![]() Knowing the atomization energy, the first ionization energy, and the hydration enthalpy, however, reveals useful patterns. The summation of these effects eliminates any overall pattern. The extra protons in the nucleus are again screened by the extra layers of electrons. As the ions increase in size, the water molecules are farther from the attraction of the nucleus. The hydration enthalpy is a measure of the attraction between the metal ions and lone pairs on water molecules. ![]() The extra protons in the nucleus are screened by additional layers of electrons. The first ionization energy decreases because the electron being removed is more distant from the nucleus with each progressive atom.The delocalized electrons are further from the attraction of the nuclei in the larger atoms. This decreases as the size of the atoms and the length of the metallic bond increase. The atomization energy is a measure of the strength of the metallic bond in each element.There is no overall trend in the overall reaction enthalpy, but each of the component input enthalpies (in which energy must be supplied) decreases down the group, while the hydration enthalpies increase: We can write the changes for the Cs atom as. 2Cs (s) + 2HO (l) H (g) + 2Cs (aq) + 2OH (aq) The reaction is so explosive that it often shatters the container. In each case, the aqueous metal hydroxide and hydrogen gas are produced, as shown: where X X is any Group 1 metal. All of Group 1 elements lithium, sodium, potassium, rubidium and cesium react vigorously or even explosively with cold water. These values are tabulated below (all energy values are given in kJ / mol): Element Cesium reacts with cold water to form hydrogen gas and a solution of cesium ions and hydroxide ions. Reactions of Group 1 Elements with Water.
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