Dihydrogen

Athanor · official

H₂ · 2.016 g/mol

IUPAC name: molecular hydrogen

Also called hydrogen, molecular hydrogen

Inorganic

Open in Athanor

Drawn from its SMILES with RDKit

DangerExtremely flammable gas

Names and identifiers

IUPAC name: molecular hydrogen
Synonyms: hydrogen, molecular hydrogen, Hydrogen
+ 37 more
Molecular hydrogen, Protium, hydrogen-1, DTXSID9029643, 7YNJ3PO35Z, CHEBI:18276, Hydrogen atoms, RefChem:389053, DTXCID00196437, 215-605-7, H, Atomic hydrogen, Hydrogen gas, H2, Hydrogen in Steel, 1g/piece, 1-Butanol, titanium(4+) salt, monohydrate, homopolymer (9CI), Hydrogen, atomic, H in Stainless Steel, 1g Balls of O 6.35 mm, hidrogeno, hydrogene, Wasserstoff, o-Hydrogen, p-Hydrogen, hydrogen molecule, monoatomic hydrogen, 1H, HYDROGEN [HSDB], HYDROGEN [MI], T101 Monoclonal Antibody, HYDROGEN [WHO-DD], Hydrogen in stainless steel, Hydrogen, >=99.99%, Hydrogen, >=99.999%, SCHEMBL29349524, SCHEMBL29357126, CHEBI:18140, CHEBI:33251
Molecular formula: H₂
Empirical formula: H
Molecular weight: 2.016 g/mol
Exact mass: 2.01565
CAS number: 1333-74-0
PubChem CID: 783
Canonical SMILES: [HH]
Isomeric SMILES: [HH]
InChI: InChI=1S/H2/h1H
InChIKey: UFHFLCQGNIYNRP-UHFFFAOYSA-N
Molfile

Names, InChI and the identifiers from PubChem, retrieved 2026-10-14.

