Types of Hydrogen

1.    Molecular Hydrogen (H₂)

↪ Molecular hydrogen is formed by the combination of two hydrogen atoms bonded together through a covalent bond (H-H). It is also called dihydrogen.

↪ Molecular hydrogen is formed when reactive metals displace hydrogen from dilute mineral adds and exists as gas at room temperature.

2.    Atomic Hydrogen [H]

↪ An atomic hydrogen is one which contains one proton at its nucleus and one and one electron in its K - shell. Due to this reason, it has strong desire to combine with another hydrogen by the sharing of electron resulting the formation of molecular hydrogen.
             

⁕ Preparation of atomic hydrogen
   

↪ Atomic hydrogen is prepared by passing a stream of hydrogen gas at atmospheric pressure through an electric arc struck between tungsten electrodes at about 2000-3OOO°C.



↪ Heat is produced when some of the hydrogen burns with oxygen.
↪ Atomic hydrogen is strong reducing agent. It is more powerful reducing agent that molecular and nascent hydrogen.

{Notes: LEO = Loss of electron is Oxidation and GER = Gain of electron is Reduction}


i. It reduces oxygen and carbon monoxide

ii. It reduces ethene to ethane.

iii. It reduces aqueous solution of H₂O₂, AgNON­₃, copper acetate.

iv. Metallic oxides and chlorides are reduced.

Uses: Atomic hydrogen is used as reducing agent and in welding the metals

3.    Nascent Hydrogen

↪ The term nascent is derived from the Latin word Nascor meaning newly born.

↪ So, a nascent hydrogen which is just formed by means of a chemical reaction. It is also regarded as the hydrogen formed in contact to the to be reduced.

↪ It is very short-lived species and it quickly reacts with each other to form molecular hydrogen.

↪ Nascent hydrogen is more powerful reducing agent than molecular hydrogen which can be proved by the following chemical reactions.

i. Reaction with acidified KMnO₄  

↪ When molecular hydrogen obtained by reacting zinc with dil. Sulphuric acid is passed through acidified solution of KMnO₄ then pink color of KMnO₄ remain unchanged.

↪ But Nascent hydrogen obtained by dropping a piece of zinc into acidified KMnO₄ discharge pink color of KMnO₄ due to the reduction caused by nascent hydrogen.

ii.  Reaction with acidified K₂Cr₂O₇
↪ Molecular hydrogen can’t change the orange color of acidified K₂Cr₂O₇.

↪ But nascent hydrogen obtained by dropping a piece of zinc into acidified K₂Cr₂O₇ turns the orange color of acidified K₂Cr₂O₇ into green due to reduction caused by nascent hydrogen.

iii. Reaction with acidified FeCl₃

↪ When molecular hydrogen is passed through acidified solution of ferric chloride then yellow color of FeCl₃ remained unchanged.

↪ But when a piece of Zn is dropped into acidified solution of FeCl₃ then yellow color of FeCl₃ turns green due to reduction of FeCl₃ into FeCl₂.

⁕ Relative Reactivity of Nascent Hydrogen

‏‏‎Nascent hydrogen is more powerful reducing agent over molecular hydrogen due to following reasons.

↪ Nascent hydrogen is more energetic as it is associated with the excess energy that is released during the formation of molecular hydrogen.

↪ As nascent hydrogen is just formed by means of chemical reaction it has high internal pressure so more reactive than molecular hydrogen.

⁕ Differences between Nascent and Atomic Hydrogen