Hydrogen - Position of Hydrogen in Periodic Table

Hydrogen is the first element in the periodic table with the electronic configuration $1s^1$.

It exhibits a dual nature, showing similarities to both Alkali Metals (Group 1) and Halogens (Group 17).

Resemblance with Alkali Metals: Like $Li$, $Na$, and $K$, Hydrogen has one electron in its outermost shell and can form a unipositive ion $H^+$.

Resemblance with Halogens: Like $F$, $Cl$, and $Br$, Hydrogen is one electron short of the nearest noble gas configuration ($He$) and can form a uninegative ion $H^-$.

Diatomic Nature: Hydrogen exists as a diatomic molecule $H_2$, similar to halogens like $Cl_2$.

Anomalous Nature of $H^+$: The loss of an electron from a hydrogen atom results in a nucleus (proton) of extremely small size (approx $1.5 \times 10^{-3} \text{ pm}$), which does not exist freely and associates with water to form $H_3O^+$.

Ionization Enthalpy: The ionization enthalpy of Hydrogen ($1312 \text{ kJ mol}^{-1}$) is much higher than that of alkali metals and is comparable to halogens (e.g., Fluorine is $1681 \text{ kJ mol}^{-1}$).