Physical properties

TemperaturePressureDensity

Appearance: Hydrogen is a colorless, odorless gas. It is easily ignited. Once ignited it burns with a pale blue, almost invisible flame. The vapors are lighter than air. It is flammable over a wide range of vapor/air concentrations. Hydrogen is not toxic but is a simple asphyxiate by the displacement of oxygen in the air. Under prolonged exposure to fire or intense heat the containers may rupture violently and rocket. Hydrogen is used to make other chemicals and in oxyhydrogen welding and cutting.[1]
4 values
From CAMEO Chemicals, the most authoritative source here.
Value As written Source
–shown Hydrogen is a colorless, odorless gas. It is easily ignited. Once ignited it burns with a pale blue, almost invisible flame. The vapors are lighter than air. It is flammable over a wide range of vapor/air concentrations. Hydrogen is not toxic but is a simple asphyxiate by the displacement of oxygen in the air. Under prolonged exposure to fire or intense heat the containers may rupture violently and rocket. Hydrogen is used to make other chemicals and in oxyhydrogen welding and cutting. [1] CAMEO Chemicals
– Hydrogen, refrigerated liquid (cryogenic liquid) appears as a colorless very cold liquid shipped in special heavily insulated containers. Boils at -442 °F. Contact causes severe frostbite. Hydrogen gas at normal temperatures is lighter than air but until vapors boiling off from the liquid warm up they are heavier than air. Very easily ignited. Burns with a pale blue, almost invisible flame. A leak could be either a vapor or a liquid leak. The container is designed to vent the vapor as it is boils off. Under prolonged exposure to intense heat the containers may rupture violently and rocket. [1] CAMEO Chemicals
– Gas Vapor; Dry Powder; Wet Solid; Other Solid; CBI; Liquid; Gas Vapor; Liquid [2] EPA Chemical Data Reporting (CDR)
– ODOURLESS COLOURLESS COMPRESSED GAS. [3] ILO-WHO International Chemical Safety Cards (ICSCs)
Odor: Odorless[4]
Melting point: -259.18 °C[5]
4 values
3 of 3 sources agree on it (most common value).
Value As written Source
−259 °C -434 °F (USCG, 1999) [1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
−259 °C -434 °F (USCG, 1999) [1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
−259 °C -259 °C [3] ILO-WHO International Chemical Safety Cards (ICSCs)
−259.2 °Cshown -259.18 °C [5] PAC Chemical Database, U.S. Department of Energy
Boiling point: -252.8 °C @760 [mmHg][5]
4 values
3 of 3 sources agree on it (most common value).
Value As written Source
−253 °C -423 °F at 760 mmHg (USCG, 1999) [1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
−253 °C -423 °F at 760 mmHg (USCG, 1999) [1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
−253 °C -253 °C [3] ILO-WHO International Chemical Safety Cards (ICSCs)
−252.8 °Cshown -252.8 °C @760 [mm Hg] [5] PAC Chemical Database, U.S. Department of Energy
Density: 0.070 @ -253°C[5]
3 values
2 of 2 sources agree on it (most common value).
Value As written Source
– 0.071 at -423.4 °F (USCG, 1999) - Less dense than water [1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
– 0.071 at -423.4 °F (USCG, 1999) - Less dense than water [1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
–shown 0.070 @ -253°C [5] PAC Chemical Database, U.S. Department of Energy
Solubility in water: Solubility in water, mg/l at 21 °C: 1.62 (very poor)[3]
3 values
From ILO-WHO International Chemical Safety Cards (ICSCs), the most authoritative source here.
Value As written Source
– In water, 1.62 mg/L at 21 °C [4] Hazardous Substances Data Bank (HSDB)cites Venable CS, Fuwa T; Ind Eng Chem 14: 139-42 (1922)
– Very low solubility in most liquids [4] Hazardous Substances Data Bank (HSDB)cites Lewis, R.J. Sr. (ed) Sax's Dangerous Properties of Industrial Materials. 12th Edition. Wiley-Interscience, Wiley & Sons, Inc. Hoboken, NJ. 2012., p. V4: 2431
–shown Solubility in water, mg/l at 21 °C: 1.62 (very poor) [3] ILO-WHO International Chemical Safety Cards (ICSCs)
Vapor pressure: 1240000 [mmHg] @25 °C[5]
3 values
3 of 3 sources agree on it (most common value).
Value As written Source
1240000 mmHg 1.24X10+6 mm Hg at 25 °C [4] Hazardous Substances Data Bank (HSDB)cites Ohe S; Computer Aided Data Book of Vapor Pressure. Data Book Publ. Co, Tokyo, Japan (1976)
1200000 mmHg Vapor pressure, kPa at 25 °C: 165320 [3] ILO-WHO International Chemical Safety Cards (ICSCs)
1240000 mmHgshown 1240000 [mm Hg] @25 °C [5] PAC Chemical Database, U.S. Department of Energy
Autoignition temperature: 574 °C (1065 °F, USCG 1999)[1]
4 values
Sources disagree; from CAMEO Chemicals, the most authoritative.
Value As written Source
574 °Cshown 1065 °F (USCG, 1999) [1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
574 °C 1065 °F (USCG, 1999) [1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
500 °C 932 °F (500 °C) [4] Hazardous Substances Data Bank (HSDB)cites National Fire Protection Association; Fire Protection Guide to Hazardous Materials. 14TH Edition, Quincy, MA 2010, p. 325-72
560 °C 560 °C [3] ILO-WHO International Chemical Safety Cards (ICSCs)

Value	As written	Source
–shown	Hydrogen is a colorless, odorless gas. It is easily ignited. Once ignited it burns with a pale blue, almost invisible flame. The vapors are lighter than air. It is flammable over a wide range of vapor/air concentrations. Hydrogen is not toxic but is a simple asphyxiate by the displacement of oxygen in the air. Under prolonged exposure to fire or intense heat the containers may rupture violently and rocket. Hydrogen is used to make other chemicals and in oxyhydrogen welding and cutting.	[1] CAMEO Chemicals
–	Hydrogen, refrigerated liquid (cryogenic liquid) appears as a colorless very cold liquid shipped in special heavily insulated containers. Boils at -442 °F. Contact causes severe frostbite. Hydrogen gas at normal temperatures is lighter than air but until vapors boiling off from the liquid warm up they are heavier than air. Very easily ignited. Burns with a pale blue, almost invisible flame. A leak could be either a vapor or a liquid leak. The container is designed to vent the vapor as it is boils off. Under prolonged exposure to intense heat the containers may rupture violently and rocket.	[1] CAMEO Chemicals
–	Gas Vapor; Dry Powder; Wet Solid; Other Solid; CBI; Liquid; Gas Vapor; Liquid	[2] EPA Chemical Data Reporting (CDR)
–	ODOURLESS COLOURLESS COMPRESSED GAS.	[3] ILO-WHO International Chemical Safety Cards (ICSCs)

Value	As written	Source
−259 °C	-434 °F (USCG, 1999)	[1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
−259 °C	-434 °F (USCG, 1999)	[1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
−259 °C	-259 °C	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
−259.2 °Cshown	-259.18 °C	[5] PAC Chemical Database, U.S. Department of Energy

