The energy released when an electron is added to a neutral gaseous atom is called the electron affinity of the atom. Electron affinity is a measure of the energy change that occurs when an electron is added to a neutral atom in the gas phase to form a negative ion. This property is important in understanding the chemical behavior of atoms. It can either release energy, indicated by a negative value, meaning the process is exothermic, or absorb energy, indicated by a positive value, indicating an endothermic process.