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Chlorine

Athanor · official

Cl2 · 70.9 g/mol

IUPAC name: molecular chlorine

Also called dichlorine, molecular chlorine

Open in Athanor
The structure of Chlorine
Drawn from its SMILES with RDKit000OX
OxidizerCompressed gasAcute toxicityEnvironmental hazardDangerMay cause or intensify fire; oxidizer · Causes skin irritation · Causes serious eye irritation · Toxic if inhaled · May cause respiratory irritation · Very toxic to aquatic life

Names and identifiers

IUPAC name
molecular chlorine
Synonyms
dichlorine, molecular chlorine, Molecular chlorine
+ 35 more

Bertholite, Chlorine gas, Chlorinum, Chloor, Chlore, Chlor, Cloro, Chlorine mol., Chlorine 35, UN 1017, DTXSID1020273, 4R7X1O2820, CHEBI:29310, Gas, Chlorine, Cl2 Gas, Gas, Cl2, dichlorane, Total Chlorine, Dietary Chlorine, HBA Disinfectant, Disinfectant(NaClO), RefChem:6407, DTXCID50273, CHEBI:33432, D-150, 231-959-5, CHEBI:23116, Chlorine-35, Cl, CL2, SCHEMBL124, Chlore [French], Cloro [Italian], Chloor [Dutch], Chlor [German]

Molecular formula
Cl2
Empirical formula
Cl
Molecular weight
70.9 g/mol
Exact mass
69.93771
CAS number
7782-50-5
PubChem CID
24526
Canonical SMILES
ClCl
Isomeric SMILES
ClCl
InChI
InChI=1S/Cl2/c1-2
InChIKey
KZBUYRJDOAKODT-UHFFFAOYSA-N
Molfile

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

Physical properties

TemperaturePressureDensity
Appearance
Greenish-yellow gas ... [Note: Shipped as a liquefied compressed gas][6]
7 values

From Hazardous Substances Data Bank (HSDB), the most authoritative source here.

ValueAs writtenSource
–Chlorine appears as a greenish yellow gas with a pungent suffocating odor. Toxic by inhalation. Slightly soluble in water. Liquefies at -35 °C and room pressure. Readily liquefied by pressure applied at room temperature. Contact with unconfined liquid can cause frostbite by evaporative cooling. Does not burn but, like oxygen, supports combustion. Long-term inhalation of low concentrations or short-term inhalation of high concentrations has ill effects. Vapors are much heavier than air and tend to settle in low areas. Contact CHEMTREC to activate chlorine response team 800-424-9300. Used to pur[1] CAMEO Chemicals
–CBI; Gas Vapor; Gas Vapor; Liquid; Liquid[2] EPA Chemical Data Reporting (CDR)
–GREENISH-YELLOW COMPRESSED LIQUEFIED GAS WITH PUNGENT ODOUR.[3] ILO-WHO International Chemical Safety Cards (ICSCs)
–Greenish-yellow gas with a pungent, irritating odor.[4] Occupational Safety and Health Administration (OSHA)
–Greenish-yellow gas with a pungent, irritating odor. [Note: Shipped as a liquefied compressed gas.][5] The National Institute for Occupational Safety and Health (NIOSH)
–Greenish-yellow gas at room temperature; clear, amber-colored liquid under increased pressure or at temperatures below -30°F (-34°C).[5] The National Institute for Occupational Safety and Health (NIOSH)
–shownGreenish-yellow gas ... [Note: Shipped as a liquefied compressed gas][6] Hazardous Substances Data Bank (HSDB)cites NIOSH. NIOSH Pocket Guide to Chemical Hazards. Department of Health & Human Services, Centers for Disease Control & Prevention. National Institute for Occupational Safety & Health. DHHS (NIOSH) Publication No. 2010-168 (2010). Available from: https://www.cdc.gov/niosh/npg
Odor
Pungent, irritating[6]
3 values

From Hazardous Substances Data Bank (HSDB), the most authoritative source here.

