 Today we're going to learn how to use orbital diagrams to describe the way that the electrons are organized within an atom. The orbital diagrams will show the energy level, the sub-level, and the number of electrons in each orbital. If you recall from the periodic table, we can use the sub-blocks are divided up on the periodic table with the first two columns being in the S sub-level, the next six being part of the P sub-level, the middle ten are part of the D sub-level block, and the bottom fourteen are part of the F block. So we are going to organize these electrons based on their sub-levels, where they lie, and also their period numbers, which is going to indicate their level number for some of the sub-levels. So if we choose an element, let's say oxygen. Oxygen has an atomic number of eight, which means it has eight protons and it also has eight electrons. So we have to organize our eight electrons. To organize our eight electrons, first we're going to start on the first energy level, which is going to be designated by our period number. So it's going to be energy level one. Our first, our only sub-level on the first energy level is S. So the first two electrons from hydrogen and helium will fill the one S sub-level. So if we use a box to represent our block, our orbital, one S, we're going to use arrows to represent our electrons. We're going to draw one arrow pointing up and one arrow pointing down. By drawing one up and one down, it represents that they have opposite spins and those electrons will not repel each other as much. So that takes care of the first two electrons for oxygen. If we go back to the periodic table, we'll see that that's the first row, the first two electrons. Now we're on to the second row of the periodic table. And the first sub-level that we come to on the second row is S. So that's going to be two S. S again has only one orbital. So one box, it can hold a maximum of two electrons. So now we have four electrons total that are organized, but we have to get to eight. And the next level and energy level after two S is two P. Now oxygen lies in that two P energy level and sub-level. It is actually the one, two, three, fourth element over. So that means there are going to be four electrons in the two P sub-level. The P sub-level doesn't have just one orbital. It contains three orbitals, so we're going to draw three boxes. And this is two P. When we organize our elements into this sub-level or our electrons, we're going to put one electron in each box first. So this will be our fifth, sixth, and seventh electrons. We're going to put them into each orbital individually first. And then any leftovers will come back and start pairing them up. So our eighth one, we will have to pair up in the first box. So this would be the correct orbital diagram for oxygen. What you would not want to do, if this was your two P sub-level, you would not want to put a pair in a pair and leave one box empty. You would want to do it the way I showed you originally, spread them out, put one electron in each box before coming back and making a pair. So this would be incorrect. So orbital diagrams actually show you the number of electrons in each orbital. If we choose another example, let's go back to the periodic table. And let's say we wanted to do sodium. Sodium has a total of 11 electrons. So for our orbital diagram, it has 11 electrons that we have to organize. So first level and sub-level, 1s, it contains one orbital. It can hold two electrons. The next level and sub-level is 2s, s contains one orbital. We can put two electrons in there. So that's four out of our 11. Next comes 2p, p contains three orbitals, 5, 6, 7, 8, 9, 10. That takes care of the first 10 electrons. If we go back to our periodic table, we'll see that sodium, well, after the 2p sub-level, we come to 3s. Now sodium is the first one in 3s, so it only has one electron. So our energy level and sub-level is 3s. We only have one orbital for an s sub-level. We're only going to put one electron in there because that makes all 11 that we need to organize. So those are examples of orbital diagrams. And this can be used to display the organization of your electrons within the atom.