Hydrogen

Chemical element; atomic number 1 (one proton within the atomic nucleus).

The three natural isotopes are shown above; ³H (tritium, marked in red colour) is unstable (radioactive). Under natural conditions, it is present only in trace amounts; the isotope ²H (deuterium) makes up a very small percentage (0,015 %) of hydrogen as well.

According to the periodic system, hydrogen belongs to the group of alkali metals. Because of its very small electronic sheath, however, hydrogen is clearly different from the true alkali metals. Nevertheless, the element reacts with many reaction partners by transfering one (its only) electron, in a similar way as alkali metals do. Elemental hydrogen exists as gaseous H₂ (a molecule made of two hydrogen atoms). Hydrogen is reacting in a violent way with oxygen leading to the formation of water (H₂O).