Highly excited atoms have electrons with large principal quantum numbers. Such Rydberg atoms have unique properties and are of interest to astrophysicists. For hydrogen atoms with large n, derive a relation for the separation of energy levels. Calculate this separation for n=100; also calculate the average radius, the geometric cross section, and the ionization energy. Could a thermal collision with another hydrogen atom ionize this Rydberg atom? What minimum velocity of the second atom is required? Could a normal-sized neutral H atom simply pass through the Rydberg atom leaving it undisturbed? What might the radial wavefunction for a 100s orbital be like?