Hydrogen

1) Unique Position of Hydrogen

• Electronic configuration: 1s¹
• Shows resemblance with alkali metals and halogens
• Can lose or gain one electron
• Acts as electropositive, electronegative and amphoteric element
• Does not belong exclusively to any group

2) Occurrence of Hydrogen

• Most abundant element in the universe
• Major component of stars and sun
• Source of solar energy (nuclear fusion)
• ~0.9% by weight in Earth’s crust

3) Isotopes of Hydrogen

• Protium (¹H): 1 proton, no neutron (≈ 99.8%)
• Deuterium (²H or D): 1 proton, 1 neutron
• Tritium (³H or T): 1 proton, 2 neutrons (radioactive)

Note: Tritium emits β⁻ rays; half-life ≈ 12.4 years

4) Preparation of Hydrogen

(a) Electrolysis of Water

2H₂O → 2H₂ + O₂

(b) From Steam (Lane’s Process)

3Fe + 4H₂O → Fe₃O₄ + 4H₂

(c) From Water Gas (Bosch Process)

C + H₂O → CO + H₂

CO + H₂O → CO₂ + H₂

(d) From Hydrolith

CaH₂ + 2H₂O → Ca(OH)₂ + 2H₂

(e) From Acids

Zn + H₂SO₄ → ZnSO₄ + H₂

5) Physical Properties of Hydrogen

• Colourless, odourless, tasteless gas
• Lightest gas known
• Boiling point: 20.4 K
• Melting point: 13.8 K
• Density: 0.0899 g/cm³

6) Chemical Properties of Hydrogen

(a) Combustion

2H₂ + O₂ → 2H₂O

(b) With Non-metals

N₂ + 3H₂ → 2NH₃

S + H₂ → H₂S

(c) With Metals (Hydrides)

2Na + H₂ → 2NaH

(d) As Reducing Agent

Fe₃O₄ + 4H₂ → 3Fe + 4H₂O

(e) Hydrogenation

C₂H₄ + H₂ → C₂H₆

7) Forms of Hydrogen

• Ortho-hydrogen: Parallel nuclear spins
• Para-hydrogen: Opposite nuclear spins
• At room temperature: 75% ortho, 25% para

Other Forms:

• Nascent Hydrogen: Highly reactive, freshly generated
• Atomic Hydrogen: Produced in electric arc
• Occluded Hydrogen: Absorbed by metals like Pd, Pt

8) Uses of Hydrogen

• Manufacture of ammonia and methanol
• Hydrogenation of vegetable oils
• Oxy-hydrogen welding
• Rocket fuel