Why it's easy to form a cation at low ionization energy?
Answers
As the atom become a cation,its number of electrons decreases(but notice that number of protons are same,and hence positive charge is more as compared to negetive charge).Since the number of electrons is less now, the effective nuclear charge has increased due to decrease in electron-electron repulsion.
As the number of electron decreases (which happen in a cation),the repulsion between the remaining electrons decreases. Since electron-electron repulsion make it easier to pull out a electron hence a decrease in electron-electron repulsion will contribute towards an increase in resistance of being pulled outside.
Conclusion: As you decrease number of electrons in atom by taking them out,effective nuclear charge increases, due to which electrons are bounded to nucleus strongly, making them hard to remove.