ValueAs writtenSource
–shownPungent, irritating[6] Hazardous Substances Data Bank (HSDB)cites NIOSH. NIOSH Pocket Guide to Chemical Hazards. Department of Health & Human Services, Centers for Disease Control & Prevention. National Institute for Occupational Safety & Health. DHHS (NIOSH) Publication No. 2010-168 (2010). Available from: https://www.cdc.gov/niosh/npg
–Odor like concentrated bleach[6] Hazardous Substances Data Bank (HSDB)cites Compton JAF; Military Chemical and Biological Agents. Chemical and Toxicological Properties. Caldwell, NJ: Telford Press, pp. 113-118 (1987)
–Irritating, bleach-like choking odor[6] Hazardous Substances Data Bank (HSDB)cites NOAA; CAMEO Chemicals. Database of Hazardous Materials. Chlorine (7782-50-5). Natl Ocean Atmos Admin, Off Resp Rest; NOAA Ocean Serv. Available from, as of July 8, 2016: https://cameochemicals.noaa.gov/
Melting point
-101.5 °C[7]
5 values

5 of 5 sources agree on it (most common value).

ValueAs writtenSource
−101 °C-150 °F (EPA, 1998)[1] CAMEO Chemicalscites U.S. Environmental Protection Agency. 1998. Extremely Hazardous Substances (EHS) Chemical Profiles and Emergency First Aid Guides. Washington, D.C.: U.S. Government Printing Office.
−101 °C-101 °C[3] ILO-WHO International Chemical Safety Cards (ICSCs)
−101 °C-150 °F[4] Occupational Safety and Health Administration (OSHA)
−101.5 °Cshown-101.5 °C[7] PAC Chemical Database, U.S. Department of Energy
−101 °C-150 °F[5] The National Institute for Occupational Safety and Health (NIOSH)
Boiling point
-34.04 °C @760 [mmHg][7]
5 values

5 of 5 sources agree on it (most common value).

ValueAs writtenSource
−34.6 °C-30.3 °F at 760 mmHg (EPA, 1998)[1] CAMEO Chemicalscites U.S. Environmental Protection Agency. 1998. Extremely Hazardous Substances (EHS) Chemical Profiles and Emergency First Aid Guides. Washington, D.C.: U.S. Government Printing Office.
−34 °C-34 °C[3] ILO-WHO International Chemical Safety Cards (ICSCs)
−34 °C-29 °F[4] Occupational Safety and Health Administration (OSHA)
−34.0 °Cshown-34.04 °C @760 [mm Hg][7] PAC Chemical Database, U.S. Department of Energy
−34 °C-29 °F[5] The National Institute for Occupational Safety and Health (NIOSH)
Density
density: 3.213 kg/cu m at 0 °C and 101.3 kPa[6]
8 values

Sources disagree; from Hazardous Substances Data Bank (HSDB), the most authoritative.

ValueAs writtenSource
–1.424 at 59 °F (pressurized liquid) (USCG, 1999) - Denser 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.
0.003213 g/mLshowndensity: 3.213 kg/cu m at 0 °C and 101.3 kPa[6] Hazardous Substances Data Bank (HSDB)cites Bommaraju TV et al; Chlorine. Kirk-Othmer Encyclopedia of Chemical Technology. (1999-2016). New York, NY: John Wiley & Sons. Online Posting Date: 2 Nov 2002.
–23.80 eV[6] Hazardous Substances Data Bank (HSDB)cites Bommaraju TV et al; Chlorine. Kirk-Othmer Encyclopedia of Chemical Technology. (1999-2016). New York, NY: John Wiley & Sons. Online Posting Date: 2 Nov 2002.
–density: 1.56 at -35 °C, freezing point: -101 °C[6] Hazardous Substances Data Bank (HSDB)cites Larranaga, M.D., Lewis, R.J. Sr., Lewis, R.A.; Hawley's Condensed Chemical Dictionary 16th Edition. John Wiley & Sons, Inc. Hoboken, NJ 2016., p. 305
–1 L liquid = 456.8 L gas at 0 °C and 1 atm[6] Hazardous Substances Data Bank (HSDB)cites Larranaga, M.D., Lewis, R.J. Sr., Lewis, R.A.; Hawley's Condensed Chemical Dictionary 16th Edition. John Wiley & Sons, Inc. Hoboken, NJ 2016., p. 305
–1.424 at 59 °F[4] Occupational Safety and Health Administration (OSHA)
0.002898 g/mL2.898g/L[7] PAC Chemical Database, U.S. Department of Energy
–2.47(relative gas density)[5] The National Institute for Occupational Safety and Health (NIOSH)

18 more values were reported but failed the checks (unreadable or out of range), so they are not shown.

Solubility in water
Solubility in water, g/100ml at 20 °C: 0.7[3]
4 values

From ILO-WHO International Chemical Safety Cards (ICSCs), the most authoritative source here.

