Question

How does ionization energy change with regard to distance to nucleus?

Answer 1

The farther away from the positively charged protons within the nucleus, the less energy is required to remove an electron because the positive pull on the electrons is weaker relative to distance

Answer 2

you can see this in the periodic table as you observe the size of the atom increase in groups from left to right

Answer 3

Well, as you move down in a group in periodic table number of shells and consequently the size of the atom increases. The inner shells cause shielding effect which reduces the force with which nucleus holds the outermost electrons. since ionization energy is proportion to this force, so it decreases with increase in size of atom.
If you look in a period from left to right number of shells in period remains the same but charge on nucleus increases which pulls the electrons more strongly which results in smaller size of the atoms and greater ionization energy.