Go back to the periodic table and study it carefully. You will see that ionization increases from left to right across a period. It decreases down a given group. As for atomic radi, you will see that it decreases across a period from left to right but as you reach towards the noble gases, you will see that their atomic radi are larger. In such circustance, the ionization energies of noble gases should be lower but it won't because they have already attained their octet structure and will hardly loose electron. Therefore, their ionization energy are high.