Lesson 12: Electrons, Atom Models, and the Periodic Table

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After a hectic week, you will be happy to hear we don’t have a lab to write up in your notebooks for this lesson. That means you don’t have to bring your goggles or gloves either. You do, however, need to really focus on the readings in the textbook because this lesson is critical for your understanding of chemistry.

Textbook Reading: Finish Chapter 9, sections 9.5-9.9 on pages 294-315.




Electrons are where all the action is in chemistry. By developing sophisticated and complex models of atoms that explain electron behavior, chemists have a powerful tool to understand molecular structures and chemical reactions.

Our most recent model of the atom comes from the study of quantum mechanics. The theory and math behind the model are pretty complex, but chemists have been pulling out some basic concepts that can be extremely useful. Remember, however, that this is a model and may be modified as our understanding increases.


We have some awesome videos this week to supplement your textbook.

Let’s start out with a TED video about the uncertain location of electrons.

Although this video suggests orbitals are where electron can be found 95% of the time, other representations of orbitals are often where the electrons are found 90% of the time. In any case, you can think of orbitals as boxes or rooms where electrons are found most of the time. You should also remember that each orbital can only hold two electrons.

For the musicians in the class, this Crash Course video has an explanation of electrons that might just “resonate” with you šŸ™‚



Okay, if you don’t know enough about music to understand his analogy, then we can use a simpler analogy.


(Illustration of single electron orbitals from UC Davis ChemWiki, licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.)

Orbitals are grouped around the nucleus in very specific ways, based on the number of electrons and their energy states. The groupings are given names: shells and subshells. If orbitals are rooms where electrons are found most of the time, then subshells are clusters of rooms. You might think of them as one apartment in a large apartment building, or one set of offices in an office complex.

Continuing the building analogy, the shells would be the different floors of the building. The higher floors have more energy and contain more subshells.

The shells and subshells fill with electrons in a very orderly way, so that we can figure out the electron configuration of atoms of each element in the periodic table simply based on the number of electrons it contains. The electron configuration, although it looks complicated, is simply the arrangement of the electrons.

Bozeman Science has a serious explanation of electron configurations. He relates the configurations to “ionization energy” or how hard it is to pull an electron off an atom.

Isn’t the idea that the p orbitals fill like seats on a bus helpful?

Still unsure what all this means? Don’t worry, we’ll being going over it all in class. Be sure to write down your questions and bring them with you.

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