Electron configuration

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.