That's a total of 18 electrons. The first 18 electrons are nice and easy, because they fill the orbitals in order. First, all of the n = 1 orbitals get filled, then all of the n = 2 orbitals get filled, then the n = 3 orbitals get filled. From the 19 th electron on, though, things get a little crazy! Before we move on to the that region beyond 18 electrons, let's take a brief look at a shorthand notation that scientists use to signify the electron orbital filling of a given atom.