1. The problem statement, all variables and given/known data For the hydrogen atom, determine the principle quantum number corresponding to an orbital of radius Rn=0.01mm 2. Relevant equations I'm using the following formula: Rn=(n^2)(Ao)/Z Where Rn is the orbital radius (0.01mm), n is the principle quantum number (wanted) Ao is a constant (0.5*10^-10) and Z is the atomic number (for hydrogen =1) 3. The attempt at a solution By converting Rn into metres and subbing in all the other values I obtain a value of n=447.2135955. Obviously there are two discreptancies: 1) n is not a whole number 2) it is abnormally large Can anybody show me where I have gone wrong?