Electron configuration

An electron configuration diagram is a useful tool to represent electrons in atoms. In this lesson, we will introduce this diagram and see how it works when electrons are added to the nucleus one by one. Students will also learn Hund's rule.

This lesson is a part of MEL Chemistry VR. Learn more →

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You have learned that elec­trons oc­cu­py spe­cif­ic or­bitals.

To­day we will use a spe­cial di­a­gram that will help us to un­der­stand the struc­ture of elec­tron or­bitals.

Let's take our sul­fur atom and check its elec­tron struc­ture again, this time us­ing this di­a­gram.

Ready to dive?

Here is our sul­fur atom with all its elec­trons.

And here is the di­a­gram show­ing all elec­tron or­bitals as small box­es.

Once again let's peel off all the elec­trons and add them back one by one, this time us­ing our di­a­gram.

Let's add our first elec­tron — it will go to the first or­bital that is called 1s.

Now look at the di­a­gram — we add an ar­row to the 1s box to show that we have one elec­tron on this or­bital.

Now let's add the sec­ond elec­tron — as you may re­mem­ber it will go to the same or­bital. Now look at the di­a­gram, we have added the sec­ond ar­row to the first box to show that there are two elec­trons on this or­bital.

Do you re­mem­ber, we learned that only two elec­trons can be on one or­bital but did not ex­plain why? Now it is time to ex­plain this rule.

Each elec­tron has a prop­er­ty called spin that can have only one of two pos­si­ble val­ues. On our di­a­gram, we show spin as ei­ther an up or down ar­row.

The fun­da­men­tal laws of physics say that two elec­trons can­not ex­ist in the same state. So, if they are in the same or­bital they must have dif­fer­ent spins. But there are only two pos­si­ble spin val­ues.

Now let's add more elec­trons and see how they are shown in the di­a­gram.

The next two elec­trons can fit in the sec­ond or­bital, called 2s.

The next three elec­trons will oc­cu­py three dif­fer­ent p or­bitals, one elec­tron per or­bital be­cause elec­trons re­pel each oth­er.

Look at the di­a­gram; we have three elec­trons in three box­es cor­re­spond­ing to our three dif­fer­ent p or­bitals.

Let's con­tin­ue adding elec­trons and see the changes in the di­a­gram.

When an elec­tron is added to an or­bital, we add an ar­row to the cor­re­spond­ing box on the di­a­gram.

Now our sul­fur atom is com­plete. The di­a­gram rep­re­sents its elec­tron struc­ture.

You can play with the di­a­gram by click­ing on dif­fer­ent box­es to see the cor­re­spond­ing elec­tron or­bitals.

Let's go back to our lab­o­ra­to­ry. Try to re­call the name of the first or­bital.

The first or­bital is called 1s.

Teacher's notes


atoms, elec­trons, elec­tron or­bitals, elec­tron con­fig­u­ra­tion, atom con­fig­u­ra­tion, elec­tron con­fig­u­ra­tion di­a­gram

Stu­dents will

  • Re­call that elec­trons in atoms oc­cu­py elec­tron or­bitals
  • Learn that there is a con­ve­nient way to write down an elec­tron con­fig­u­ra­tion by means of an elec­tron con­fig­u­ra­tion di­a­gram
  • Ex­am­ine a sul­fur atom and di­a­gram how elec­trons ap­pear to oc­cu­py or­bitals

Top­ics to dis­cuss

  • Rules for elec­trons: Pauli Ex­clu­sion Prin­ci­ple, Auf­bau Prin­ci­ple, & Hund's Rule
  • Elec­tron con­fig­u­ra­tion di­a­grams and the pe­ri­od­ic ta­ble


  • How to com­plete an elec­tron con­fig­u­ra­tion di­a­gram for dif­fer­ent atoms?


Please see be­low for the link to a Google form con­tain­ing a quiz on the ma­te­ri­al above.

This can be as­signed dur­ing class time or as home­work. The quizzes are marked and the sys­tem shows which ques­tions stu­dents get cor­rect and in­cor­rect. Please note that stu­dents should record their scores, as they will not be view­able lat­er.