{"title":"List of diatomic molecules and monatomic elements","description":"A reference list of true diatomic molecules (the seven elemental diatomics, heteronuclear and interhalogen molecules, and reactive gas-phase species) and the monatomic noble gases, with formulas and PubChem identifiers.","slug":"diatomic-and-monatomic-elements","url":"https://proteiniq.io/datasets/diatomic-and-monatomic-elements","version":"2026.10.05","updatedAt":"2026-10-05","license":{"id":"CC-BY-4.0","name":"Creative Commons Attribution 4.0 International","url":"https://creativecommons.org/licenses/by/4.0/"},"attribution":"List of diatomic molecules and monatomic elements by ProteinIQ (https://proteiniq.io/datasets/diatomic-and-monatomic-elements), compiled from PubChem, NIST Chemistry WebBook, OpenStax Chemistry. Licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/).","citation":"ProteinIQ (2026). List of diatomic molecules and monatomic elements, version 2026.10.05. https://proteiniq.io/datasets/diatomic-and-monatomic-elements","sources":[{"name":"PubChem","url":"https://pubchem.ncbi.nlm.nih.gov/","role":"Canonical compound identifiers, names, formulas, structures, SMILES, and downloadable compound records.","licenseNote":"NCBI places no restrictions on PubChem data, though original submitters may retain rights in submitted records."},{"name":"NIST Chemistry WebBook","url":"https://webbook.nist.gov/chemistry/","role":"Reference physical chemistry data and diatomic constants for selected species.","licenseNote":"NIST SRD 69 should be cited and linked rather than mirrored wholesale."},{"name":"OpenStax Chemistry","url":"https://openstax.org/details/books/chemistry-2e","role":"Chemistry definitions used for educational polarity, bonding, organic chemistry, and molecule-class explanations."}],"columns":[{"key":"name","label":"Name"},{"key":"formula","label":"Formula"},{"key":"molecularWeight","label":"MW (g/mol)"},{"key":"classification","label":"Classification"},{"key":"category","label":"Type"},{"key":"smiles","label":"SMILES"},{"key":"pubchemCid","label":"PubChem CID"},{"key":"sourceIds","label":"Source IDs"},{"key":"notes","label":"Notes"}],"rowCount":43,"rows":[{"id":"hydrogen","name":"Hydrogen","formula":"H2","molecularWeight":2.02,"classification":"Diatomic molecule","category":"Elemental diatomic (homonuclear)","smiles":"[HH]","pubchemCid":"783","sourceIds":["PubChem CID 783"],"notes":"One of the seven elements that exist as diatomic molecules under ordinary conditions."},{"id":"nitrogen","name":"Nitrogen","formula":"N2","molecularWeight":28.01,"classification":"Diatomic molecule","category":"Elemental diatomic (homonuclear)","smiles":"N#N","pubchemCid":"947","sourceIds":["PubChem CID 947"],"notes":"Triple-bonded; about 78% of dry air by volume."},{"id":"oxygen","name":"Oxygen","formula":"O2","molecularWeight":32,"classification":"Diatomic molecule","category":"Elemental diatomic (homonuclear)","smiles":"O=O","pubchemCid":"977","sourceIds":["PubChem CID 977"],"notes":"Paramagnetic because of two unpaired electrons."},{"id":"fluorine","name":"Fluorine","formula":"F2","molecularWeight":38,"classification":"Diatomic molecule","category":"Elemental diatomic (homonuclear)","smiles":"FF","pubchemCid":"24524","sourceIds":["PubChem CID 24524"],"notes":"Pale yellow gas; the most reactive element."},{"id":"chlorine","name":"Chlorine","formula":"Cl2","molecularWeight":70.9,"classification":"Diatomic molecule","category":"Elemental diatomic (homonuclear)","smiles":"ClCl","pubchemCid":"24526","sourceIds":["PubChem CID 24526"],"notes":"Yellow-green gas at room temperature."