The elements that would have a greater tendency to become negative ions are the nonmetals. From the trends in the periodic table, the electron affinity tends to increase as you move from right to left which means that the likelihood of gaining electrons from right to left decreases. Most of the nonmetals are located in the right side of the periodic table which would mean they have more electron affinity which will give them the tendency to pull more electron towards them making them negative ions or what we called anions. Examples are chloride, flouride, bromide ions. Metals most likely form cations.
