The Tiny Particles That Make Up All Substances

Sara: The stuff inside this old lab thermometer that expands and shrinks when the temperature changes is called mercury?

Marko: That's right. But you should be careful with mercury — it's a poisonous substance.

Sara: Thanks for the warning, but this is just an imaginary experiment. So imagine a tiny drop of mercury sitting on a table, like a little silver ball. Could we split that mercury ball into two smaller ones?

Marko: We could.

Sara: And then split each of those again, and again, and again…

Marko: Yep, we could keep dividing that drop into smaller and smaller bits, many, many times.

Sara: And no matter how many times we split it, it would still be mercury?

Marko: Hmm… not forever. Eventually, we’d get to a point where we hit the tiniest bit of mercury we could no longer split easily. And if we did split it again, it wouldn't be mercury anymore.

Sara: So that means there’s such a thing as... the tiniest bit of a substance?

Marko: Exactly. Every substance is made up of very tiny particles that have the same properties as the substance itself — and they are the substance.

Sara: I even know what those particles are called in science 😎

Marko: I bet you do — it's a pretty famous science word. But let’s not say it just yet. We'll dive into it properly in another lesson.

Sara: They're called atoms, molecules, and ions!

Marko: SARA!

Sara: Okay, okay, I’ll stop! Let’s just call them “particles” for now.

Marko: Deal. We’ll say every substance is made of tiny particles — and in science, they have fancy names like atoms, molecules, and ions.

Sara: MARK!

Marko: Oops, sorry! Right. Just... “particles.” The tiniest bits of a substance that still are that substance.