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Created November 1, 2025 22:35
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Chemical elements
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README.md

David Madore proposes three criteria for which elements really exist as chemical elements. I try to evaluate them for all elements.

I made this while sick as a dog, so there's probably mistakes.

Sources for all elements:

  • Half-lives and uncertainties: NuDat
  • Melting point measurements: got lazy and blindly trusted Wikipedia, sue me

Sources for individual elements are listed in the table.

Many sources give measurements in activity rather than mass. Conversion used:

from math import log

g_per_u = 1.660e-24
Bq_per_Ci = 3.7e10
def get_mass_from_activity(atomic_mass_in_u, half_life_in_s, activity_in_Bq):
  decay_param = log(2) / half_life_in_s
  nb_atoms = activity_in_Bq / decay_param
  atomic_mass_in_g = atomic_mass_in_u * g_per_u
  mass_in_g = atomic_mass_in_g * nb_atoms
  return mass_in_g

# Example: astatine-211
print(get_mass_from_activity(211, 25970, 6.6e9) * 1e9, 'ng')

# Example: actinium-225
print(get_mass_from_activity(225, 9.919 * 24 * 3600, 4. * Bq_per_Ci) * 1e6, 'µg')
Raw
elements.tsv
Name Z Stablest known isotope Half-life (NuDat) Half-life (min) Half-life (max) Half-life notes Naturally occurring on Earth Produced sample Sample source Criterion 1: Half-life longer than neutron? Criterion 2: Planck mass produced? Criterion 3: Melting/boiling point measured? TRUE element (fact-checked by real Americium patriots)?
Hydrogen 1 1H, 2H Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Helium 2 3He, 4He Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Lithium 3 6Li, 7Li Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Beryllium 4 9Be Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Boron 5 10B, 11B Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Carbon 6 12C, 13C Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Nitrogen 7 14N, 15N Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Oxygen 8 16O, 17O, 18O Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Fluorine 9 19F Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Neon 10 20Ne, 21Ne, 22Ne Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Sodium 11 23Na Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Magnesium 12 24Mg, 25Mg, 26Mg Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Aluminium 13 27Al Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Silicon 14 28Si, 29Si, 30Si Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Phosphorus 15 31P Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Sulfur 16 32S, 33S, 34S, 36S Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Chlorine 17 35Cl, 37Cl Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Argon 18 38Ar, 40Ar Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Potassium 19 39K, 41K Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Calcium 20 42Ca, 43Ca, 44Ca Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Scandium 21 45Sc Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Titanium 22 46Ti, 47Ti, 48Ti, 49Ti, 50Ti Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Vanadium 23 51V Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Chromium 24 52Cr, 53Cr, 54Cr Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Manganese 25 55Mn Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Iron 26 56Fe, 57Fe, 58Fe Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Cobalt 27 59Co Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Nickel 28 60Ni, 61Ni, 62Ni, 64Ni Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Copper 29 63Cu, 65Cu Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Zinc 30 66Zn, 67Zn, 68Zn Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Gallium 31 69Ga, 71Ga Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Germanium 32 70Ge, 72Ge, 73Ge, 74Ge Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Arsenic 33 75As Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Selenium 34 76Se, 77Se, 78Se Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Bromine 35 79Br, 81Br Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Krypton 36 80Kr, 82Kr, 83Kr, 84Kr Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Rubidium 37 85Rb Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Strontium 38 86Sr, 87Sr, 88Sr Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Yttrium 39 89Y Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Zirconium 40 90Zr, 91Zr, 92Zr Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Niobium 41 93Nb Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Molybdenum 42 94Mo, 95Mo, 96Mo, 97Mo Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Technetium 43 97Tc or 98Tc 4.2 million years 3.9 million years 4.5 million years Both isotopes' half-lives are estimated at 4.2 million years. Uncertainties are given for 98Tc (±0.3 million years, vs ±0.16 for 97Tc). Yes Macroscopic Yes Yes Yes Real chemical element
