Page 2 - Microsoft Word - Lesson note-HYDROGEN

Difference from alkali metals:

 Hydrogen is diatomic, alkali metals are monoatomic.

 The ionization enthalpy of hydrogen is very high while that of alkali
metals is less.

 Hydrogen is non-metal while alkali metals are typical metals.

 The compounds of hydrogen are covalent while compounds of alkali
metals are ionic. For example: HCl is covalent, NaCl is ionic.

 The oxides of hydrogen are neutral. Oxides of alkali metals are basic

Resemblance with halogens:

 Electronic configuration: both contain one electron less than the
nearest noble gas configuration.

Difference from halogens:
 Water has less tendency for hydride formation. Halogens from halide
ions very easily.

 Unshared pairs of electrons are absent.

 Hydrogen oxide is neutral but oxides of halogens are acidic.

In the elemental form Hydrogen exists as a diatomic molecule H2 and is called
dihydrogen.

Production of dihydrogen

 The process of producing ‘syngas’ from coal is called ‘coal gasification.’
 Water gas is the name given to the mixture of carbon monoxide and
hydrogen. Water gas is also known as synthesis gas or syngas.

 The production of dihydrogen can be increased by reacting carbon
monoxide of syngas mixtures with steam in the presence of iron
chromate as catalyst. This reaction is called as water gas shift reaction.

The H–H bond dissociation enthalpy of dihydrogen (435.88 kJ mol ) is the
−1
highest for a single bond between two atoms of any elements. This property is
made use of in the atomic hydrogen torch which generates a temperature of
~4000K and is ideal for welding of high melting metals.
Though dihydrogen is rather inactive at room temperature because of very
high negative dissociation enthalpy, it combines with almost all the elements
under appropriate conditions to form hydrides.