A group of two or more atoms that act like one atom is called a molecule.

Here's why:

* Atoms are the basic building blocks of matter.

* Molecules are formed when two or more atoms bond together chemically.

* The resulting molecule has its own unique properties, distinct from the individual atoms that make it up.

For example, two hydrogen atoms (H) can bond to form a molecule of water (H₂O). Water has completely different properties than either hydrogen or oxygen alone.