Ruthenium 44 98Ru, 99Ru, 100Ru, 101Ru, 102Ru Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Rhodium 45 103Rh Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Palladium 46 104Pd, 105Pd, 106Pd, 108Pd Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Silver 47 107Ag, 109Ag Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Cadmium 48 110Cd, 111Cd, 112Cd Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Indium 49 113In Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Tin 50 114Sn, 115Sn, 116Sn, 117Sn, 118Sn, 119Sn, 120Sn Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Antimony 51 121Sb, 123Sb Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Tellurium 52 122Te, 124Te, 125Te, 126Te Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Iodine 53 127I Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Xenon 54 128Xe, 129Xe, 130Xe, 131Xe, 132Xe Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Caesium 55 133Cs Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Barium 56 134Ba, 135Ba, 136Ba, 137Ba, 138Ba Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Lanthanum 57 139La Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Cerium 58 140Ce Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Praseodymium 59 141Pr Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Neodymium 60 142Nd Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Promethium 61 145Pm 17.7 years 17.3 years 18.1 years Yes: hundreds of grams (147Pm) 1 milligram 147Pm https://www.osti.gov/servlets/purl/1819632 Yes Yes Yes Real chemical element
Samarium 62 144Sm, 149Sm, 150Sm, 152Sm, 154Sm Stable (obs.) Stable (obs.) Stable (obs.) Yes Macroscopic Yes Yes Yes Real chemical element
Europium 63 153Eu Stable (obs.) Stable (obs.) Stable (obs.) Yes Macroscopic Yes Yes Yes Real chemical element
Gadolinium 64 156Gd, 157Gd, 158Gd Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Terbium 65 159Tb Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Dysprosium 66 163Dy, 164Dy Stable Stable Stable Yes Macroscopic Yes Yes Yes Real chemical element
Holmium 67 165Ho Stable (obs.) Stable (obs.) Stable (obs.) Yes Macroscopic Yes Yes Yes Real chemical element
Erbium 68 162Er, 164Er, 166Er, 167Er, 168Er, 170Er Stable (obs.) Stable (obs.) Stable (obs.) Yes Macroscopic Yes Yes Yes Real chemical element
Thulium 69 169Tm Stable (obs.) Stable (obs.) Stable (obs.) Yes Macroscopic Yes Yes Yes Real chemical element
Ytterbium 70 168Yb, 170Yb, 171Yb, 172Yb, 173Yb, 174Yb, 176Yb Stable (obs.) Stable (obs.) Stable (obs.) Yes Macroscopic Yes Yes Yes Real chemical element
Lutetium 71 175Lu Stable (obs.) Stable (obs.) Stable (obs.) Yes Macroscopic Yes Yes Yes Real chemical element
Hafnium 72 176Hf, 177Hf, 178Hf, 179Hf, 180Hf Stable (obs.) Stable (obs.) Stable (obs.) Yes Macroscopic Yes Yes Yes Real chemical element
Tantalum 73 180mTa, 181Ta Stable (obs.) Stable (obs.) Stable (obs.) Yes Macroscopic Yes Yes Yes Real chemical element
Tungsten 74 182W, 183W, 184W, 186W Stable (obs.) Stable (obs.) Stable (obs.) Yes Macroscopic Yes Yes Yes Real chemical element
Rhenium 75 185Re Stable (obs.) Stable (obs.) Stable (obs.) Yes Macroscopic Yes Yes Yes Real chemical element
Osmium 76 187Os, 188Os, 189Os, 190Os, 192Os Stable (obs.) Stable (obs.) Stable (obs.) Yes Macroscopic Yes Yes Yes Real chemical element
Iridium 77 191Ir, 193Ir Stable (obs.) Stable (obs.) Stable (obs.) Yes Macroscopic Yes Yes Yes Real chemical element
Platinum 78 192Pt, 194Pt, 195Pt, 196Pt, 198Pt Stable (obs.) Stable (obs.) Stable (obs.) Yes Macroscopic Yes Yes Yes Real chemical element
Gold 79 197Au Stable (obs.) Stable (obs.) Stable (obs.) Yes Macroscopic Yes Yes Yes Real chemical element
Mercury 80 196Hg, 198Hg, 199Hg, 200Hg, 201Hg, 202Hg, 204Hg Stable (obs.) Stable (obs.) Stable (obs.) Yes Macroscopic Yes Yes Yes Real chemical element
Thallium 81 203Tl, 205Tl Stable (obs.) Stable (obs.) Stable (obs.) Yes Macroscopic Yes Yes Yes Real chemical element
Lead 82 204Pb, 206Pb, 207Pb, 208Pb Stable (obs.) Stable (obs.) Stable (obs.) Yes Macroscopic Yes Yes Yes Real chemical element
Bismuth 83 209Bi 20 quintillion years 20 quintillion years 20 quintillion years Yes Macroscopic Yes Yes Yes Real chemical element
