Electron orbitals

Electrons in an atom behave very differently. You will see that when an electron becomes a part of the atom, it is spread around the nucleus like a cloud, and you will see the shape of S and P orbitals. Later, you will learn the Pauli Exclusion Principle that states that only two electrons can share the same orbital. In this lesson, chemical symbols for elements are introduced.

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

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In the pre­vi­ous les­son you saw that an atom con­sists of a tiny nu­cle­us sur­round­ed by an elec­tron cloud.

But what is this elec­tron cloud? In­deed, it is one of the most im­por­tant con­cepts in chem­istry.

To un­der­stand elec­tron be­hav­iour is to un­der­stand why iron rusts, but gold does not,

why we can breathe oxy­gen, but not he­li­um.

In the pre­vi­ous les­son, we saw elec­trons in a he­li­um atom. Let's take some­thing with big­ger atoms to­day. Like our pen­cil.

Let's look in­side. Ready to dive?

We have to zoom in a bil­lion times to see in­di­vid­u­al car­bon atoms.

Let's choose one of those atoms and get clos­er.

You can see that in a car­bon atom the nu­cle­us is larg­er than in a he­li­um atom and we see more elec­trons. And they have strange fun­ny shapes.

Let's take apart our car­bon atom to see what this atom is made of.

This car­bon atom con­sists of 6 elec­trons – neg­a­tive­ly charged par­ti­cles; 6 pro­tons – heavy, pos­i­tive­ly charged par­ti­cles; and 6 neu­trons that have al­most the same mass as pro­tons but have no charge.

Now let's re-as­sem­ble it. First, we will make a car­bon atom nu­cle­us with 6 pro­tons and 6 neu­trons.

We chemists write a spe­cial sym­bol C_6_12 to show that this car­bon atom con­tains 6 pro­tons and that to­tal atom­ic mass is 12 which is the num­ber of pro­tons and neu­trons com­bined.

As you al­ready know, elec­trons are so light that we do not take them into ac­count.

And now the most in­ter­est­ing thing. Let's start to add elec­trons one by one and see what hap­pens.

We start with the first elec­tron. A neg­a­tive­ly charged elec­tron is at­tract­ed to the pos­i­tive­ly charged nu­cle­us.

But when the elec­tron be­comes a part of the atom, it is spread around the nu­cle­us like a cloud, and we call it an or­bital.

Does that sound weird? That is how na­ture works at an atom­ic lev­el.

Now let's add the sec­ond elec­tron. It will take the same place as the first elec­tron. The first two elec­trons will share their or­bital.

And here is an­oth­er new fact. Only two elec­trons can share the same or­bital.

Look what hap­pens when we add the third elec­tron. It can­not go into the or­bital where there are al­ready two elec­trons. So it has to go to the next or­bital.

Now just look what hap­pens to the oth­er elec­trons when we add them one by one.

Dur­ing the next few lessons you will see why elec­tron or­bitals are or­ga­nized in this way.

This mi­croscale world is very dif­fer­ent from the one we know.

Let's go back to our lab­o­ra­to­ry.

In this les­son you have seen an atom of car­bon. In the pre­vi­ous les­son you saw an atom of he­li­um con­tain­ing two pro­tons, two neu­trons and two elec­trons.

What will be the to­tal mass of that he­li­um atom?

The to­tal mass will be four atom­ic mass units.

Pro­tons and neu­trons have al­most the same mass, and we count each of them as one atom­ic unit.

An elec­tron is more than a thou­sand times lighter, so we ig­nore the elec­trons' mass.

Teacher's notes


atoms, elec­trons, elec­tron cloud, elec­tron or­bitals, or­bital shape

Com­mon mis­con­cep­tions

From the Bohr-Ruther­ford di­a­gram:

  • Elec­trons are mov­ing around the nu­cle­us
  • The size of an elec­tron is rough­ly the same as that of a pro­ton and neu­tron
  • The 'dis­tance' from the nu­cle­us to elec­trons and be­tween elec­trons

Stu­dents will

  • Learn that the nu­cle­us is sur­round­ed by elec­tron clouds
  • Be in­tro­duced to or­bitals
  • Learn that two elec­trons can share one or­bital
  • Or­bitals have dif­fer­ent shapes and sizes

His­to­ry and sources of knowl­edge

  • His­to­ry from Ruther­ford to Bohr and mod­ern the­o­ry.
  • Quan­tum the­o­ry: de­scrip­tion, com­pu­ta­tion­al mod­els.
  • Sci­en­tif­ic ap­proach: the best sci­en­tif­ic ex­pla­na­tion is based on ev­i­dence (ob­ser­va­tions) and sci­en­tif­ic knowl­edge. The the­o­ry should ex­plain the ob­ser­va­tions and make pre­dic­tions.

Top­ics to dis­cuss

  • Dis­cuss how we can trust the­o­ries about things we can't see.
  • The best sci­en­tif­ic ex­pla­na­tion is based on ev­i­dence (ob­ser­va­tions) and sci­en­tif­ic knowl­edge.

Fun facts and quotes

  • How and why atom mod­els de­vel­oped? A sci­en­tif­ic ap­proach re­quires cor­rect­ing a hy­poth­e­sis if new find­ings (ob­ser­va­tions, mea­sure­ments) are not ex­plained by an old one.
  • How can we trust the­o­ries about things we can't see?
  • Emis­sions and the ab­sorp­tion spec­tra of el­e­ments as the source of in­for­ma­tion about en­er­gy lev­els.
  • En­er­gy lev­el con­cept.
  • Lad­der with a fixed po­si­tion anal­o­gy: like climb­ing the lad­der with the fixed po­si­tion you can only step on these po­si­tions, but not in be­tween them. Elec­trons like­wise can have only cer­tain en­er­gy lev­els. In this case, the lad­der steps would be much small­er and clos­er to the top.
  • Quan­tum the­o­ry.


  • What’s the dif­fer­ence in shape be­tween s- and p- or­bitals? (sym­me­try de­scrip­tion)


  • How many elec­trons do the first 3 no­ble gas­es have? With an ex­pla­na­tion.