For the rest of the principal energy levels and their sublevels, look at the following table. Notice the numbering of each sublevel and how all have an s sublevel.

Notice that there are s, p, d, f, g, h, and so on sublevels. For the remainder of this tutorial, we will focus only on the s, p, and d orbitals. Now that we can see the different sublevels available, what does this mean in terms of energy? As mentioned earlier, the 1s energy level is always the lowest energy level of all principal energy levels. Furthermore, for each principal energy level, the s sublevel is also the lowest energy sublevel. Thus, you may think the order of sublevels in increasing energy order would be 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f, and so on. However, the actual order is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 4d, etc. Notice that the 4s overlaps between the 3p and 3d. This is because of the 4s sublevel has more energy than the 3p yet less than that of 3d. The diagram below illustrates the determination of order of sublevels by increasing energy.

Now that you understand the different sublevels that exist in atoms, let us explore orbitals. An orbital is a region within a sublevel where electrons may be found. In each orbital, there can be a maximum of two electrons. Each s sublevel has a single orbital. Each p sublevel has 3 orbitals, each d sublevel has 5 orbitals, and each f sublevel has 7 orbitals. Thus, any s sublevel can have two electrons, while any p sublevel can have 6 electrons, and so on. Observe the following relationships in the table.

No. of sublevels	No. of orbitals (s, p, d, f)	Total No. of orbitals	Maximum no. of electrons
1 2 3 4	(1) (1, 3) (1, 3, 5) (1, 3, 5, 7)	1 4 9 16	2 8 18 32

To easily remember the relationship, let us assign the variable 'n' to the number of sublevels. So if there are 3 sublevels, n=3. There will be one s orbital, 3 p orbitals, 5 d orbitals. The total number is 1 + 3 + 5 = 9 which is n squared. In other words, the number of orbitals in all is the number of sublevels squared! Furthermore, the number of electrons in all is two times n squared for any number n.

There is also a very interesting relationship between these numbers and the periodic table. Notice in the first row, there are two elements, hydrogen and helium. The second and third row have 8 elements. The third and fourth rows have 18 elements and the fifth and sixth rows have 32 elements (with the lanthanide and actinide series, respectively).

To view an interesting periodic table, click here.

In the next section, we will see the different orbital shapes and how they are important. Click on 'Next Section' to continue.