},{"id":"bromine","name":"Bromine","formula":"Br2","molecularWeight":159.81,"classification":"Diatomic molecule","category":"Elemental diatomic (homonuclear)","smiles":"BrBr","pubchemCid":"24408","sourceIds":["PubChem CID 24408"],"notes":"Red-brown liquid at room temperature."},{"id":"iodine","name":"Iodine","formula":"I2","molecularWeight":253.8,"classification":"Diatomic molecule","category":"Elemental diatomic (homonuclear)","smiles":"II","pubchemCid":"807","sourceIds":["PubChem CID 807"],"notes":"Dark violet solid that sublimes to a violet vapor."},{"id":"helium","name":"Helium","formula":"He","molecularWeight":4,"classification":"Monatomic element","category":"Noble gas","smiles":"[He]","pubchemCid":"23987","sourceIds":["PubChem CID 23987"]},{"id":"neon","name":"Neon","formula":"Ne","molecularWeight":20.18,"classification":"Monatomic element","category":"Noble gas","smiles":"[Ne]","pubchemCid":"23935","sourceIds":["PubChem CID 23935"]},{"id":"argon","name":"Argon","formula":"Ar","molecularWeight":39.95,"classification":"Monatomic element","category":"Noble gas","smiles":"[Ar]","pubchemCid":"23968","sourceIds":["PubChem CID 23968"]},{"id":"krypton","name":"Krypton","formula":"Kr","molecularWeight":83.8,"classification":"Monatomic element","category":"Noble gas","smiles":"[Kr]","pubchemCid":"5416","sourceIds":["PubChem CID 5416"]},{"id":"xenon","name":"Xenon","formula":"Xe","molecularWeight":131.29,"classification":"Monatomic element","category":"Noble gas","smiles":"[Xe]","pubchemCid":"23991","sourceIds":["PubChem CID 23991"]},{"id":"radon","name":"Radon","formula":"Rn","molecularWeight":222,"classification":"Monatomic element","category":"Noble gas","smiles":"[Rn]","pubchemCid":"24857","sourceIds":["PubChem CID 24857"],"notes":"Radioactive."},{"id":"carbon-monoxide","name":"Carbon monoxide","formula":"CO","molecularWeight":28.01,"classification":"Diatomic molecule","category":"Heteronuclear diatomic molecule","smiles":"[C-]#[O+]","pubchemCid":"281","sourceIds":["PubChem CID 281"]},{"id":"nitric-oxide","name":"Nitric oxide","formula":"NO","molecularWeight":30.01,"classification":"Diatomic molecule","category":"Heteronuclear diatomic molecule","smiles":"[N]=O","pubchemCid":"145068","sourceIds":["PubChem CID 145068"],"notes":"A stable free radical with one unpaired electron."},{"id":"hydrogen-fluoride","name":"Hydrogen fluoride","formula":"HF","molecularWeight":20.01,"classification":"Diatomic molecule","category":"Heteronuclear diatomic molecule","smiles":"F","pubchemCid":"14917","sourceIds":["PubChem CID 14917"]},{"id":"hydrogen-chloride","name":"Hydrogen chloride","formula":"HCl","molecularWeight":36.46,"classification":"Diatomic molecule","category":"Heteronuclear diatomic molecule","smiles":"Cl","pubchemCid":"313","sourceIds":["PubChem CID 313"],"notes":"Hydrochloric acid is its solution in water."},{"id":"hydrogen-bromide","name":"Hydrogen bromide","formula":"HBr","molecularWeight":80.91,"classification":"Diatomic molecule","category":"Heteronuclear diatomic molecule","smiles":"Br","pubchemCid":"260","sourceIds":["PubChem CID 260"]},{"id":"hydrogen-iodide","name":"Hydrogen iodide","formula":"HI","molecularWeight":127.91,"classification":"Diatomic molecule","category":"Heteronuclear diatomic molecule","smiles":"I","pubchemCid":"24841","sourceIds":["PubChem CID 24841"]},{"id":"chlorine-monofluoride","name":"Chlorine monofluoride","formula":"ClF","molecularWeight":54.45,"classification":"Diatomic molecule","category":"Interhalogen diatomic molecule","smiles":"FCl","pubchemCid":"123266","sourceIds":["PubChem CID 123266"]},{"id":"bromine-monochloride","name":"Bromine monochloride","formula":"BrCl","molecularWeight":115.35,"classification":"Diatomic molecule","category":"Interhalogen diatomic molecule","smiles":"ClBr","pubchemCid":"61697","sourceIds":["PubChem CID 61697"],"notes":"Exists in equilibrium with Br2 and Cl2."