| Property | Value |
|---|---|
| Element Symbol | H |
| Atomic Number | 1 |
| Atomic Mass | 1.008 u |
| Classification | Nonmetal |
| Physical State | Gas (at STP) |
| Group | 1 (I A) |
| Period | 1 |
| Block | s-block |
| Property | Value |
|---|---|
| Melting Point | -259.14ยฐC |
| Boiling Point | -252.87ยฐC |
| Density | 0.00009 g/cmยณ |
| Color | Colorless |
| Electron Config | 1sยน |
| Protons / Electrons | 1 / 1 |
| Neutrons (Protium) | 0 |
Hydrogen is the first and lightest element in the periodic table โ the simplest atom in the universe consisting of just one proton and one electron. It comprises approximately 75% of all visible matter in the universe and is the fuel of stars. On Earth it is most commonly found combined in water (HโO) and organic compounds.
Henry Cavendish (1731โ1810): English scientist who produced hydrogen by reacting metals with acids and demonstrated its unique properties. He called it "inflammable air."
Antoine Lavoisier (1743โ1794): French chemist who named hydrogen from the Greek words "hydro" (water) and "genes" (born of), after demonstrating that water is formed when hydrogen burns in oxygen.
The name "hydrogen" derives from Greek: hydro (water) + genes (forming). Lavoisier coined this name in 1783 after confirming that burning hydrogen produces water, revealing the elemental composition of HโO for the first time.
| Method | Share |
|---|---|
| Steam Methane Reforming | 48% |
| Oil Reforming | 30% |
| Coal Gasification | 18% |
| Water Electrolysis | 4% |
Hydrogen is the most fundamental building block of the cosmos. Every star โ including our Sun โ generates energy through hydrogen fusion. On Earth, the shift to a hydrogen economy represents our most promising path to carbon-neutral energy. Green hydrogen produced from renewable electricity is the "fuel of the future" that could decarbonize heavy industry, shipping, and aviation.
The German airship LZ 129 Hindenburg, filled with 200,000 mยณ of hydrogen, caught fire during landing in New Jersey. The disaster killed 36 people and ended the era of hydrogen airships. Ironically, modern research suggests the outer fabric coating was more flammable than the hydrogen itself.
In 1939, Hans Bethe described the proton-proton chain reaction that powers the Sun โ four hydrogen nuclei fuse to form one helium nucleus, releasing enormous energy (E=mcยฒ). This earned Bethe the 1967 Nobel Prize and explained why stars shine for billions of years.
The global hydrogen economy is projected to reach $2.5 trillion by 2050. Green hydrogen โ produced from renewable energy โ will be critical to decarbonize sectors that cannot be electrified directly: steel, cement, aviation, shipping, and long-haul trucking.
| Property | Value |
|---|---|
| Standard State | Diatomic gas (Hโ) |
| Melting Point | -259.14ยฐC (13.99 K) |
| Boiling Point | -252.87ยฐC (20.28 K) |
| Critical Temperature | -240.17ยฐC (33.0 K) |
| Critical Pressure | 12.96 atm |
| Triple Point | 13.8 K at 0.07 atm |
| Property | Value |
|---|---|
| Density | 0.0899 kg/mยณ |
| Molar Volume | 22.4 L/mol |
| Speed of Sound | 1270 m/s |
| Thermal Conductivity | 0.1805 W/mยทK |
| Viscosity | 8.9 ร 10โปโถ Paยทs |
Hydrogen has the highest thermal conductivity of any gas (0.1805 W/mยทK), approximately 7ร higher than air. This makes it an excellent heat transfer medium used in power plant generators and industrial cooling systems. Liquid hydrogen is also used as a cryogenic coolant.
| State | Conductivity |
|---|---|
| Hโ Gas (normal) | Insulator / Non-conductor |
| Plasma State | Excellent conductor |
| Metallic H (Jupiter) | Metallic conductor |
| Ionized Hโบ (acid) | Proton conductor in solution |
Proton Exchange Membrane: In PEM fuel cells, Hโ is split into Hโบ protons and eโป electrons. Protons migrate through a membrane while electrons flow through an external circuit, generating electricity โ hydrogen acting as an indirect conductor.
Electrode Reaction: Anode: Hโ โ 2Hโบ + 2eโป | Cathode: ยฝOโ + 2Hโบ + 2eโป โ HโO
Molecular hydrogen (Hโ) in its ground state is diamagnetic โ it is weakly repelled by magnetic fields. This is because both electrons in Hโ are spin-paired. However, atomic hydrogen (Hโข) and ortho-hydrogen have paramagnetic properties due to unpaired electron spin states. The nuclear spin of hydrogen (spin-ยฝ) forms the basis of ยนH NMR spectroscopy.
Hydrogen gas has a magnetic permeability very close to vacuum (ฮผแตฃ โ 1.000000236 at STP). It has negligible magnetic influence in engineering applications. Its paramagnetic susceptibility is +2.1 ร 10โปโถ cmยณ/mol โ one of the lowest among all gases.
As a non-conducting gas, hydrogen does not experience Joule (resistive) heating in normal state. However, in hydrogen plasma systems used in semiconductor manufacturing and fusion research, electrical energy heats the hydrogen plasma via resistive mechanisms. Hydrogen-cooled generators use Hโ's thermal conductivity to remove Joule heat from generator windings.
Hydrogen's theoretical energy density as an electrochemical storage medium is 33.3 kWh/kg (LHV) โ the highest of any fuel. In flow batteries and regenerative fuel cells, hydrogen serves as an energy carrier. The hydrogen economy treats Hโ as a "battery" that stores energy chemically rather than electrically.
Hydrogen has just one proton and one electron (1sยน). Its electron distribution is the reference point for all quantum mechanics โ the Schrรถdinger equation is solved exactly for hydrogen, providing the basis for understanding all atomic orbitals.
| Property | Value |
|---|---|
| Standard Electrode Potential | 0.00 V (reference SHE) |
| Ionization Energy | 13.598 eV |
| Electron Affinity | 0.754 eV |
| Electronegativity | 2.20 (Pauling) |
| Fuel Cell OCV | 1.23 V (theoretical) |
| Property | Value |
|---|---|
| Flammability Range | 4โ75% in air |
| Autoignition Temp | 500ยฐC |
| NFPA Flammability Rating | 4 (Extreme) |
| NFPA Health Rating | 0 (Non-toxic) |
| Asphyxiation Risk | Yes (displaces oxygen) |