The smallest atom in the periodic table in terms of mass is hydrogen, which has only one proton and one electron. Hydrogen has no neutrons. The element has an atomic number of 1 and atomic weight of 1.00794, making it the smallest of all the elements.
Henry Cavendish first recognized hydrogen as its own element in 1766. It takes its name from the Greek words "hydros" and "genes," which mean "water forming."
Hydrogen is the most abundant element in the universe. It is the main component of the atmospheres of several planets. The sun relies on hydrogen as a source of its energy production. On Earth, hydrogen forms many important compounds, including water (h2O,) hydrochloric acid (HCl) and ammonia (NH3.)