What wavelength of light ,λ, would be necessary to ionize an electron at n = 2 in a hydrogen atom? In my notes there are two equations that seem relevant to my question they are: E=hc/λ and -2.18 x 10-18 J((Z^2/n final^2)-(Z^2/n initial^2)) where h is planks constant, c is the speed of light, Z is the atomic number of the element, in my case hydrogen, and n is the state the electron is in. I think it means energy state. I tried to think of something, but I don't know. What does it mean by ionizing an electron??