During a journey inside different materials (water, sugar, etc.) you will see that the atoms in them arranged in bigger groups called molecules.

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To­day in our lab we have di­a­mond, salt, and an ice cube.

Re­mem­ber that a di­a­mond con­sists of car­bon atoms. Each atom is strong­ly bond­ed to four oth­ers and the atoms are ar­ranged in a spe­cif­ic or­der.

Salt is an ion­ic sub­stance. In salt, sodi­um ions and chlo­ride ions are packed in a reg­u­lar ar­ray.

But what will we see in­side ice?

Let's look in­side.

We see two types of atoms here: oxy­gen and hy­dro­gen.

They are grouped in groups of three atoms.

In­side one group atoms are bond­ed to each oth­er.

These groups are called mol­e­cules; wa­ter mol­e­cules in this case.

Each wa­ter mol­e­cule con­tains one oxy­gen and two hy­dro­gen atoms con­nect­ed by strong bonds. We show them by sticks be­tween atoms.

Con­nec­tions be­tween mol­e­cules are many times weak­er and are eas­i­ly bro­ken by heat­ing.

Let's go to the lab and look at the melt­ing ice.

So when you pick up ice in your warm hand, the con­nec­tions be­tween mol­e­cules are bro­ken and it turns into liq­uid wa­ter.

What do you think, do wa­ter and ice con­sist of the same mol­e­cules or not?

Yes, they do. Heat from your hands is not enough to break wa­ter mol­e­cules.

Now check out some­thing else.

On the ta­ble, you see the or­di­nary sug­ar.

Let's look at its mol­e­cules.

Do you see the su­crose mol­e­cules?

These mol­e­cules are much big­ger than wa­ter mol­e­cules.

Look at one of them.

Each mol­e­cule con­tains 12 car­bon atoms, 22 hy­dro­gen atoms, and 11 oxy­gen atoms.

Point to a car­bon atom in this mol­e­cule.

Let's look at some oth­er mol­e­cules of sub­stances you know.

Some mol­e­cules are small, like this oxy­gen mol­e­cule, that con­sists of just two oxy­gen atoms.

This is a mol­e­cule of meth­ane, the main com­po­nent of nat­u­ral gas.

And here is a mol­e­cule of acetic acid. The so­lu­tion of this acid in wa­ter is called vine­gar.

Some mol­e­cules are much big­ger, like this caf­feine mol­e­cule found in cof­fee, tea, and cola.

Try to count how many atoms are in this caf­feine mol­e­cule?

You saw that, in some sub­stances, atoms are grouped into mol­e­cules.

These sub­stances are called molec­u­lar sub­stances.

Let's go to the lab again.

The small­est mol­e­cule in the world is a hy­dro­gen mol­e­cule. It con­sists of two hy­dro­gen atoms.

One of the big­gest mol­e­cules in the world is DNA, it can con­tain hun­dreds of bil­lions of atoms.

There are as many atoms in one mol­e­cule of DNA as there are stars in a typ­i­cal gal­axy.

Teacher's notes


mol­e­cules, atoms, bonds

Stu­dents will

  • Learn that near­ly all sub­stances con­sist of mol­e­cules
  • Find out that bonds be­tween mol­e­cule atoms are strong and bonds be­tween mol­e­cules are weak
  • Find out that mol­e­cules can be small and large

Hands-on ac­tiv­i­ties

Af­ter VR

Ask stu­dents to heat two sub­stances (ta­ble salt and crys­tals of an or­gan­ic com­pound, such as sug­ar, ben­zoic acid, etc.) with a low melt­ing point. Af­ter the ex­per­i­ment, ask the stu­dents which sub­stance is more prob­a­ble to be molec­u­lar and why.

His­to­ry and sources of knowl­edge

  • The law of def­i­nite pro­por­tions was a big step to­wards the un­der­stand­ing of chem­i­cal com­pound for­ma­tion.
  • Mod­ern meth­ods of anal­y­sis like spec­troscopy and mass-spec­trom­e­try show molec­u­lar com­po­si­tion.

Top­ics to dis­cuss

  • Par­tic­u­late na­ture of mat­ter (par­ti­cles can be atoms, ions or mol­e­cules).
  • The forces that keep atoms in mol­e­cules to­geth­er. The forces that keep mol­e­cules to­geth­er.

Fun facts and quotes

  • There are up to 2 tril­lion mol­e­cules in one hu­man cell. More than half of this num­ber are wa­ter mol­e­cules.
  • When you tear off plas­tic like poly­eth­yl­ene or polypropy­lene you ac­tu­al­ly tear off its mol­e­cules.
  • Near­ly all or­gan­ic com­pounds are of molec­u­lar struc­ture.
  • Most smelly sub­stances are of molec­u­lar struc­ture.


  • Which are stronger bonds be­tween atoms in a mol­e­cule or bonds be­tween mol­e­cules?


Cal­cu­late the num­ber of atoms in­side a mol­e­cule (hy­dro­gen, wa­ter, acetic acid).