Hydrogen

Hydrogen is the simplest and lightest element — one proton, one electron — and by far the most abundant substance in the universe, making up most of the mass of stars and gas giant planets. On Earth it's rarely found alone; it's almost always locked up in compounds, above all water.

Group · Period: 1 · 1
At room temp: gas
Melts at: 13.81 K
Density: 0.00008988 g/cm³
Discovered: 1766

Uses

Hydrogen’s biggest single use today is industrial: the Haber-Bosch process combines it with nitrogen from the air to make ammonia, the backbone of synthetic fertilizer that feeds a large share of the world’s population. Oil refineries use huge volumes of it to remove sulfur from fuels and to break heavier crude fractions into lighter, more useful ones. It’s also the propellant of choice for high-performance rocket engines — burned with liquid oxygen, it was the fuel that powered the Space Shuttle’s main engines and still powers upper stages on several launch vehicles today.

More recently, hydrogen has become a serious candidate as a clean energy carrier: fuel cells combine it with oxygen to generate electricity with only water as a byproduct, an approach already used in some buses, trucks and forklifts. Whether that scales up depends heavily on how the hydrogen itself is produced — splitting water with renewable electricity is clean, but most hydrogen made today still comes from natural gas.

History

Hydrogen gas had been produced accidentally by chemists for centuries — reacting acids with metals reliably makes it — but it wasn’t recognized as a distinct substance until 1766, when English scientist Henry Cavendish identified “inflammable air” as a specific gas and carefully measured its properties. A few years later, Antoine Lavoisier repeated and extended Cavendish’s experiments, showed that burning this gas produced water, and gave it the name hydrogen — from the Greek for “water-forming.” That discovery played a key role in overturning the old phlogiston theory of combustion and establishing modern chemistry.

Fun facts

Hydrogen makes up roughly 75% of the normal matter in the universe by mass — more than every other element combined.
Liquid hydrogen has to be kept below −253°C, just 20 degrees above absolute zero, which is why it's stored and shipped as a cryogenic liquid.
The Sun converts about 600 million tonnes of hydrogen into helium every second through nuclear fusion — the reaction that powers essentially all life on Earth via sunlight.

Frequently asked questions

Is hydrogen a metal or a nonmetal?

Chemically, hydrogen behaves as a nonmetal under everyday conditions — it forms molecular gas (H2) and covalent compounds rather than a metallic lattice. Under extreme pressure, such as inside gas giant planets, it's thought to become metallic hydrogen, but that form doesn't exist naturally on Earth.

Why is hydrogen placed above lithium if it doesn't behave like an alkali metal?

It's a placement of convenience: hydrogen has one electron in its outer shell, the same as the alkali metals below it, so it's conventionally drawn at the top of group 1. But its chemistry is really its own — it can also gain an electron to form H⁻, something no alkali metal does.

Is hydrogen gas flammable or explosive?

Yes — hydrogen burns readily in air and, mixed with oxygen across a wide concentration range, can ignite explosively. That reactivity is exactly why it releases so much energy per kilogram as a fuel, and why hydrogen storage and handling is engineered so carefully.

