The atomic number of an element is the number of protons in its nucleus. The first element on the periodic table is hydrogen, with an atomic number of one. Hydrogen (H1) is the lightest element and it plays a very important role in many chemical reactions.
Hydrogen atoms are very small and they have a single proton in their nucleus. This makes them very stable and unlikely to undergo nuclear fission or fusion. Hydrogen is also non-reactive, meaning it does not readily combine with other elements to form compounds. These properties make hydrogen a key ingredient in many industrial processes, such as oil refining and water treatment.
While hydrogen is an extremely important element, it can also be dangerous if mishandled. For example, when used in fuel cells to generate electricity, pure hydrogen can explode if it leaks out of containment.