What are chemical substances?

A chemical substance is something made up of tiny building blocks that all look the same and act together.

Imagine you have a big box of identical marbles, each one is exactly like the others, and when they’re all together, they make something bigger, like a marble floor. A chemical substance is like that marble floor: it’s made up of many tiny pieces (called molecules) that are all the same, and they work as one.

Think about your favorite cookie, say, chocolate chip. All the cookies in a batch look similar because they’re made from the same ingredients: flour, sugar, butter, and chocolate chips. A chemical substance is like that whole batch of cookies, it's made up of many identical pieces (like all those cookies) that behave the same way.

But if you mix two kinds of cookies, say, chocolate chip and oatmeal, you get a new kind of snack. That’s like mixing chemical substances to make something different!