Gaseous diatomic hydrogen, or H2, was formally described for the first time by T. von Hohenheim (better known as Paracelsus, 1493-1541) who obtained it artificially by mixing metals with strong acids. Paracelsus was not aware that the flammable gas generated in these chemical reactions was composed of a new chemical element.
In 1671, Robert Boyle rediscovered and described the reaction that took place between iron filings and diluted acids, and that it generated hydrogen gas. However, the discovery of hydrogen in its pure form and the composition of water was made by Henry Cavendish in the year 1766.
Hydrogen is the simplest chemical element (formed only by a proton and an electron) and most abundant in the universe. It is found mainly in the form of hydrogen gas (H2) in stars and gaseous planets, and also appears attached to other elements forming a wide variety of chemical compounds, such as water (H2O) and most organic compounds.
It is a colorless, odorless and tasteless gas at room temperature. It is the lightest element that exists, being approximately 14 times less heavy than air. Its molecule consists of two hydrogen atoms (H2) joined by a covalent bond.
Chemically, it is able to combine with most of the elements when the conditions are right. It has great affinity with oxygen, with which it is cold combined very slowly, but in the presence of a flame or an electric spark it almost instantaneously explodes. Therefore, mixtures of hydrogen and air must be handled with great caution.
A very important property of this chemical element is its reducing power. In fact, at high temperatures the hydrogen reacts with some oxides reducing them. This reducing power, which is based on the tendency of this gas to oxidize in the oxidation state +1, also has application in many chemical processes.