In this lecture, I'd like to talk about the concept of electron configuration. But before we get into that, it's really important to talk about the following principle known as the AFP principle. Now, this principle will help us explain electron configuration. Now, what this principle states is the following. Whenever an atom adds a new proton to create a new atom element, it must also add another electron to neutralize that extra charge that comes from that extra proton. So the problem is the following whenever we add a proton, we know exactly where our proton goes.