In spite of their adjacency in the periodic table, the properties of halogens and nonmetals are very different. The halogens are among the most chemically reactive elements in the periodic table, exhibiting a diverse chemistry in terms of the large numbers of compounds they can form. On the other hand, noble gases are the least chemically reactive elements. In fact, before the 1960s, chemists referred to these elements as inert gases, because it was believed that they exhibited no chemistry whatsoever. It was discovered, however, that krypton and xenon are capable of bonding with other elements, principally fluorine. Compounds have not yet been formed from helium, neon, or argon.