive cell|primitive]] cubic lattice with a two-atom basis, each with an eightfold [[coordination number|coordination]]; the chloride atoms lie upon the lattice points at the edges of the cube, while the caesium atoms lie in the holes in the centre of the cubes. This structure is shared with [[caesium bromide|CsBr]] and [[caesium iodide|CsI]], and many other compounds that do not contain Cs. In contrast, most other alkaline halides have the [[sodium chloride]] (NaCl) structure.<ref name="HollemanAF"/> The CsCl structure is preferred because Cs<sup>+</sup> has an [[ionic radius]] of 174&nbsp;[[picometer|pm]] and {{chem|Cl|−}} 181&nbsp;pm.<ref>{{cite book |last=Wells |first=A. F. |date=1984 |title=Structural Inorganic Chemistry |edition=5th |publisher=Oxford Science Publications |isbn=978-0-19-855370-0}}</ref>