Question

A pure substance that is made of only one kind of atom is called _________.

Answer 1

Homogeneous is all one substance while Heterogeneous is just the opposite.

Answer 2

It depends how strictly you apply the idea of 'one kind' of atom.
A pure substance of one kind of atom would be called an element, or chemical element.
The atoms of a single element can occur in different forms, known as isotopes, but that is probably not what your question is asking about.