hydrogen

Hydrogen shares with helium an electronic configuration 1s. As earlier versions of the periodic table placed helium as the first member of the noble, or inert, gases, so was hydrogen placed as the first member of the alkali metals, above lithium (2s). Periodic tables continue to place helium above the noble gases, a family of which it is clearly a member, rather than place it above beryllium (also 2s, because helium shares no properties with the alkali metals. Hydrogen is, however, a unique element that fits into no chemical family. Many contemporary versions of the periodic table continue to place the element above lithium, but hydrogen is not at all a metal like lithium. It does however, exist in metallic form (under extremely high pressures) and can, at least in theory, exhibit the properties of a metal. Some newer periodic tables place hydrogen in the center by itself, unattached to any other group (some treat helium in a similar manner, grouping the two as a separate 1s block); others place it above fluorine, although the element shares only a few properties with the halogen gases. Still other tables double the element, placing it above both lithium and fluorine. The Periodic Spiral places hydrogen at the center of three families: group 18 (the noble gases); group 1 (the alkali metals) and group 17 (the halogens). This placement maintains hydrogenís unique status while acknowledging the commonalties between hydrogen and the elements of these three groups. Hydrogen, at least in some instances, should be classified with the halogens (which form X - ions), just as its tendency to form H+ likens it to the alkali metals (which form M+ ions). Hydrogen is a gas, like the halogen and inert gases; a metal, like lithium and its group 1 siblings; and very reactive, like both fluorine and lithium.