Hydrogen is the only element that does not contain any neutrons in its nucleus. Hydrogen is comprised of one proton and one electron. It is a diatomic molecule, which means that it typically exists as two hydrogen atoms joined together.
Hydrogen is the simplest element on the periodic table and the most abundant element in the universe. One of the best-known properties of hydrogen is its ability to combine with oxygen to form water. This feature gives the element its name. Hydrogen is derived from the Greek "hydro" and "genes," which means "forming water." While hydrogen's existence was known for centuries, it was first recognized as an element in 1766 by Henry Cavendish.