Position of Hydrogen in Periodic Table

Hydrogen is the first element of the periodic table. Hydrogen has the simplest atomic structure and consists of a nucleus containing one proton with a charge +1 and one orbital electron. The electronic structure is written as 1s¹.

Elements are place in the periodic table according to their outermost electronic configuration. So hydrogen may be placed with alkali metals. But, hydrogen attains noble gas configuration of helium atom by gaining one electron. It forms the hydride ion H^– (1s²) like halogens by gaining one electron.

On electrolysis of used alkali hydride, hydrogen is liberated at anode just as chlorine is liberated at anode during electrolysis of sodium chloride. Thus hydrogen ought to be placed in group 17 along with halogens.

Hydrogen also resembles group 14 elements, since both have a half filled shell of electrons.

So where should hydrogen be placed? This problem is solved by placing hydrogen neither with alkali metals nor with halogens. It has been given a unique position in the periodic table.