ValueAs writtenSource
–0.7 % (NIOSH, 2024)[1] CAMEO Chemicals
–In water, 6,300 mg/L at 25 °C[6] Hazardous Substances Data Bank (HSDB)cites PMID:6376602 Amoore JE, Hautala E; J Appl Toxicol 3: 272-90 (1983)
–shownSolubility in water, g/100ml at 20 °C: 0.7[3] ILO-WHO International Chemical Safety Cards (ICSCs)
–0.7%[5] The National Institute for Occupational Safety and Health (NIOSH)
Vapor pressure
7600 mmHg at 30 °C (86 °F, EPA 1998)[1]
3 values

Sources disagree; from CAMEO Chemicals, the most authoritative.

ValueAs writtenSource
7600 mmHgshown7600 mmHg at 86 °F (EPA, 1998)[1] CAMEO Chemicalscites U.S. Environmental Protection Agency. 1998. Extremely Hazardous Substances (EHS) Chemical Profiles and Emergency First Aid Guides. Washington, D.C.: U.S. Government Printing Office.
5830 mmHg5.83X10+3 mm Hg at 25 °C[6] Hazardous Substances Data Bank (HSDB)cites Daubert, T.E., R.P. Danner. Physical and Thermodynamic Properties of Pure Chemicals Data Compilation. Washington, D.C.: Taylor and Francis, 1989.
5000 mmHgVapor pressure, kPa at 20 °C: 673[3] ILO-WHO International Chemical Safety Cards (ICSCs)

2 more values were reported but failed the checks (unreadable or out of range), so they are not shown.

Autoignition temperature
Reported, but no value passed the checks.
The value and why
  • Not flammable (USCG, 1999) (could not be read; source [1])
Viscosity
Reported, but no value passed the checks.
The 2 values and why
  • 0.134 mPa.sec at 20 °C (gas) (could not be read; source [6])
  • 0.346 mPa.sec at 20 °C (liquid) (could not be read; source [6])

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
2
Rings
0
Aromatic rings
0
Fraction sp³ carbons (Fsp3)
0
H-bond donors
0
H-bond acceptors
0
Rotatable bonds
0
TPSA (Ų)
0
Formal charge
0
XLogP3
1.6 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

  • Cl100.00%

Isotope pattern

100%69.93864%71.93510%73.932

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
1.38 Crippen (Wildman and Crippen 1999)
log S (water solubility)
-1.15 ESOL (Delaney 2004), log mol/L
Synthetic accessibility
3.97 SA score, 1 easy to 10 hard (Ertl and Schuffenhauer 2009)

Drug-likeness: Lipinski’s rule of five

  • Molecular weight ≤ 500: 70.91
  • log P ≤ 5 (Crippen): 1.38
  • 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 [8].

  • Oxidizer
  • Compressed gas
  • Acute toxicity
  • Environmental hazard
000OX
NFPA 704[4]
  • H270May cause or intensify fire; oxidizer
  • H315Causes skin irritation
  • H319Causes serious eye irritation
  • H331Toxic if inhaled
  • H335May cause respiratory irritation
  • H400Very toxic to aquatic life

Precautionary statements: P220, P244, P261, P264, P264+P265, P271, P273, P280, P302+P352, P304+P340, P305+P351+P338, P316, P319, P321, P332+P317, P337+P317, P362+P364, P370+P376, P391, P403, P403+P233, P405, P501

View all classifications (3)
  • [8] Regulation (EC) No 1272/2008 of the European Parliament and of the Council · DangerH270, H315, H319, H331, H335, H400
  • [9] European Chemicals Agency (ECHA) · 1,089 reports · DangerH270, H280, H330, H331, H335, H400, H410
  • [6] Hazardous Substances Data Bank (HSDB) · DangerH270, H280, H315, H319, H331, H335, H400

Exposure limits

  • PEL-TWA (8-Hour Time Weighted Average): 1 ppm (3 mg/m³) [Construction and Maritime Industries only][4]
  • PEL-C (Ceiling): 1 ppm (3 mg/m³) [General Industry only][4]
  • PEL: C 1 ppm (3 mg/m3) See Appendix G[5]
  • REL-C (Ceiling): 0.5 ppm (1.45 mg/m³) [15 minutes][4]
  • REL: C 0.5 ppm (1.45 mg/m3) [15-minute][5]
  • TLV: 0.1 ppm as TWA; 0.4 ppm as STEL; A4 (not classifiable as a human carcinogen).[3]

