Although hydrogen is normally listed at the top of Group I, the alkaline metals, on the periodic table, there is much debate as to which group it should belong. Many chemists believe hydrogen doesn't belong in any group and that Group I begins with lithium.
In addition, some chemists believe hydrogen should belong with the alkali metals in Group I, while others put it in Group VIIIA with the noble gases, such as helium, neon, argon, krypton and xenon.
Recent research has shown a close link between hydrogen and the alkaline metals, according to the Royal Society of Chemists. Not only does hydrogen take on the properties of a metal under high pressure, but new evidence shows that it can replace the other alkali metals in a variety of compounds.