The adequacy of the 2h-1p CI scheme for the interpretation of the valence ionization shake-up was first analysed in Ne and Ar, paying special attention to the choice of an adequate basis set, the explicit inclusion of relaxation by the use of relaxed orbitals and the correlation of the ground state. The scheme was then applied to the calculation of the shake-up of the isoelectronic series of hydrides: i.e. HF, H2O, NH3 and CH4; HCl, H2S, PH3 and SiH4. The results obtained compare well with experiments and previous calculations, showing that in the hydrides the shake-up is dominated by the same effects as in Ne and Ar.