Value	As written	Source
−253 °C	-423 °F at 760 mmHg (USCG, 1999)	[1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
−253 °C	-423 °F at 760 mmHg (USCG, 1999)	[1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
−253 °C	-253 °C	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
−252.8 °Cshown	-252.8 °C @760 [mm Hg]	[5] PAC Chemical Database, U.S. Department of Energy

Value	As written	Source
–	0.071 at -423.4 °F (USCG, 1999) - Less dense than water	[1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
–	0.071 at -423.4 °F (USCG, 1999) - Less dense than water	[1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
–shown	0.070 @ -253°C	[5] PAC Chemical Database, U.S. Department of Energy

Value	As written	Source
–	In water, 1.62 mg/L at 21 °C	[4] Hazardous Substances Data Bank (HSDB)cites Venable CS, Fuwa T; Ind Eng Chem 14: 139-42 (1922)
–	Very low solubility in most liquids	[4] Hazardous Substances Data Bank (HSDB)cites Lewis, R.J. Sr. (ed) Sax's Dangerous Properties of Industrial Materials. 12th Edition. Wiley-Interscience, Wiley & Sons, Inc. Hoboken, NJ. 2012., p. V4: 2431
–shown	Solubility in water, mg/l at 21 °C: 1.62 (very poor)	[3] ILO-WHO International Chemical Safety Cards (ICSCs)

Value	As written	Source
1240000 mmHg	1.24X10+6 mm Hg at 25 °C	[4] Hazardous Substances Data Bank (HSDB)cites Ohe S; Computer Aided Data Book of Vapor Pressure. Data Book Publ. Co, Tokyo, Japan (1976)
1200000 mmHg	Vapor pressure, kPa at 25 °C: 165320	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
1240000 mmHgshown	1240000 [mm Hg] @25 °C	[5] PAC Chemical Database, U.S. Department of Energy

Value	As written	Source
574 °Cshown	1065 °F (USCG, 1999)	[1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
574 °C	1065 °F (USCG, 1999)	[1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
500 °C	932 °F (500 °C)	[4] Hazardous Substances Data Bank (HSDB)cites National Fire Protection Association; Fire Protection Guide to Hazardous Materials. 14TH Edition, Quincy, MA 2010, p. 325-72
560 °C	560 °C	[3] ILO-WHO International Chemical Safety Cards (ICSCs)

Each value as its source reports it, with the source's number after it (listed under References). Where several sources report a property, the row shows the value most of them agree on, the rule the app uses; open the values to see every one.

Calculated

Heavy atoms: 0
Rings: 0
Aromatic rings: 0
Fraction sp³ carbons (Fsp3): 0
H-bond donors: 0
H-bond acceptors: 0
Rotatable bonds: 0
TPSA (Å²): 0
Formal charge: 0
XLogP3: 0 PubChem
Complexity: 0 PubChem
Stereocenters: None
Double-bond geometry: None specified
Point group: D∞h of one 3D conformer with its hydrogens, by Athanor’s engine (as in the app)

Elemental analysis

H100.00%

Isotope pattern

Each peak is a nominal mass with its abundance-weighted exact mass, as a percentage of the tallest, from IUPAC natural isotope abundances.

Computed from the structure with RDKit 2026.09 when this page was built, beside PubChem's own computed values from its record; where the two differ, both are shown.

Predicted

log P: 0.25 Crippen (Wildman and Crippen 1999)
log S (water solubility): -0.01 ESOL (Delaney 2004), log mol/L
Synthetic accessibility: 7.03 SA score, 1 easy to 10 hard (Ertl and Schuffenhauer 2009)

Drug-likeness: Lipinski’s rule of five

Molecular weight ≤ 500: 2.02
log P ≤ 5 (Crippen): 0.25
H-bond donors ≤ 5: 0
H-bond acceptors ≤ 10: 0

Passes all four rules.

Predictions, not measurements; each names its method. A measured log P, where a source reports one, is under Physical properties.

Safety

Danger

Harmonized EU classification (CLP Annex VI). Source [6].

Flammable
Compressed gas

NFPA 704[4]

H220Extremely flammable gas

Precautionary statements: P203, P210, P222, P280, P377, P381, P403

View all classifications (4)

[6] Regulation (EC) No 1272/2008 of the European Parliament and of the Council · DangerH220
[7] European Chemicals Agency (ECHA)This chemical does not meet GHS hazard criteria for 0.1% (2 of 1422) of reports.
[7] European Chemicals Agency (ECHA) · 1,422 reports · DangerH220, H280, H281
[4] Hazardous Substances Data Bank (HSDB) · DangerH220, H280

