Because of the imbalance of charge the system will have a net charge that is positive. Consequently, any positively charged system is referred to as a cation. Electron Affinity is a measure of the desire or ability of an atom to gain electrons. It is an energy concept. The formal definition states that Electron Affinity is the amount of energy released when an electron as added to an atom.
Most atoms tend to lose energy when they gain electrons.
Some atoms do not. Those that do not tend to appear in the lower left corner of the Periodic Chart. The concept of Electron Affinity tends to be viewed as an exothermic process. The elements located in the upper right corner of the Periodic Chart have the high E.A. values while those in the lower left corner have the low E.A. values. This is interpreted as meaning that elements in the upper right corner are usually found an anions while those in the lower left corner are usually not found as anions.