I am studying for my exam and I have run in to this problem. The problem is given here ,[/PLAIN] [Broken] it is #9. I don't understand why -e ≠ ∫ρdV from 0 to the bohr radius, a0. If all of the charge is contained within that volume. I may not be understanding where exactly the Bohr radius is being measured to. I am thinking the a0 is the radius of the electron cloud. So the electron cloud would be a sphere with radius a0 with a charge of -e.