First aid

Excerpt from ERG Guide 115 [Gases - Flammable (Including Refrigerated Liquids)]: Refer to the "General First Aid" section. Specific First Aid: Clothing frozen to the skin should be thawed before being removed. In case of contact with liquefied gas, only medical personnel should attempt thawing frosted parts. In case of burns, immediately cool affected skin for as long as possible with cold water. Do not remove clothing if adhering to skin. (ERG, 2024)[1]
The only effect of exposure to liquid hydrogen is that caused by its unusually low temperature and its action as a simple asphyxiant. Inhalation: If victim is unconscious (due to oxygen deficiency), move him to fresh air and apply resuscitation methods; call physician. Eyes: Treat for frostbite. Skin: Treat for frostbite; soak in lukewarm water; get medical attention if burn is severe. (USCG, 1999)[1]
General First Aid: · Call 911 or emergency medical service. · Ensure that medical personnel are aware of the material(s) involved, take precautions to protect themselves and avoid contamination. · Move victim to fresh air if it can be done safely. · Administer oxygen if breathing is difficult. · If victim is not breathing: -- DO NOT perform mouth-to-mouth resuscitation; the victim may have ingested or inhaled the substance. -- If equipped and pulse detected, wash face and mouth, then give artificial respiration using a proper respiratory medical device (bag-valve mask, pocket mask equipped…[8]
General First Aid: · Call 911 or emergency medical service. · Ensure that medical personnel are aware of the material(s) involved, take precautions to protect themselves and avoid contamination. · Move victim to fresh air if it can be done safely. · Administer oxygen if breathing is difficult. · If victim is not breathing: -- DO NOT perform mouth-to-mouth resuscitation; the victim may have ingested or inhaled the substance. -- If equipped and pulse detected, wash face and mouth, then give artificial respiration using a proper respiratory medical device (bag-valve mask, pocket mask equipped…[8]

Storage

Fireproof. Cool. Ventilation along the floor and ceiling. Separated from oxidizing materials.[3]
Store in a cool, dry, well-ventilated location. Outside or detached storage is preferred. Isolate from oxygen, halogens, other oxidizing materials. (hydrogen, refrigerated liquid)[4]
A safe storage method for hydrogen for possible use as automotive fuel involves the use of metal hydrides from which the hydrogen is released at specified temperatures. Iron titanium hydride has been found the most satisfactory.[4]
Keep container tightly closed in a dry and well-ventilated place. Contents under pressure. Storage class (TRGS 510): Gases[4]

Incompatibilities

Release of hydrogen @ 47.5 bar into a vented 17.5-l chromium-plated sphere caused explosive ignition. (hydrogen)[4]
Hydrogen ignites in bromine fluoride at ambient temp.[4]
Mixtures of iodine heptafluoride with hydrogen explode on heating or sparking.[4]
... Calcium, barium, and strontium react readily, sometimes igniting, in hydrogen above 300 °C. ...[4]

Safety data sheets on the supplier’s page: Shenghe Chemical, Alfa Chemistry, Cooke Chemical Co., Ltd.

Always read the supplier’s safety data sheet before working with it.

Spectra

GC-MSNIST Mass Spectrometry Data Center · SpectraBase

Experimental spectra held by these sources; each link opens the source's own record.

Literature

Reading PubChem, OpenAlex and GSRS…

Bioactivity

Reading ChEMBL…

References

[1]CAMEO Chemicals · Public domain (NOAA) · via PubChem · retrieved 2026-10-14
[2]EPA Chemical Data Reporting (CDR) · Public domain (US EPA) · via PubChem · retrieved 2026-10-14
[3]ILO-WHO International Chemical Safety Cards (ICSCs) · CC BY 4.0 · via PubChem · retrieved 2026-10-14
[4]Hazardous Substances Data Bank (HSDB) · Public domain (US NLM) · via PubChem · retrieved 2026-10-14
[5]PAC Chemical Database, U.S. Department of Energy · Public domain (US DOE) · via PubChem · retrieved 2026-10-14
[6]Regulation (EC) No 1272/2008 of the European Parliament and of the Council · EU reuse policy, CC BY 4.0 · via PubChem · retrieved 2026-10-14
[7]European Chemicals Agency (ECHA) · ECHA legal notice: reuse with acknowledgement · via PubChem · retrieved 2026-10-14
[8]Emergency Response Guidebook (ERG) · Public domain (US DOT) · via PubChem · retrieved 2026-10-14
[9]NIST Mass Spectrometry Data Center · Linked only · via PubChem · retrieved 2026-10-14
[10]SpectraBase · Linked only · via PubChem · retrieved 2026-10-14
·Calculated values: computed by Athanor with RDKit 2026.09 from the structure.
·Literature on PubChem

Data last updated 2026-10-14.