Compounds

44 notable compounds containing H

Al(OH)3base
Aluminum hydroxide
An amphoteric compound able to react as either an acid or a base, typically forming a gelatinous precipitate when made in water.
Used for: Antacid medication, flame retardant, water treatment
NH3gas
Ammonia
A pyramidal molecule with a sharp, pungent odor; nitrogen's lone electron pair makes it a weak base that readily accepts a proton in water.
Used for: Fertilizer production, household cleaners, industrial refrigerant
(NH4)6Mo7O24salt
Ammonium heptamolybdate
A white, water-soluble salt that is the most common commercial form of molybdenum, widely used as an analytical reagent and micronutrient fertilizer.
Used for: Micronutrient fertilizer and reagent for detecting phosphate in analytical chemistry
NH4VO3salt
Ammonium metavanadate
A pale yellow-white crystalline salt that is the standard commercial starting material for manufacturing other vanadium compounds, since it decomposes cleanly to vanadium oxides on heating.
Used for: Industrial precursor for vanadium pentoxide and vanadium catalysts
NH4ReO4industrial
Ammonium perrhenate
A white, water-soluble crystalline salt that is the main commercial form in which rhenium is sold and shipped, since it is easily purified from ore-processing streams.
Used for: Primary industrial source material for producing rhenium metal and its alloys
AsH3gas
Arsine
A colorless, extremely toxic gas with a faint garlic-like odor, forming a pyramidal molecule much like ammonia. It decomposes on heated surfaces to deposit elemental arsenic, a reaction once used to detect arsenic poisoning.
Used for: Dopant source gas for gallium arsenide semiconductor manufacturing
Ba(OH)2base
Barium hydroxide
A strong alkaline base, sometimes called baryta, used in analytical chemistry to titrate weak acids because its solutions stay clear of carbonate interference.
Used for: Standard base for titrating weak organic acids in analytical chemistry
C7H5BiO4pharmaceutical
Bismuth subsalicylate
A pale yellow, water-insoluble organobismuth compound that coats and soothes the stomach lining while its salicylate portion provides mild anti-inflammatory action.
Used for: Active ingredient in over-the-counter upset-stomach remedies like Pepto-Bismol
Na2B4O7·10H2Omineral
Borax
A hydrated sodium borate mineral built from linked boron-oxygen rings, crystallizing naturally as soft, colorless crystals in dry lakebeds.
Used for: Laundry booster, metalworking flux, glass and ceramic glazes
H3BO3acid
Boric acid
A weak acid made of flat, triangular molecules that stack together through hydrogen bonding into soft, flaky white crystals.
Used for: Antiseptic, insecticide, eye-wash solutions, glass manufacturing
(NH4)2Ce(NO3)6reagent
Ceric ammonium nitrate
An orange-red crystalline salt and one of chemistry's most reliable single-electron oxidants, widely known simply as CAN in organic synthesis labs.
Used for: Oxidizing reagent in organic synthesis and printed-circuit etching
CsOHbase
Cesium hydroxide
The strongest of the common alkali metal hydroxides, a highly corrosive, deliquescent solid that dissolves readily in water.
Used for: Strong base used in specialty batteries and research chemistry
HAuCl4acid
Chloroauric acid
A yellow-orange, highly water-soluble acid formed when gold dissolves in aqua regia, serving as the standard source of dissolved gold for chemical and electrochemical work.
Used for: Starting material for gold electroplating and nanoparticle synthesis
CHCl3organic
Chloroform
A dense, sweet-smelling liquid in which three of methane's hydrogens are replaced by chlorine atoms. It was historically used as a surgical anesthetic before its toxicity was well understood.
Used for: Industrial solvent and precursor in refrigerant manufacturing
H2PtCl6acid
Chloroplatinic acid
A reddish-brown, highly water-soluble acid containing the hexachloroplatinate anion, typically handled as a hydrate and used as the entry point into most platinum chemistry.
Used for: Catalyst precursor in silicone curing and metal plating
PtCl2(NH3)2pharmaceutical
Cisplatin
A square-planar platinum(II) complex bearing two ammonia and two chloride ligands arranged on the same side of the molecule, a geometry that is essential to how it binds and disrupts DNA.
Used for: Widely used chemotherapy drug for treating various cancers
C2H6Oorganic
Ethanol
A simple alcohol whose polar hydroxyl group lets it mix freely with water while its hydrocarbon chain keeps it flammable and volatile.
Used for: Alcoholic beverages, fuel additive, disinfectant and solvent
GeH4gas
Germane
A colorless, flammable gas with a tetrahedral molecule much like methane, but far less stable and prone to decomposing into germanium metal and hydrogen. It's produced synthetically rather than found in nature.
Used for: Source gas for doping semiconductors by chemical vapor deposition
C6H12O6organic
Glucose
A six-carbon simple sugar that exists mainly as a ring-shaped molecule in solution, and the primary energy source for most living cells.
Used for: Cellular energy metabolism, IV fluids, food and beverage sweetening
HBracid
Hydrobromic acid
A strong acid formed by dissolving hydrogen bromide gas in water, comparable in strength to hydrochloric acid but a stronger reducing agent.
Used for: Manufacturing bromide salts and catalyst in organic synthesis
HClacid
Hydrochloric acid
A strong acid formed by dissolving hydrogen chloride gas in water, which fully ionizes into H⁺ and Cl⁻ ions in solution. It's also the main component of gastric acid in the human stomach.
Used for: Industrial metal cleaning (pickling), food processing, digestion in the stomach
HFacid
Hydrofluoric acid
A weak acid in water despite fluorine's high reactivity, yet uniquely able to dissolve glass by breaking apart silicon-oxygen bonds.
Used for: Glass etching, semiconductor manufacturing, metal cleaning
H2O2oxide
Hydrogen peroxide
A molecule built around an unstable oxygen-oxygen single bond, making it a strong oxidizer that slowly decomposes into water and oxygen gas.