First aid

  • Warning: Effects may be delayed. Caution is advised. Chlorine is corrosive and may be converted to hydrochloric acid in the lungs. Signs and Symptoms of Acute Chlorine Exposure: Signs and symptoms of acute exposure to chlorine may include tachycardia (rapid heart rate), hypertension (high blood pressure) followed by hypotension (low blood pressure), and cardiovascular collapse. Pulmonary edema and pneumonia are often seen. The eyes, nose, throat, and chest may sting or burn following exposure to chlorine.[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…[10]
  • (General first aid procedures) Eye: Frostbite - If eye tissue is frozen, seek medical attention immediately; if tissue is not frozen, immediately and thoroughly flush the eyes with large amounts of water for at least 15 minutes, occasionally lifting the lower and upper eyelids. If irritation, pain, swelling, lacrimation, or photophobia persist, get medical attention as soon as possible. Skin: Frostbite - Compressed gases may create low temperatures when they expand rapidly. Leaks and uses that allow rapid expansion may cause a frostbite hazard.[5]
  • Fresh air, rest. Half-upright position. Refer immediately for medical attention. Artificial respiration may be needed.[3]

Storage

  • Fireproof if in building. Provision to contain effluent from fire extinguishing. Separated from food and feedstuffs. See Chemical Dangers. Cool. Dry. Keep in a well-ventilated room. Store in an area without drain or sewer access.[3]
  • Keep container tightly closed in a dry and well-ventilated place. Contents under pressure. Storage class (TRGS 510): Gases.[6]
  • Store in a cool, dry, well-ventilated location. Separate from combustible, organic, or easily oxidizable materials. Isolate from acetylene, ammonia, hydrogen, hydrocarbons, ether, turpentine, and finely divided metals. Outside or detached storage is preferred.[6]
  • Permanent storage of chlorine is generally not recommended. However, at chlorine producing plants and barge shipping terminals, chlorine storage is an obvious necessity. Moderate amt may be handled in high strength tanks as a liquefied gas under pressure. The max amt that is considered safe under these conditions is about 450 tons. For larger quantities, low temp storage at atmosphere pressure is preferred in the interest of safety as well as economy. Chlorine gas evaporating from the low temp storage tank is reliquefied by a small refrigeration unit and recycled to storage.[6]

Incompatibilities

  • Incompatible materials: Alcohols.[6]
  • Antimony burns spontaneously in gaseous chlorine; with liquid chlorine, antimony ignites at 33 °C.[6]
  • Arsenic burns spontaneously in gaseous chlorine; with liquid chlorine, arsenic ignites at 33 °C.[6]
  • Arsenic disulfide ignites in a rapid stream of chlorine.[6]

Safety data sheets on the supplier’s page: Smolecule, AppChem, LGC Standards.

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

Spectra

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. [1]CAMEO Chemicals · Public domain (NOAA) · via PubChem · retrieved 2026-10-14
  2. [2]EPA Chemical Data Reporting (CDR) · Public domain (US EPA) · via PubChem · retrieved 2026-10-14
  3. [3]ILO-WHO International Chemical Safety Cards (ICSCs) · CC BY 4.0 · via PubChem · retrieved 2026-10-14
  4. [4]Occupational Safety and Health Administration (OSHA) · Public domain (US DOL) · via PubChem · retrieved 2026-10-14
  5. [5]The National Institute for Occupational Safety and Health (NIOSH) · Public domain (US CDC) · via PubChem · retrieved 2026-10-14
  6. [6]Hazardous Substances Data Bank (HSDB) · Public domain (US NLM) · via PubChem · retrieved 2026-10-14
  7. [7]PAC Chemical Database, U.S. Department of Energy · Public domain (US DOE) · via PubChem · retrieved 2026-10-14
  8. [8]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
  9. [9]European Chemicals Agency (ECHA) · ECHA legal notice: reuse with acknowledgement · via PubChem · retrieved 2026-10-14
  10. [10]Emergency Response Guidebook (ERG) · Public domain (US DOT) · via PubChem · retrieved 2026-10-14
  11. [11]NIST Mass Spectrometry Data Center · Linked only · via PubChem · retrieved 2026-10-14
  12. [12]SpectraBase · Linked only · via PubChem · retrieved 2026-10-14
  13. ·Calculated values: computed by Athanor with RDKit 2026.09 from the structure.
  14. ·Literature on PubChem

Data last updated 2026-10-14.