“How can we measure the energy used when an electron is added?”
We know that the energy of an atom changes when an electron is added. But how can we measure so? Well, we know that electrons are always placed into orbitals. And we know that an element’s oxidation state is contingent upon the numbers of orbitals filled. And on top of that, the more orbital shells are filled, the smaller the radius becomes, therefore magnifying the force. So wouldn’t it make sense that it is easier for an electron if most of the valence shells are filled? Therefore, electrons become easier to add the higher occupancy of orbitals.This makes sense because as we move from left to right, elements tend to become more negative in their reactions. Scientists have termed this principle electron affinity.