Hydrogen-1 (also known as protium) is the most common isotope of hydrogen. What is unusual about its structure is actually its *simplicity*:

* Single proton: It only consists of one proton in its nucleus. No neutrons are present.

* Single electron: It has only one electron orbiting the nucleus.

This makes hydrogen-1 the simplest atom in the universe. Its simplicity is what makes it so abundant and chemically reactive.

Let me know if you'd like to delve into more details about hydrogen isotopes or their properties!