Self-consistent, non-relativistic Hartree-Fock calculations on a finite cluster of atoms with zinc at the center have been performed on the zinc blende compounds ZnTe, ZnSe, ZnS, on ZnO (wurtzite structure), ZnO (NaCl structure), and on ZnF2 (rutile-type structure) to obtain changes in s electron density Δρ(0) at the67Zn nucleus. We solved the eigenvalue problem of the dynamic matrix to calculate the second-order Doppler shiftSSOD using appropriate force constant models and determined the isomer shiftS from the measured center shift for each compound. Our calculations clearly show the importance of the covalency of the Zn-ligand bond for the origin ofS and fully corroborate the experimental linear correlations between decreasingS values and increasing electronegativity of the ligands. The most important contribution to Δρ(0) comes from the Zn(4s) electrons, with a smaller but significant contribution from the Zn(3s) electrons. For the change of the mean-square nuclear charge radius for the Mossbauer transition in67Zn, we obtain Δ〈r2〉=+(13.9±1.4) × 10−3 fm2.