Caesium, electronegativity

This description would assign to the caesium atom in the caesium fluoride crystal a resultant charge + and to the fluorine atom a charge — It has seemed to me likely that in general all of the atoms in the complexes that constitute stable chemical substances have resultant electrical charges smaller than those shown by these most electropositive and electronegative atoms in their compounds with one another, and I have accordingly formulated the postulate of the essential electrical neutrality of atoms namely, that the electronic structure of substances is... 

Different metal chlorides unite with one another to form double lasts. Just as the acidic and basic oxides unite together to form oxy-salts, so do the halides of an electropositive element (or radicle) unite with a halide of a less positive element (heavy metal or metalloid) to form double halides. So far as is known the alkali chlorides do not unite with one another to form double salts, nor do the halides of the same natural group form compounds with one another, but compounds of the alkali chlorides with the chlorides of the more electronegative chlorides are known. A comparison of nearly 500 double halides has been made by H. L. Wells (1901).1 He calls the one component—e.g. the alkali halide—the positive halide, and the other the negative halide. A. Werner calls the halide which plays the role of the basic oxide, the basic halide, and the other, the acid halide. A great many of the simple types of the double salts predominate. Writing the number of molecules of the positive halide first, and the negative halide second, salts of the 2 1 and 1 1 ratios cover about 70 per cent, of the list of known double halides, and 4 1, 3 1, 3 2, 2 3, and 1 2 represent over 25 per cent. Two halides sometimes unite in several proportions—for instance, six caesium mercuric halides have been reported where... 

An electropositive metal in organic compounds of alkali metals is replaced by a more electropositive one in series of reversible reactions. More electronegative, i. e. more acid, hydrocarbon groups or whole molecules replace those which are less acid [140]. Caesium replaces lithium in ethyllithium. Benzene, which is a stronger acid than ethane, replaces ethyl in ethyllithium. Toluene and H2 are more acid than benzene, and they can therefore replace phenyl in phenylsodium [141, 142],... 

NaK the bond may be regarded as covalent, but in molecules formed from atoms of widely differing electronegativity, e.g, LiCl, NaCl, NaBr, KI, the bond is almost entirely ionic. Caesium fluoride presents a special case however, since the electron affinity of fluorine (95 kcals) is greater than the ionization potential of caesium (89 kcals) so that in the change of caesium and fluorine atoms into ions, a small liberation of energy, amounting to 6 kcals, occurs. 

We have already considered in detail the structures of the alkali halides, all of which crystallize with either the sodium chloride or the caesium chloride arrangement ( 3.04 and 3.05). All of these compounds are essentially ionic, and the degree of ionic character depends on the difference in electronegativity of the atoms concerned it is thus a maximum in caesium fluoride and a minimum in lithium iodide. As we have seen, the radius ratio r+jr is the primary factor in determining whether a given halide possesses the sodium chloride or the caesium... 

This behaviour is explained by low first ionization energy, low electronegativity and low electron affinity and large atomic radius. Reactive metals form very basic oxides. So caesium oxide is expected to react with water to form caesium hydroxide, which is expected to be fully soluble and completely ionized in water. 

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