},{"id":"iodine-monochloride","name":"Iodine monochloride","formula":"ICl","molecularWeight":162.35,"classification":"Diatomic molecule","category":"Interhalogen diatomic molecule","smiles":"ClI","pubchemCid":"24640","sourceIds":["PubChem CID 24640"]},{"id":"iodine-monobromide","name":"Iodine monobromide","formula":"IBr","molecularWeight":206.8,"classification":"Diatomic molecule","category":"Interhalogen diatomic molecule","smiles":"BrI","pubchemCid":"82238","sourceIds":["PubChem CID 82238"]},{"id":"bromine-monofluoride","name":"Bromine monofluoride","formula":"BrF","molecularWeight":98.9,"classification":"Diatomic molecule","category":"Interhalogen diatomic molecule","smiles":"FBr","pubchemCid":"139632","sourceIds":["PubChem CID 139632"],"notes":"Unstable; disproportionates into bromine and higher bromine fluorides."},{"id":"iodine-monofluoride","name":"Iodine monofluoride","formula":"IF","molecularWeight":145.9,"classification":"Diatomic molecule","category":"Interhalogen diatomic molecule","smiles":"FI","pubchemCid":"139637","sourceIds":["PubChem CID 139637"],"notes":"Unstable; disproportionates into iodine and iodine pentafluoride."},{"id":"hydroxyl-radical","name":"Hydroxyl radical","formula":"OH","molecularWeight":17.01,"classification":"Diatomic molecule","category":"Reactive or high-temperature diatomic","smiles":"[OH]","pubchemCid":"157350","sourceIds":["PubChem CID 157350"],"notes":"Short-lived radical and the main daytime oxidant in the atmosphere."},{"id":"cyano-radical","name":"Cyano radical","formula":"CN","molecularWeight":26.02,"classification":"Diatomic molecule","category":"Reactive or high-temperature diatomic","smiles":"[C]#N","pubchemCid":"5359238","sourceIds":["PubChem CID 5359238"],"notes":"Short-lived radical seen in flames, comets, and interstellar space."},{"id":"chlorine-monoxide","name":"Chlorine monoxide","formula":"ClO","molecularWeight":51.45,"classification":"Diatomic molecule","category":"Reactive or high-temperature diatomic","smiles":"[O]Cl","pubchemCid":"166686","sourceIds":["PubChem CID 166686"],"notes":"Radical involved in catalytic destruction of stratospheric ozone."},{"id":"sulfur-monoxide","name":"Sulfur monoxide","formula":"SO","molecularWeight":48.06,"classification":"Diatomic molecule","category":"Reactive or high-temperature diatomic","smiles":"O=S","pubchemCid":"114845","sourceIds":["PubChem CID 114845"],"notes":"Short-lived; persists only at low pressure."},{"id":"silicon-monoxide","name":"Silicon monoxide","formula":"SiO","molecularWeight":44.08,"classification":"Diatomic molecule","category":"Reactive or high-temperature diatomic","smiles":"O=[Si]","pubchemCid":"66241","sourceIds":["PubChem CID 66241"],"notes":"Exists as a molecule in the gas phase at high temperature and in interstellar space."},{"id":"phosphorus-monoxide","name":"Phosphorus monoxide","formula":"PO","molecularWeight":46.97,"classification":"Diatomic molecule","category":"Reactive or high-temperature diatomic","smiles":"O=[P]","pubchemCid":"6857426","sourceIds":["PubChem CID 6857426"]},{"id":"carbon-monosulfide","name":"Carbon monosulfide","formula":"CS","molecularWeight":44.07,"classification":"Diatomic molecule","category":"Reactive or high-temperature diatomic","smiles":"[C-]#[S+]","pubchemCid":"108054","sourceIds":["PubChem CID 108054"],"notes":"Sulfur analog of carbon monoxide; observed in interstellar space."