Used for: Antiseptic and disinfectant, hair bleaching, rocket oxidizer
H2Segas
Hydrogen selenide
A colorless, extremely toxic gas with a foul odor reminiscent of rotten radishes, the selenium analog of hydrogen sulfide and a byproduct of some metal refining processes.
Used for: Dopant source gas in semiconductor and solar-cell manufacturing
H2Sgas
Hydrogen sulfide
A bent molecule best known for its rotten-egg smell, toxic at meaningful concentrations and commonly produced by decaying organic matter.
Used for: Industrial sulfur and sulfuric acid production, analytical reagent
LiOHbase
Lithium hydroxide
A strong alkaline compound that absorbs carbon dioxide efficiently for its weight, and a key precursor in manufacturing lithium-ion battery cathodes.
Used for: CO2 scrubbing in submarines and spacecraft, battery material production
Mg(OH)2base
Magnesium hydroxide
A weak, poorly soluble base that forms a milky suspension in water, giving rise to its common name.
Used for: Antacid and laxative (milk of magnesia), flame retardant filler
Cu2CO3(OH)2mineral
Malachite
A bright green basic copper carbonate mineral that forms naturally where copper ores weather, and is the same compound responsible for the green patina that develops on aged copper and bronze.
Used for: Ornamental stone and green pigment; ore of copper
CH4organic
Methane
The simplest hydrocarbon, a tetrahedral molecule of one carbon bonded to four hydrogens, and the main component of natural gas.
Used for: Natural gas fuel for heating and electricity generation
CH3Brorganic
Methyl bromide (bromomethane)
A colorless, odorless gas once widely used as an agricultural fumigant, now heavily restricted because it depletes stratospheric ozone.
Used for: Soil and commodity fumigant, largely phased out under the Montreal Protocol
Ni(OH)2industrial
Nickel(II) hydroxide
A pale green solid that acts as the active positive-electrode material in several rechargeable battery chemistries, cycling between nickel(II) and nickel(III) states as the battery charges and discharges.
Used for: Positive electrode material in nickel-cadmium and nickel-metal hydride batteries
HNO3acid
Nitric acid
A strong, highly corrosive oxidizing acid that slowly decomposes in light, turning older samples faintly yellow.
Used for: Fertilizer and explosives manufacturing, metal etching
Pd(OAc)2reagent
Palladium(II) acetate
An orange-brown, soluble palladium salt that is one of the most widely used catalysts in modern organic chemistry, central to many carbon-carbon bond-forming reactions.
Used for: Catalyst for Heck, Suzuki, and other palladium-catalyzed cross-coupling reactions
H3PO4acid
Phosphoric acid
A triprotic acid built around a central phosphorus atom bonded to four oxygens, moderately strong and notably non-volatile.
Used for: Soft drink acidity/flavoring, fertilizer production, rust removal
(C2H3Cl)norganic
Polyvinyl chloride
A synthetic polymer built from repeating vinyl chloride units, valued for being durable, lightweight, and resistant to weathering. It's one of the most widely produced plastics in the world.
Used for: Plumbing pipes, window frames, cable insulation, flooring
KOHbase
Potassium hydroxide
A strong, highly caustic alkali that dissolves readily in water and absorbs moisture from air. It's the potassium counterpart to sodium hydroxide (lye).
Used for: Manufacturing liquid soaps, batteries, and biodiesel
RbOHbase
Rubidium hydroxide
A strongly corrosive, highly water-soluble alkali hydroxide, among the strongest bases known due to rubidium's large, weakly polarizing cation.
Used for: Electrolyte component in some specialty batteries
H2SeO3acid
Selenous acid
A weak, water-soluble acid formed when selenium dioxide dissolves in water, serving as the parent compound for selenite salts.
Used for: Precursor for selenite compounds and a bluing agent in gun-metal finishing
NaHCO3salt
Sodium bicarbonate
A mildly alkaline ionic salt known as baking soda, which releases carbon dioxide gas when it reacts with acids or heat.
Used for: Baking leavening agent, antacid, fire extinguisher and cleaning agent
NaOHbase
Sodium hydroxide
A strong ionic base known as lye or caustic soda, highly corrosive and extremely soluble in water.
Used for: Soap and paper manufacturing, drain cleaner, industrial pH control
H2SO4acid
Sulfuric acid
A dense, strong diprotic acid and one of the most heavily produced industrial chemicals in the world, notable for its powerful dehydrating ability.
Used for: Car batteries, fertilizer manufacturing, industrial chemical processing
[Pd(NH3)4]Cl2salt
Tetraamminepalladium(II) chloride
A water-soluble coordination compound in which four ammonia molecules surround a central palladium ion, used as a convenient palladium source for plating baths.
Used for: Palladium source in electroless and electrolytic plating solutions
H2Ooxide
Water
A bent covalent molecule held together by polar O–H bonds, whose extensive hydrogen bonding gives it an unusually high boiling point and makes it the near-universal solvent for life and chemistry.
Used for: Universal solvent, drinking water, biological and industrial processes
RhCl(PPh3)3reagent
Wilkinson's catalyst
A landmark rhodium complex bearing three triphenylphosphine ligands that catalyzes the hydrogenation of alkenes under mild conditions, a discovery that helped found modern homogeneous catalysis.
Used for: Homogeneous catalyst for hydrogenating alkenes in organic synthesis

Isotopes

7 known isotopes

Swipe to see all columns →

Isotope	Natural abundance	Half-life	Decay mode	Mass excess	Binding energy / nucleon	Decay width
H-1 stable	99.9855%	Stable	—	7,288.97 keV	0 keV	—
H-2 stable	0.0145%	Stable	—	13,135.72 keV	1,112.28 keV	—

Show all 7 isotopes

H-3	—	12.32 Y	Beta-minus decay (100%)	14,949.81 keV	2,827.27 keV	1.17 × 10-24 eV
H-4	—	—	Neutron emission (100%)	24,621.13 keV	1,720.45 keV	—
H-5	—	5.3 MeV	Two-neutron emission (100%)	32,892.45 keV	1,336.36 keV	5.30 × 106 eV
H-6	—	1.55 MeV	Unknown	41,875.73 keV	961.64 keV	1.55 × 106 eV
H-7	—	0.09 MeV	Unknown	49,135 keV	940 keV	9.00 × 104 eV