Atomic properties of elements determine their chemical behavior, their ionization properties and their interaction with radiation in the solar atmosphere. Whereas the chemical properties influence the condensation process in the primordial solar nebula and, hence, meteoritic abundances, ionization properties seem to provide the most important ordering parameters for producing coronal -, solar wind -, and solar energetic particle abundances from the solar reservoir. Finally, since atomic

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... es also shape the interaction of solar matter with radiation, understanding these properties determines largely the experimental reliability of photospheric chemical abundances. Isotopic abundances must be derived from nuclear properties, which are almost insensitive to atomic processes. The solar spectrum is the result of atomic processes in the solar atmosphere. The derivation of isotopic abundances from the solar spectrum is impossible for most species, conversely, the insensitivity to chemical processes makes isotopes the first choice to trace the nucleosynthetic history and the degree of mixing of galactic matter from different astrophysical sources prior to formation of the solar system. The solar wind provides a representative sample of solar isotopes and -to some degree -also a rather trustworthy representation of elements with similar atomic properties, especially volatiles, which are difficult to derive from meteoritic abundances and from optical observations of the solar spectrum.