},{"id":"boron-monoxide","name":"Boron monoxide","formula":"BO","molecularWeight":26.81,"classification":"Diatomic molecule","category":"Reactive or high-temperature diatomic","smiles":"[B]=O","pubchemCid":"6327189","sourceIds":["PubChem CID 6327189"]},{"id":"aluminum-monoxide","name":"Aluminum monoxide","formula":"AlO","molecularWeight":42.98,"classification":"Diatomic molecule","category":"Reactive or high-temperature diatomic","smiles":"O=[Al]","pubchemCid":"142249","sourceIds":["PubChem CID 142249"]},{"id":"lithium-hydride","name":"Lithium hydride","formula":"LiH","molecularWeight":7.95,"classification":"Diatomic molecule (gas phase only)","category":"Ionic compound, a crystal lattice at room temperature","smiles":"[H-].[Li+]","pubchemCid":"62714","sourceIds":["PubChem CID 62714"],"notes":"Discrete LiH molecules exist in the vapor; the solid is an ionic crystal."},{"id":"lithium-fluoride","name":"Lithium fluoride","formula":"LiF","molecularWeight":25.94,"classification":"Diatomic molecule (gas phase only)","category":"Ionic compound, a crystal lattice at room temperature","smiles":"[Li+].[F-]","pubchemCid":"224478","sourceIds":["PubChem CID 224478"],"notes":"Discrete LiF molecules exist only in the vapor; the solid is an ionic crystal."},{"id":"lithium-chloride","name":"Lithium chloride","formula":"LiCl","molecularWeight":42.39,"classification":"Diatomic molecule (gas phase only)","category":"Ionic compound, a crystal lattice at room temperature","smiles":"[Li+].[Cl-]","pubchemCid":"433294","sourceIds":["PubChem CID 433294"],"notes":"Discrete LiCl molecules exist only in the vapor; the solid is an ionic crystal."},{"id":"sodium-fluoride","name":"Sodium fluoride","formula":"NaF","molecularWeight":41.99,"classification":"Diatomic molecule (gas phase only)","category":"Ionic compound, a crystal lattice at room temperature","smiles":"[F-].[Na+]","pubchemCid":"5235","sourceIds":["PubChem CID 5235"],"notes":"Discrete NaF molecules exist only in the vapor; the solid is an ionic crystal."},{"id":"sodium-chloride","name":"Sodium chloride","formula":"NaCl","molecularWeight":58.44,"classification":"Diatomic molecule (gas phase only)","category":"Ionic compound, a crystal lattice at room temperature","smiles":"[Na+].[Cl-]","pubchemCid":"5234","sourceIds":["PubChem CID 5234"],"notes":"Table salt. Discrete NaCl molecules exist only in the vapor; the solid is an ionic crystal."},{"id":"sodium-iodide","name":"Sodium iodide","formula":"NaI","molecularWeight":149.89,"classification":"Diatomic molecule (gas phase only)","category":"Ionic compound, a crystal lattice at room temperature","smiles":"[Na+].[I-]","pubchemCid":"5238","sourceIds":["PubChem CID 5238"],"notes":"Discrete NaI molecules exist only in the vapor; the solid is an ionic crystal."},{"id":"potassium-fluoride","name":"Potassium fluoride","formula":"KF","molecularWeight":58.1,"classification":"Diatomic molecule (gas phase only)","category":"Ionic compound, a crystal lattice at room temperature","smiles":"[F-].[K+]","pubchemCid":"522689","sourceIds":["PubChem CID 522689"],"notes":"Discrete KF molecules exist only in the vapor; the solid is an ionic crystal."},{"id":"potassium-chloride","name":"Potassium chloride","formula":"KCl","molecularWeight":74.55,"classification":"Diatomic molecule (gas phase only)","category":"Ionic compound, a crystal lattice at room temperature","smiles":"[Cl-].[K+]","pubchemCid":"4873","sourceIds":["PubChem CID 4873"],"notes":"Discrete KCl molecules exist only in the vapor; the solid is an ionic crystal."},{"id":"potassium-bromide","name":"Potassium bromide","formula":"KBr","molecularWeight":119,"classification":"Diatomic molecule (gas phase only)","category":"Ionic compound, a crystal lattice at room temperature","smiles":"[K+].[Br-]","pubchemCid":"253877","sourceIds":["PubChem CID 253877"],"notes":"Discrete KBr molecules exist only in the vapor; the solid is an ionic crystal."}]}