[en] The theoretical and experimental studies of the atomic and electronic structures of apatite compounds of strontium are investigated. The changes of the electronic structure of Sr₅(PO₄)₃OH (Sr-HAP) on the isomorphous substitution of anion groups OH^- by F, Cl and Sr by Na, La, as well as on the transition of Sr-GAP in the amorphous state are studied. The greater changes in the binding energy of the core electrons of Sr on the isomorphous substitution of OH by F and Cl are detected. It is shown that the binding energy of Sr 2p_3/2 electrons in Sr-GAP is similar to that of Sr 2p_3/2 in SrCO₃ for various binding energies of O 1s electrons