![]() ![]() The same is true for the covalent part of the bond energy, which is also greater in LiF than in CsF. The problem is in the form of formula ( 1): Li–F bond length is much shorter than Cs–F and ionic term should of course be stronger in the shorter bond in Li F − than in Cs F −. The values one finds from ( 1) and experimental bond dissociation energies are X(Li) = 1.85, X(Na) = 1.96, X(K) = 1.99, X(Rb) = 2.00, X(Cs) = 1.93 these are very different from standard Pauling’s electronegativities of 0.98, 0.93, 0.82., 0.82, and 0.79, respectively (see Supplementary Fig. Strangely, Pauling’s electronegativities of alkali metals (and, equally badly, alkali earth metals) cannot be obtained from their highly ionic molecules using Pauling’s formula ( 1). ![]() According to ( 1) this should indicate that Li is the most electropositive alkali metal and overall electronegativity increases down the group of the periodic table-which is exactly contrary to chemical intuition and to the values one finds in Pauling’s scale. Where D AB is the dissociation energy of a single chemical bond between two different atoms A and B, \(D_^2\), so we start with alkali and alkali earth fluorides. ![]()
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