BR Question: The ionization energy of H (g) is 1312 kJ/mole. A good approximation for the second ionization potential of helium (g) is: ANSWER: 5248 kJ/mole What I dont understand is part of the explanation. It states how the Zeff value of H is +1 and the Zeff value of helium is +2. I thought that in order to find Zeff then the equation would be protons- core electrons (2). Why is this equation not used in the problem to find the Zeff? Thank you!