What is effective nuclear charge of S2 - and S? Does the Z eff differs from ions and atoms of the same element

When they say we need an effective nuclear charge we are asked to estimate the charge experienced by the electrons called valence. So we need to know how many Valence electrons does sulfur and apply the Slater's rule. The effective nuclear charge would be + 5.5. Now for the second question we have to say that the Z eff does not differ from ions and atoms of the same element