Atomic hydrogen , Nascent hydrogen

Atomic Hydrogen

Langmuir ,in 1915, obtained atomic hydrogen by dissociating on a hot filament of tungsten or platinum. The dissociation of molecular hydrogen is an endothermic process.

The atomic hydrogen is stable only for a fraction of a second and immediately reverts back to its molecular form, liberating a large amount of energy.

Atomic hydrogen is extremely reactive, being more reactive than ordinary, nascent, or adsorbed oxygen. When it is passed over metals or non-metals, it forms hydrides at normal temperatures, excepting for nitrogen, to which it does not react.

Atomic hydrogen is an extremely powerful reducing agent, reducing oxides chlorides and sulphides of some metals like Ag, Hg, Cu etc. to metals at ordinary temperature.

Nascent Hydrogen

The hydrogen gas, which is just liberated as a result of a chemical is called nascent hydrogen or newly born hydrogen. It is obtained by passing dihydrogen gas at atmospheric pressure through an electric arc between two tungsten rods. The electric arc maintains a temperature around 4000 - 4500°C. As the molecules of dihydrogen gas pass through the electric arc, these absorb energy and get dissociated into atoms as nascent hydrogen. It is more reactive than ordinary hydrogen and its colour is not discharged. (pink in colour). For example, if ordinary hydrogen is passed through acidified KMnO₄ it does not get decolourised. However, if zinc pieces are added to the same solution, bubbles of hydrogen rise up through the solution and the colour is discharged due to the reduction of KMnO₄ by nascent hydrogen.