Justify the position of hydrogen in the periodic table on
the basis of its electronicconfiguration.
Hydrogen is the first element of the periodic table. Its
electronic configuration is
Due to the presence of only one electron in its 1s
shell, hydrogen exhibits a dual behaviour, i.e., it resembles
both alkali metals and halogens.
Resemblance with alkali
1. Like alkali metals, hydrogen contains one
valence electron in its valency shell.
H : 1s1
Li : [He]
Hence, it can lose one electron to form a
2. Like alkali metals, hydrogen combines with
electronegative elements to form oxides, halides, and
1. Both hydrogen and halogens require one
electron to complete their octets.
F : 1s2
Cl : 1s2
Hence, hydrogen can gain one electron to form
a uninegative ion.
2. Like halogens, it forms a diatomic molecule and several
Though hydrogen shows some similarity with both alkali
metals and halogens, it differs from them on some grounds. Unlike
alkali metals, hydrogen does not possess metallic
characteristics. On the other hand, it possesses a high
ionization enthalpy. Also, it is less reactive than
Owing to these reasons, hydrogen cannot be placed with
alkali metals (group I) or with halogens (group VII). In
addition, it was also established that
H+ ions cannot exist freely
as they are extremely small. H+
ions are always associated with other atoms or molecules.
Hence, hydrogen is best placed separately in the periodic
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