Hydrogen
1.0 Basic Information
2.0 Atomic and Physical Properties of Hydrogen (reference: NCERT)
3.0 Dihydrogen
4.0 Physical Properties
5.0 Chemical Properties
6.0 Uses of Dihydrogen
7.0 Compounds of Hydrogen
8.0 Hard and Soft Water
9.0 Hydrogen Peroxide
10.0 Volume strength of Hydrogen Peroxide
1.1 Unique Position of Hydrogen in the Periodic table
Based on the electronic structure $(1s^1)$, hydrogen should be placed in alkali metal group. Some of its properties also resemble that of alkali metals. It form $H^+$ ion like alkali metals. In some way the electronic structure of hydrogen also matches with that of halogens.
Like halogens in some reactions it also gains electron and form negative ion. Like alkali metals, hydrogen forms oxides, halides and sulphides. However, unlike alkali metals, it has a very high ionization enthalpy and does not possess metallic characteristics under normal conditions.
In fact, in terms of ionization enthalpy, hydrogen resembles more with halogens, ${\Delta _i}H$ of $Li$ is $520\ kJmol^{–1}$, $F$ is $1680\ kJ mol^{–1}$ and that of $H$ is $1312\ kJ mol^{–1}$.
Like halogens, it forms a diatomic molecule, combines with elements to form hydrides and a large number of covalent compounds. However, in terms of reactivity, it is very low as compared to halogens.
As all the properties of hydrogen cannot be correlated with any of the groups in the periodic table. Therefore it is better to treat hydrogen as a group on its own.
