This is a topic which I have difficulty getting my head around (I'm about 3 years away from covering it in school), but it is my understanding that bonds between atoms with a large electronegativity difference (greater than or equal to 1.7) are usually considered to be ionic, while values between 1.7 and 0.4 are considered polar covalent. Therefore, a higher negativity means that the atom is more likely to ionize.....
I think...
What I can tell you though is that the number of electrons on the outermost shell affects ionization energy/discharge potential...If with 1,500 kJ/mol you removed one electron and required 6,000 kJ/mol to remove another electron and then 5,000 kJ/mol, etc, the element would have had one electron in its outermost shell. (Must be a metal) then...
Look at this link:
Ionization potential - Wikipedia, the free encyclopedia