Electron Details: the Filling of the SubshellsElectron Details: the Filling of the Subshells As you can see from the diagram below, each shell of the electron has one more subshell than the previous shell. You can also see that the number of electrons that can fit into each subshell is 2 for the first, or s subshell, 6 (2 + 4) for the second subshell (the d subshell, 10 (6 + 4) for the third and so on.
Now it becomes a simple matter of writing down the shell numbers and names in order as they are struck by our arrows. I will only present the first 10 here as an example. See if you can follow where these have come from on the diagram. 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 and so on. You can already see that not all the 3rd shell subshells are in order. This layering of subshells can also be seen in cross section like this:
ELECTRON DETAILS: HOW TO USE THIS WITH ELEMENTS Take an element from the periodic table, say Iron (Fe) which has 26 protons. In its neutral state Fe has 26 electrons (one for each proton). The second number for each subshell (eg, the "2" in 1s2) is the MAXIMUM number of electrons it can take. To get the electron arrangement for Fe, I simply fill in the subshells in the order given in the diagram until I run out of electrons, like this: I have 26 electrons to start with. 1s2 (2 electrons used to fill this, there are 24 remaining). 2s2 (2 electrons used to fill this as well, there are 22 remaining) 2p6 (6 electrons to fill this, there are 16 remaining) 3s2 (2 electrons to fill this, there are 14 remaining) 3p6 (6 electrons to fill this, there are 8 remaining) 4s2 (2 electrons to fill this, there are 6 remaining) 3d6 (there are only 6 available so only 6 can be put into the 3d subshell; it is NOT full) There are no electrons left over, so that is the end. Writing this all out together, we get this: 1s2 2s2 2p6 3s2 3p6 4s2 3d6 which is the electron arrangement for Iron (Fe) in its neutral, resting state. ELECTRON DETAILS: ONE MORE THING If we take these electron details and rearrange this last order numerically, we get this: 1s2 2s2 2p6 3s2 3p6 3d6 4s2 It is an interesting point that when thus rearranged, there is not one single element in the whole periodic table that has more than 8 electrons in its outer shell. These outer shell electrons are called the valence electrons and are the ones involved in all the bonding and chemical reactions of each atom. You can download that subshell filling diagram in PDF form: CLICK HERE. Return from Electron Details: the Filling of the Subshells to The Chemistry or return to the Green Planet home page for more Solar Power Facts.
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