Position of Period 1 Elements in The Periodic Table
Although both hydrogen and helium are in the s-block, neither of them behaves similarly to other s-block elements. Their behaviour is so different from the other s-block elements that there is considerable disagreement over where these two elements should be placed in the periodic table.
Hydrogen is sometimes placed above lithium, above carbon, above fluorine, above both lithium and fluorine (appearing twice), or left floating above the other elements and not assigned to any group in the periodic table.
Helium is almost always placed above neon (which is in the p-block) in the periodic table as a noble gas, although it is occasionally placed above beryllium due to their similar electron configuration.
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