Position of hydrogen, according to mendeleev’s periodic table.

Hydrogen has properties similar with halogens (group VII). That is, the molecular formula of hydrogen is H₂ while the molecular formulas of fluorine and chlorine are F2 and Cl2, respectively. Meanwhile, the chemical properties of hydrogen and alkali metals (group I) are similar, also a similarity is found in the molecular formulae of the compounds of hydrogen alkali metals (Na, K, etc) formed with chlorine and oxygen. From these observations, it is not possible to decide whether the correct position of hydrogen is in the group of alkali metals (group I) or in the group of halogens (group VII).