Always in MotionAs you know, electrons are always moving. They spin very quickly around the nucleus of an atom. As the electrons zip around, they can move in any direction, as long as they stay in their shell. Any direction you can imagine — upwards, downwards, or sidewards — electrons can do it. Electrons are constantly spinning in those atomic shells and those shells, or orbitals, are specific distances from the nucleus. If you are an electron in the first shell, you are always closer to the nucleus than the electrons in the second shell.
Shell BasicsLet's cover some basics of atomic shells:
1. The center of the atom is called the nucleus.
2. Electrons are found in areas called shells. A shell is sometimes called an energy level.
3. Shells are areas that surround the center of an atom.
4. Each of those shells has a name (K, L, M...).
There are a couple of ways that atomic shells are described. The most general terms are the basic regions where you find electrons. Chemists use an "n" value, or the letters K, L, M, N, O, P, and Q. The "K" shell is the one closest to the nucleus, and "Q" is the farthest away. For simple atoms, those "n" values usually match the row number on the periodic table and are also known as energy levels. The second description looks at how electrons act inside of the shells. There are certain patterns of movement. Chemists have described those patterns with the "l" value. The "l" values tell you what suborbital an electron is found in. You will see the lowercase letters s, p, d, f, g, and h for the suborbitals.
For example, the electron in a hydrogen (H) atom would have the values n=1 and l=0. The single electron would be found in the "K" shell and the "s" suborbital. If you go on to learn about chemistry, you may see its description written as 1s1. Helium (He) is still in the K shell (top row), but it has two electrons. The first electron would be 1s1 and the second would be 1s2. What about lithium (Li) at atomic number three with three electrons? It would be described as 1s2 2s1. Why is that?
Not all shells and suborbitals hold the same number of electrons. For the first eighteen elements, there are some easy rules. The K shell only holds two electrons. The L shell only holds eight electrons. The M shell only holds eight electrons. The M shell can actually hold up to 18 electrons as you move to higher atomic numbers. The maximum number of electrons you will find in any shell is 32.
Suborbital BasicsWe talked a little bit about s, p, d, f, g, and h suborbital descriptions. While the electrons are found in energy levels and regions around the nucleus, they can also be found in special areas within those energy levels. A guy named Schrödinger started realizing that all electrons weren't the same and they didn’t move in the same way. So, looking back at lithium we saw 1s2 2s1.
Those values describe where you can find the three electrons. Two are in energy level one in suborbital s. The third electron is in energy level two and suborbital s. Are they both in the same suborbital s? No. The letter of the suborbital references the shapes of regions you will find electrons. Suborbital "s" is in a spherical shape. Suborbital "p" is shaped kind of like barbells or a figure eight. Then you have "d" with two possible shapes, and it just gets crazy from there. Just remember that those letters refer to regions where you are likely to find the electrons within their energy level.
One last example: silicon (Si) at atomic number 14. You have fourteen electrons. Written out the long way, it looks like 1s2 2s2 2p6 3s2 3p2. Do you see how the numbers add up to fourteen? Row one has a shell that can hold two electrons. That’s covered by 1s2. Row two of the periodic table corresponds to shell two, which can hold eight electrons. You can see those eight in 2s2 and 2p6. Finally, we have shell/row three. Since suborbitals can only hold so many electrons, you see them divided into "s" and "p". Silicon only has four electrons in the third shell. Suborbital "s" can hold two, and the other two are found in "p". When you get past argon (Ar) at atomic number 18, you will start finding the "d" suborbitals in the transition elements.
Where Are the Electrons?We've been telling you that electrons reside in specific shells or move in specific patterns in suborbitals. We can't really tell you exactly where an electron is at any moment in time. We can only approximate, or guess, where an electron is located. According to something called quantum theory, an electron can be found anywhere around the nucleus. Using advanced math, scientists are able to approximate the general location of electrons. These general areas are the shells and suborbitals.
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Researchers Create “Designer Electrons” (Stanford Univ. Video)
Useful Reference MaterialsEncyclopedia.com (Molecular Orbitals):