Hydrogen

9.1. Hydrogen has electronic configuration 1s¹similar to the outer electronic configuration (ns¹) of alkali metals, which belong to the first group of the periodic table. On the other hand, like halogens (with ns²np⁵) configuration belonging to the seventeenth group of the periodic table, it is short by one electron to the corresponding noble gas configuration, helium (1s²). Hydrogen, therefore, has a resemblance to both alkali metals, which lose one electron to form unipositive ions, as well as with halogens, which gain one electron to form uni-negative ion. Like alkali metals, hydrogen forms oxides, halides and sulphides. However, unlike alkali metals, it has a very high ionization enthalpy and does not possess metallic characteristics under normal conditions. In terms of ionization enthalpy, hydrogen resembles more with halogens. Like halogens, it forms a diatomic molecule, combines with elements to form hydrides and a large number of covalent compounds. However, in terms of reactivity, it is very low as compared to halogens.