Hydrogen


It's not easy to place hydrogen in the Periodic Table since it does not fit in any of the existing groups. Sometimes it is placed in the top of the group I (alkali metals) due to its relatively electropositive nature. On the other hand, it is not dificult to realize that its behaviour resembles that of halogens, accepting a second electron and becoming a mononegative ion.

In fact, the atomic structure of hydrogen (a nucleus with positive unitary electric charge and a single electron) is quite different from that of any other element, justifying its special place at the Periodic Table, not associated with any particular group.