Here's why:

* Everything is made of atoms: All matter, including rubber bands, is made up of tiny particles called atoms.

* Atoms form molecules: These atoms bond together to form molecules. In rubber bands, the primary molecule is polyisoprene, a long chain of carbon and hydrogen atoms.

* Polymers: Polyisoprene is a type of polymer, a large molecule made of many repeating smaller units. This long chain structure is what gives rubber its elasticity.

So, when you stretch a rubber band, you're actually stretching the long chains of polyisoprene molecules. The molecules themselves are not changing, but their arrangement within the rubber band is being altered.