Core electrons strength

Hardness or softness is a property of a Lewis acid or base that is independent of its strength. An important aspect of electron availability is polarizability, the ease of distortion of the valence electron shell of an atom by an adjacent charge. For example, the valence electrons of iodide are shielded from the nuclear charge by all of the core electrons and thus are capable of being distorted toward a partially positive reactive site much more easily than the valence electrons of fluoride. Polarizability increases going down a column in the periodic table. For our purposes, it is more important to be able to compare the relative hardness of acids and bases several trends are helpful. 

With high-resolution techniques the rather weak influence of valence electrons on the binding strength of core electrons is detectable. This essential feature of XPS is demonstrated in Figure 6.4, where spectra of polyethylene (P ), poly (ethylene terephthalate) (PET) and poly(vinylidene fluoride) (PVDF) are shown. While the spectrum of PE contains only a single peak at 285.0eV, assigned to aliphatic carbon (C—C, C—H), the spectrum of PET exhibits three peaks assigned to aromatic carbon (C rom) at 285 eV, C—O-bonded carbon at 286.6 eV, and carboxylic carbon (O—C=0) at 289.9 eV. The Cig spectrum of PVDF shows two carbon lines at 285. OeV (aliphatic carbon) and 290.0 eV (CF2 carbon) in the stoichiometric ratio. 

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