Hydrogen's dual behaviour is amazing is as follows :
Resemblance with alkali metals :
a. Electronic configuration :
The valence shell electron configuration of hydrogen and alkali metals are similar i.e. ns^1
b. Formation of unipositive ion :
Hydrogen as well as alkali metals lose one electron to form unipositive ions.
c. Formation of oxides , halides and sulphides :
Just like alkali metals hydrogen combines with electronegative elements such as oxygen , halogen and sulphur forming oxide , halide and sulphide respectively.
Example : Na2O NaCl Na2S H2O HCl H2S
d. Reducing character :
List , alkali metals hydrogen also acts as reducing agent.
CuO + H2 --^--> Cu + H2O
;
B2O3 + 6K ---^--> 3K2O + 2B
Resemblance with halogens :
a. Electron configuration : Both have one electron less than that of preceding inert gas configuration.
b. Atomicity : Like halogen, hydrogen forms diatomic molecule too. For example, Cl2, Br2, I2 etc.
c. Ionization enthalpy :
Hydrogen as well as halogens both have higher ionization enthalpies.
H 1312 kJ/mol
F 1680 kJ/mol
Cl 1255 kJ/mol
d. Formation of uninegative ion :
Both hydrogen as well as halogens have the tendency to gain one electron to form uninegative ion so as to have the nearest noble gas electronic cofiguration.
e. Formation of hydrides and covalent compounds.
Hydrogen as well as halogens combine with elements to form hydrides and a larger number of covalent compounds.
For example :
CCl SiCl4 CH4 NaCl SiH4 NaH
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