1. The problem statement, all variables and given/known data If ionization energy is 899.4 kJ/mol for Be, what is the effective nuclear charge? 2. Relevant equations Zeff = Z - S E=RH(Z2/n2) ?? E=RH(Zeff2/n2)?? 3. The attempt at a solution My attempted solution was subbing into Zeff = Z - S Zeff = 4 - 2 = 2 But I suspect that is wrong... because why ionization energy is given.. so shouldn't it be used in the calculation? And somewhere I think I read that "S" was supposed to be a "constant" of some sort, and I just subbed 2 in because I thought that it was the number of electrons in the first orbital ?