Hydrogen

           

           

Position Of Hydrogen In Periodic Tables:-

The position of Hydrogen in periodic table is yet unsolved problem. It is placed above IA (alkali metals). IVA (Carbon family) and VIIA (halogen family) due to resemblance at small extent. It does not resemble completely with the members of any these groups elemenrs. The different behaviour of hydrogen can be explaining the fact that, it contains only one electron in its shell and only one proton in the nucleus with absence of neutron.

Comparison With Alkali Metals:-

Similarities:- like alkali metals, hydrogen possessing one electron in 's' orbital i.e both belong to s-block in respect of electronic configuration, both are monovalent and in electrolysis, both are deposited on cathode.
Dissimilarities:- Hydrogen is a gas, non-metal, does not exist in H state like Na etc. It can exist only in solvent form as Hydronium ion.

Comparison With Carbon Family:-

Similarities:
Like carbon family hydrogen has half filled electronic configuration in valence shell and some thermodynamics properties are also similar as ionization potential and electron affinity. Both carbon and hydrogen have close association in organic compounds.
Dissimilarities:
Hydrogen is a gas monovalent, non-metal, having 's' orbital in valence shell while carbon family is tetra-valent exist in solid state and their valence shell possessing 's' and 'p' orbitals.

Comparison With Halogen Family:-

Similarities:
Like halogen family hydrogen is diatomic gas, monovalent and gaints one electron from metal and become hydride, both are non-metals.
Dissimilarities:
Hydrogen can not exist as H positive like halogens and its electron affinity is also much less than those of halogens.

Conclusion:

In the light of above facts, hydrogen does not completely suit with members of any one group. Its exact position still undecided.

Industrial Preparation oF Hydrogen:

 i)From Electrolysis oF Water:
 ‎When ekectric curreent pass through water  containing some electrolyte (acid , base and salt) water decomposes into hydrogen and oxygen gas on electrolysis , hydrogen gas collected at cathode.
 ‎2H2O -----> 2H2 + O2
 ‎ii) Steam and Hydrocrbon Process
 ‎This process is also called oxidation of methane.
 ‎A mixture of natural gas and steam on heating at 900 C in presence of nickel catalyst , produce a mixture of CO and H2 commanly known as "water gas" as
 ‎CH4 + H2O ---->[3H2 + CO]
 ‎iii) By The Action oF Steam On Coal(coke) :
 ‎When steam is passed over red hot coke at 1000C, water gas is formed. It is an oxidation reaction.
 ‎C + H2O ----> H2 + CO
 ‎Separation oF Hydrogen Gas From Water Gas:
 ‎Mathod 1:  When water gas is passed over red hot iron at 500C mixture of CO2 gas dissolve in water leaving behind free hydrogen gas.
CO + H2 + H2O ------> CO2 + 2H2

Method 2: When water gas is cooled at -200 celsius with liquid air, CO becomes liquid and free hydrogen gas is obtained. Traces of CO from contaminated hydrogen can be removed by passing it through NaOH, where CO is absorbed by NaOH and HCOONa is obtained.

CO + NaOH -----> HCOONa

iv) Steam With Methanol Process (Oxidation Of Methanol):
When the mixture of methyl alcohol (wood spirit) and steam is heated at 250 celsius, CO2 , H2 gas are formed as
CH2OH + H2O ----> CO2 + 3H2
Carbon dioxide gas is separated by passing the mixture through water under high pressure where, CO2 dissolved in water and free hydrogen gas is obtained.

v) Thermal Decomposition Of Hydrocarbon ( Pyrolysis Or Cracking):
Natural gas is heated at 700 celsius in the absence of oxygen; on decomposition carbon black and hydrogen gas are formed, carbon black is used as filler in tyres manufacturing, type writer carbon papers, dyes etc.
CH4 + C ----> C + 2H2

vi) Thermal Decomposition of Ammonia:
When liquid ammonia is heated at 1000 celsius in presence of catalyst, mixture of N2 and H2 gases are formed. When this mixture is cooled at -196 celsius, N2 gas becomes liquid leaving behind pure hydrogen gas as
2NH3 ----> N2 + 3H2.

Atomic Hydrogen: 

Definition Of Atomic Hydrogen:

Ordinary hydrogen exist in diatomic state, therefore , it is called as molecular hydrogen. ' The product obtained as a result of dissociation of molecular hydrogen is known as atomic hydrogen'. Hydrogen is found in the combined state in the form of compounds, the most abundant compound is water.

Preparation of Atomic Hydrogen:

In 1912, Langmuir prepared atomic hydrogen by thermal decomposition of ordinary hydrogen Or by electrical dissociation of molecular hydrogen under reduce pressure.
i) Atomic hydrogen is prepared by heating molecular hydrogen at 5000 celsius as:
H2 + 104 k.cal ----> 2 [H]
ii) Atomic hydrogen can also be prepared when electric current is passed through gas under reduce pressure i.e 1mmHg -to-0.1mmHg.
H2 ---> 2[H]
Properties of Atomic hydrogen:-
  Atomic hydrogen is much more reactive than molecular hydrogen. Expected reaction of molecular hydrogen are only those in which more than this energy will not takes place spontaneously. For the reaction of atomic hydrogen there is no such condition.

Uses Of Atomic Hydrogen:-

Atomic hydrogen is used to produce atomic hydrogen torch to attain a temperture of 4000 to 5000 celsius which employed in welding aluminium alloys, high chromium and nickel steels. It is based on the fact that when a jet of hydrogen is passed through an electric arc set up between tungsten rods.