Hydrogen (symbol H, atomic number 1) is the simplest, lightest, and most abundant chemical element in the universe. It plays a fundamental role in fundamental physics, astrophysics, chemistry, and engineering.
Contribution of Hydrogen to Vital Processes
Hydrogen, mainly in the form of H⁺ (protons) and bonded within organic molecules, plays a fundamental role in cellular bioenergetics. It is involved in the electron transport chain (Krebs cycle and oxidative phosphorylation), where proton gradients across mitochondrial membranes drive ATP synthesis. It also contributes to intracellular pH regulation and numerous enzymatic reactions (notably redox reactions). Consequence of a deficiency: An imbalance in H⁺ quickly disrupts energy metabolism, acid–base equilibrium, and protein stability, potentially leading to severe cellular failure or cell death.
History of Discovery
17th Century: First Observations Hydrogen gas was first observed by Théodore de Mayerne (1605) and then by Robert Boyle (1660), when they noticed that a metal reacting with an acid produced a flammable gas, without identifying it as a distinct element.
1766: Identification by Henry Cavendish Henry Cavendish isolated and studied this gas, which he named "inflammable air." He demonstrated that its combustion produced water, contradicting the idea that water was an element.
1783: Naming by Antoine Lavoisier Lavoisier established that water is a compound of two gases: hydrogen and oxygen. He gave the gas the name "hydrogen," from the Greek hydro (water) and genes (generate).
Atomic Structure
Constitution: One proton and one electron, no neutron for the most common isotope (¹H, protium). Isotopes:
Protium (¹H): 99.985% natural.
Deuterium (²H or D): one proton + one neutron, used in fusion reactors and isotopic labeling.
Tritium (³H or T): radioactive (T1/2 ~ 12.3 years), used in nuclear research, weaponry, and luminous signage.
Physical Properties
Diatomic gas (H2), colorless, odorless, very light.
Molar mass: ~ 2.016 g/mol
Melting point: 13.99 K (-259.16 °C)
Boiling point: 20.27 K (-252.88 °C)
Density: ~0.08988 g/L
Excellent thermal conductivity in the gaseous state.
Chemical Reactivity
Very reactive with halogens, oxygen (explosive), sulfur, alkali metals.
Forms hydrides with various elements.
Powerful reducing agent, used in catalytic hydrogenation.
Amphoteric: acts as an acid (H+) or base depending on the context.
Industrial and Technological Applications
Ammonia synthesis (Haber-Bosch process).
Petroleum refining: hydrodesulfurization.
Fuel cells: H2 → electricity + water (high efficiency).
Clean energy carrier (green hydrogen through electrolysis).
Used in cryogenics: fluid at very low temperatures.
Aerospace: fuel in cryogenic engines (H2 + O2).
Cosmological and Astrophysical Role
Primordial hydrogen from the Big Bang (~75% of baryonic mass).
Fuel for stars: H → He via pp cycle or CNO cycle.
Presence in the interstellar medium: H I, H2, H+.
21 cm line: fundamental tool of radio astronomy.
Fundamental Physical Issues
The hydrogen atom is a fundamental two-body system for testing quantum mechanics and QED.
Perfectly known spectrum (Lyman series, Balmer series…).
Allows probing of fundamental constants, symmetries, and cosmological hypotheses.
