energy

[MIA6]

E=1/n^2 (-13.6eV) for other one-electron atoms –ionized helium (Z=2), doubly-ionized lithium (Z=3),etc. I found contradicting here is that one-electron atom and Z=2, 3. If it’s one electron, then there is only one proton, so where do 2 or 3 protons come from?
Thanks.

[cepheid]

Umm...doubly ionized Lithium is missing two of it's electrons. Hence it has one electron and three protons. That's why it is IONized.