We just learned how
Molecules are a bunch of atoms stuck together.
Another fun thing to learn about is
Chemical Elements.
These are the very simple types of atoms that make up all of the
molecules
that make up everything in the world.
So for example,
Oxygen is a chemical element, and so is
Hydrogen.
They're both types of
gases,
and they both are
atoms all by themselves.
But when these atoms get stuck together, they become a molecule and turn into water!
Every type of thing on the planet is made up of these
chemical elements,
from the dirt under your feet to the clouds in the sky.

(from: wikipedia -
chemical element)