I am an A-level teacher so I don't want an answer in terms of anything too complicated (for my students!) The hydrogen atom has a ground state energy of -13.6eV. I am happy with this. This means that the electron needs 13.6eV of kinetic energy in order to become free of the nucleus. What I am unsure about is, if the electron has a potential energy of -13.6 eV, then does this mean that it has no kinetic energy? Because if it has kinetic energy, then this would mean that it would need less than 13.6 eV to become free of the nucleus because it already has some of the positive energy it needs. We teach that the closest the electron can get to the nucleus is when KE=PE. This occurs when r = bohr radius. So is the actual radius of the ground state electron greater than this so that we can reduce the kinetic energy required so that it has -13.6 eV of energy. Now of course, I know that we don't know the radius of the electron orbit. We can merely speculate and look at a probability distribution. I guess what my question could boil down to is: does the ground state electron have an overall energy of 0? Please help and be gentle. I am asking for this idea to be explained without any university physics!