Cesium auride

Band structure cesium auride, 25 240-241 graphite-alkali metal compounds, 23 287 Band theory, for one-dimensional electrical Conductors, 26 237-241 Barbituric acid, 18 187 Barium... 

Although the increased electron affinity associated with the heavier elements usually manifests itself only indirectly (via electronegativity, etc.), it is directly responsible for the fact that cesium auride, Cs Au, is an ionic salt rather than an alloy. Both the increased ionization energy and increased electron affinity in these elements result from relativistic effects. 

CsAu Cesium auride NH4CI — Ammonium chloride... 

Elements are named in the same order as they appear in the formula (see above). Although there is no implication that the compound is ionic, the names ending in -ide are the same as those used for anions (e.g. fluoride, F ). For the elements listed in Table 1. anion names are derived not from English but from the Latin name which gives the chemical symbol. For example, CsAu is cesium auride. 

As a result of relativistic orbital contraction, the atomic radius of Au is less than that expected on the basis of its periodic trends Cu (135 pm), Ag (160 pm), and Au (135 pm). Because of the small size of its half-filled 6s orbital, the E.A. of Au (223kJ/mol) is considerably larger than that for Ag (l26kJ/mol) orCu (I l8kJ/mol). In fact, the E.A. of Au is so large that gold exists as the Au anion in the compound cesium auride (CsAu). 

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