A scientist who studies elements, atoms, and molecules is called a chemist.

Here's why:

* Chemistry is the branch of science that deals with the composition, structure, properties, and reactions of matter.

* Elements are the fundamental building blocks of matter.

* Atoms are the smallest unit of an element that retains the chemical properties of that element.

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

So, a chemist is the expert in the study of all these fundamental components of matter.