A student recently asked me why successive electron affinities can have negative values. Here’s a quick explanation:
First, let’s clarify what we mean by successive electron affinity. It refers to the energy change when adding a second, third, or subsequent electron to an already negatively charged ion, after one electron has been added to the neutral atom.
Now, here’s why successive electron affinities have negative values: Once an atom has gained an electron and become a negatively charged ion (anion), it resists gaining additional electrons due to the repulsive forces between the negatively charged particles. This repulsion is why the energy change for adding more electrons—successive electron affinities—often have negative values.
