what is a pure chemical substance with its own characteristic, atomic structure, and chemical properties?

The answer is: Chemical element

Explanation:

A chemical element refers to the chemical substance or species containing a fixed number of neutrons and protons in its nuclei. The atomic number of an element is equal to the number of protons.

All the matter present in the universe is composed of these chemical elements. The chemical and physical properties of the these elements are summarized in periodic table.