 Today we're going to be learning about how electrons are organized within an atom. Electrons in an atom are organized into different levels, sub-levels and orbitals within the atom. So the first step is to learn about the energy levels. The energy levels, basically, if we have the nucleus, the energy levels of an atom are kind of like concentric circles going around the nucleus. It would actually be three-dimensional. But the energy level that is closest to the nucleus would be designated energy level one. The next energy level would be energy level two and so on and so forth. And if we drew a fourth one, it would be energy level four. So these are the main energy levels. Each level can hold a specific number of electrons. So once the first energy level is full, then we would start to put electrons on the second energy level. And when it is full, we'd move to the third energy level and begin to fill it, and we would do this consecutively. So our energy levels, we have energy level one, two, three and four. So for energy level one, every energy level is subdivided into sub-levels. The sub-levels actually have letter designations. In energy level one, we have one sub-level and it's designated letter S. For energy level two, we have two sub-levels. We have S and we have P. For the third energy level, we have three sub-levels, S, P and D. And for the fourth energy level, we have four sub-levels, S, P, D and F. So whatever the energy level number is, that's how many sub-levels there are. These sub-levels are then again divided into orbitals. Orbitals are the areas where you're most likely to find the electrons in the atom. Each sub-level has a specific number of orbitals. The S sub-level contains one orbital. The P sub-level contains three orbitals. The D sub-level contains five orbitals. And the F sub-level contains seven orbitals. These orbitals are kind of like the rooms where you're most likely to find those electrons in the atom. Those orbitals, each orbital can hold a maximum of two electrons each. So we can determine how many electrons each sub-level and level can hold. So number of electrons per sub-level. If each orbital can hold a maximum of two electrons, the S sub-level has one orbital. It can hold two electrons. So two electrons for the S. The P has three orbitals, so it can hold two electrons in each orbital, which gives you a total of six electrons. The D sub-level has five orbitals, so it can hold a maximum of ten electrons. And last but not least, the F. F can hold a maximum of fourteen electrons. So all of the electrons that are part of an atom are going to be organized into a level and a sub-level. We're going to fill them by starting with our lowest energy level first and then the lowest sub-level. When it's full, we move to the next energy level, fill the first sub-level, then we fill the second sub-level, and then we move to the next energy level, and we'll move through these and fill each consecutive level. The order of the filling is actually not the same as listed on this chart. We will go to the periodic table to discuss how these different levels and sub-levels are filled. There we go. So on the periodic table, we can actually divide the periodic table into our different sub-level groups. If you look at the first two columns of the periodic table, which we have highlighted, and it also includes helium, which is over on the right side of the periodic table, these make up your S-block elements. So that means the last electron in their atom is going to be in the S-block, your sub-level. The P-block are these six columns over here, and that means the last electrons in that atom will be in the P-sub-level. The D-block are the middle elements here, and they represent the transition elements. Their last electrons, as we do our organization scheme, will end up in the D-sub-level. And last but not least, we have our F-block down here. The lanthanides and actinides are part of the F-block. So if you recall, our S-sub-level elements can hold a maximum of, those orbitals can hold a maximum of two electrons. So these are the first two columns. Our P-sub-levels can hold a maximum of six electrons. So if we look at our P-sub-block, we have one, two, three, four, five, six columns. Those would be the six electrons that would fill the P-block for that energy level. The D-block, D-sub-level can hold a maximum of ten electrons. There are ten columns across the D-block here. So that means that these electrons would fill the D-sub-level. And last but not least, we have our F-block again. F has seven orbitals, can hold a maximum of fourteen electrons. And there are fourteen elements across here. So those would be our fourteen electrons that would fill the F-block. From this information about how the elements are organized, we can then do orbital diagrams and electron configurations, which will be the next way that we'll use this information.