Atom structure

In this lesson, you will learn that an atom consists of a tiny atomic nucleus surrounded by an electron cloud. We will discuss the three main subatomic particles: protons, neutrons and electrons, and their properties.

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

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In the pre­vi­ous lessons, we have seen that all mat­ter is built out of small atoms. But what are atoms them­selves? What's in­side them?

We will start with our he­li­um bal­loon.

Let's look in­side. Ready to dive?

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

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

You see that this atom con­sists of an atom­ic nu­cle­us sur­round­ed by an elec­tron cloud. That is how atoms are made.

The nu­cle­us is pos­i­tive­ly charged and elec­trons are neg­a­tive­ly charged, so they at­tract each oth­er.

The real nu­cle­us size is much small­er than you see here. Let's show its real size.

It is now small­er than one pix­el on your screen.

It is about hun­dred thou­sand times small­er than the size of an atom.

Nev­er­the­less, al­most all of the atom's mass, over 99.9% of it, is found in the nu­cle­us.

Let's zoom in to get a good look at this nu­cle­us.

Now you can see that the nu­cle­us con­sists of pro­tons and neu­trons tight­ly bound to each oth­er.

The pro­tons are pos­i­tive­ly charged so they ac­tu­al­ly at­tract elec­trons.

The neu­trons are not charged at all.

Let's go back to our atom.

Lat­er, we will show the nu­cle­us blown up, just to make it eas­i­er to see. Just re­mem­ber that an ac­tu­al nu­cle­us is much much small­er.

Now we will look at an­oth­er atom.

Please point at the atom­ic nu­cle­us.

Now point at the elec­trons.

Now, let's get clos­er to the atom­ic nu­cle­us again.

Point at a pro­ton.

Pro­tons are pos­i­tive­ly charged; you can see a small plus sign on them.

Now point at a neu­tron.

A neu­tron has zero charge. Pro­tons and neu­trons are al­most of equal mass and both are more than a thou­sand times heav­ier than an elec­tron.

Let's go back to our lab­o­ra­to­ry.

Which of these par­ti­cles at­tracts a pro­ton?

A neg­a­tive­ly charged elec­tron will at­tract a pos­i­tive­ly charged pro­ton.

Which of these par­ti­cles will be re­pelled by a pro­ton?

Same charged par­ti­cles will re­pel one an­oth­er. So, two pos­i­tive­ly charged pro­tons will re­pel each oth­er.

Teacher's notes


atoms, elec­trons, nu­cle­us, pro­tons, neu­trons, coulomb forces

Com­mon mis­con­cep­tions

  • Grav­i­ty is one of the forces pulling nu­clei and elec­trons to­geth­er.
  • Plan­e­tary mod­el: elec­trons move around the nu­cle­us.

Stu­dents will

  • Learn that the atom con­sists of a pos­i­tive­ly charged nu­cle­us and neg­a­tive­ly charged elec­trons
  • Learn that a nu­cle­us con­sists of pro­tons and neu­trons
  • Learn about the forces that bring nu­cle­us and elec­trons to­geth­er
  • See that elec­trons spread around the nu­cle­us like a cloud
  • Learn that the nu­cle­us is much heav­ier than elec­trons
  • Learn the rel­a­tive dis­tance from the nu­cle­us to elec­trons com­pared to nu­cle­us size

Hands-on ac­tiv­i­ties

Af­ter VR

The aim is to give stu­dents an idea that the nu­cle­us is much heav­ier than elec­trons.

Ask stu­dents to weigh a 2-litre bot­tle of wa­ter. Then cal­cu­late the weight of an elec­tron, as­sum­ing that the bot­tle weight rep­re­sents the mass of a pro­ton. Ask stu­dents to weigh a piece of play­dough rep­re­sent­ing an elec­tron.

His­to­ry and sources of knowl­edge

Top­ics to dis­cuss

  • How and where atoms are formed.
  • It’s not cor­rect to say that atoms are most­ly an emp­ty space.
  • The weight of pro­tons and neu­trons as com­pared to elec­trons.

Fun facts and quotes

  • The largest an­i­mal that now ex­ists on Earth is a blue whale. Its length is up to 30 me­tres and a weight of up to 180 tons. If we re­place all the atoms that form a blue whale with their nu­cle­us the length of the an­i­mal would be 0.3 mm (it's close to the small­est ob­ject we can see with naked eyes). And the weight would not change at all.
  • In neu­tron stars, all mat­ter is denser (up to 10 times) than in an atom nu­cle­us.
  • The force of grav­i­ty be­tween the nu­cle­us and elec­trons is 1 and 42 ze­ros weak­er than the elec­tro­stat­ic force ac­tu­al­ly hold­ing them to­geth­er.
  • Most of the atoms in the uni­verse are from su­per­no­va ex­plo­sions.


  • Name sub­atom­ic par­ti­cles.
  • Which sub­atom­ic par­ti­cles are charged?
  • Which sub­atom­ic par­ti­cles are not charged?
  • Which is heav­ier elec­tron or neu­tron?
  • Which is heav­ier elec­tron or pro­ton?
  • What is the force hold­ing nu­cle­us and elec­trons to­geth­er?


The elec­tron is ap­prox­i­mate­ly 2,000 times lighter than a pro­ton. Cal­cu­late the mass of an elec­tron as a per­cent­age of the pro­ton mass.