The energy released when a ground state gas atom of an element gets an electron to become a monovalent gaseous negative ion is called the electron affinity (Y) of the element. The electron affinity of an element represents the energy released when an electron is formed to form a negative ion; if it is a negative value, it means the energy to be absorbed (the affinity energy is usually a metal, and it is difficult to form a negative ion).
The electron affinity is a measure of the oxidation of an element. The greater the electron affinity, the greater the tendency of the atom to gain electrons, the stronger the non-metallicity of the corresponding element of the atom, and the less regularity of the electron affinity .
Due to the limitation of conditions, there is no accurate measurement method for electron affinity. The electron affinity of different literatures vary greatly, and it does not show periodic changes. Therefore, the application of electron affinity is not widespread.