AT_Electron Configurations Lesson

Electron Configurations

Now that you know how electrons fill the orbitals within a sub-level, let's learn the order in which they fill different energy and different sub-levels. The way that the electrons fill the orbitals is known as the electron configuration. Remember that the electrons determine much about the way that an atom behaves. Because they are so important, knowing the electron configuration will go a long way towards helping us understand atoms. An electron configuration shows the energy level, sublevel, and the number of electrons in that subshell.

ELECTRON NOTATION 3p5 3: Energy Level p: specific electron 5: orbital sublevel

Watch the following to learn how to write electron configurations for an element.

Noble Gas Configuration

After writing out the configuration for bismuth, you'll be glad to hear that there is a shortcut way to write electron configurations. This is called noble gas core configuration. As the name implies, it is based on the noble gas that is found before the element that you are writing.  

Noble Gas Core Configuration Here is the electron configuration for Chlorine (Cl): 1s2 2s2 2p6 3s2 3p5 Instead of writing this entire configuration, we can simply look backwards on the periodic table to the noble gas that is before it. The noble gas is Neon (Ne) - NOT Argon The configuration of Neon is 1s2 2s2 2p6 Write [Ne] in place of that part of the electron configuration. Make sure you use brackets! 1s2 2s2 2p 3s2 3p5 becomes [Ne] 3s² 3p5

Valence Electrons

The electrons that are on the outermost energy level are called valence electrons. These are not the electrons that are written last, but the ones that are in the highest energy levels. Look at the first few examples. The valence electrons have been highlighted - notice the energy level they are in.

*** A special note about the last example, you should have figured out that the element was Argon. If you have a noble gas, you cannot use only that element for the electron configuration. In other words, [Ar] is not the correct noble gas configuration for Argon, you have to go back to the noble gas that preceeds it and move forward. Thus, the correct noble gas configuration for Argon is [Ne] 3s2, 3p6

Watch the following video on valence electrons and electron configuration theory.

Now that you can write electron configurations, you will be able to answer a question like this. Is the gaseous atom of calcium paramagnetic? Remember from the previous page that paramagnetism occurs when there are unpaired electrons in an atom.   In order to answer this question, first write the electron configuration. 

Ca

Answer: [Ar]4s²

Now, draw the orbital diagram for the sublevel past the noble gas core electron configuration.

image of two arrows, one pointing up and the other pointing down

You can see that there aren't any unpaired electrons, so Ca is not paramagnetic.

Remember to work on the module practice problems as you complete each section of content.  

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