Polonium 84 209Po 124 years 121 years 127 years Yes 1–10 milligrams 210Po https://doi.org/10.1016/j.jenvrad.2023.107259 Yes Yes Yes Real chemical element
Astatine 85 210At 8.1 hours 7.7 hours 8.5 hours Yes: hundreds of milligrams to tens of grams. (215At, 217At, 218At, 219At) 120 nanograms 211At https://www.osti.gov/servlets/purl/1853514 Yes Not in one place Yes On thin ice
Radon 86 222Rn 3.8 days 3.8 days 3.8 days Yes 856 nanograms 222Rn https://doi.org/10.1039%2FCT9099501073 Yes If you count a uranium mine as a big sample… Yes On thin ice
Francium 87 223Fr 22.0 minutes 22.0 minutes 22.0 minutes Yes: tens of grams. (223Fr) 80 attograms (2e5 atoms) 209Fr https://arxiv.org/pdf/1312.3562 Yes Not in one place Yes On thin ice
Radium 88 226Ra 1.6 thousand years 1.6 thousand years 1.6 thousand years Yes Macroscopic Yes Yes Yes Real chemical element
Actinium 89 227Ac 22 years 22 years 22 years Yes: tens of grams. (225Ac) 68 micrograms 225Ac https://arxiv.org/pdf/2101.00291 Yes Yes Yes Real chemical element
Thorium 90 232Th 14 billion years 14 billion years 14 billion years Yes Macroscopic Yes Yes Yes Real chemical element
Protactinium 91 231Pa 33 thousand years 33 thousand years 33 thousand years Yes Macroscopic https://periodic.lanl.gov/91.shtml Yes Yes Yes Real chemical element
Uranium 92 238U 4.5 billion years 4.5 billion years 4.5 billion years Yes Macroscopic Yes Yes Yes Real chemical element
Neptunium 93 237Np 2.1 million years 2.1 million years 2.1 million years Yes Macroscopic Yes Yes Yes Real chemical element
Plutonium 94 244Pu 81 million years 81 million years 81 million years Yes Macroscopic Yes Yes Yes Real chemical element
Americium 95 243Am 7.3 thousand years 7.3 thousand years 7.3 thousand years Unconfirmed Macroscopic https://periodic.lanl.gov/95.shtml Yes Yes Yes Real chemical element
Curium 96 247Cm 16 million years 16 million years 16 million years Unconfirmed Macroscopic https://periodic.lanl.gov/96.shtml Yes Yes Yes Real chemical element
Berkelium 97 247Bk 1.4 thousand years 1.1 thousand years 1.6 thousand years No 22.2 milligrams 249Bk https://sci-hub.in/10.1103/PhysRevLett.104.142502 Yes Yes Yes Real chemical element
Californium 98 251Cf 898 years 855 years 941 years No 10 milligrams https://periodic.lanl.gov/98.shtml Yes Yes Yes (melting only) Real chemical element
Einsteinium 99 252Es 1.3 years 1.3 years 1.3 years No 2 milligrams https://periodic.lanl.gov/99.shtml Yes Yes Yes (melting only) Real chemical element
Fermium 100 257Fm 100 days 100 days 100 days No 1.7 nanograms (2.7e10 atoms) 255Fm https://www.sci-hub.in/10.1103/PhysRevLett.90.163002 Yes No No Mental illness
Mendelevium 101 258Md 52 days 52 days 52 days No 0.4 femtograms (1e6 atoms) 256Md https://web.archive.org/web/20100717155410/http://radchem.nevada.edu/classes/rdch710/files/Fm%20to%20Lr.pdf p.1631 Yes No No Mental illness
Nobelium 102 259No 58 minutes 55 minutes 63 minutes No 0.5 attograms (1200 atoms) 255No https://web.archive.org/web/20100717155410/http://radchem.nevada.edu/classes/rdch710/files/Fm%20to%20Lr.pdf p.1638 Yes No No Mental illness
Lawrencium 103 266Lr 11 hours 6 hours 32 hours No 0.7 attograms (1500 atoms) 256Lr https://web.archive.org/web/20100717155410/http://radchem.nevada.edu/classes/rdch710/files/Fm%20to%20Lr.pdf p.1645 Yes No No Mental illness
Rutherfordium 104 267Rf 1.3 hours 0.6 hours 3.6 hours Oganessian et al (Aug 2022) find 0.8 hours (min 0.6 hours, max 1.2 hours) https://indico.jinr.ru/event/3339/attachments/13778/22977/Ref1%20114%20112%20PRC.106.024612.pdf No Single atoms https://web.archive.org/web/20080528125634/http://wwwsoc.nii.ac.jp/jnrs/paper/JN62/jn6202.pdf Yes No No Mental illness
Dubnium 105 268Db 26 hours 24 hours 29 hours Oganessian et al (Sep 2022) find 16 hours (min 12 hours, max 22 hours) https://harvest.aps.org/v2/journals/articles/10.1103/PhysRevC.106.L031301/fulltext No Single atoms Yes No No Mental illness
Seaborgium 106 269Sg or 267Sg 2.13 minutes (269Sg) 1.16 minutes 12.35 minutes Kovrizhnykh (2025) finds 14 minutes (min 11 minutes, max 23 minutes) for 269Sg https://indico.gsi.de/event/21160/contributions/85071/attachments/49852/75915/TASCA25_Contribution_Kovrizhnykh.pdf No Single atoms https://www.sci-hub.in/10.1126/science.1255720 Probably not No No Mental illness
Bohrium 107 278Bh 19 minutes 14 minutes 74 minutes Hofmann et al (2016) find 11.5 minutes (min 6.3 minutes, max 67 minutes) https://www.sci-hub.in/10.1140/epja/i2016-16180-4 No Single atoms Probably No No Mental illness
Hassium 108 269Hs 13 seconds 9 seconds 23 seconds 271Hs may be stabler (46s?), or the excited isomer 277mHs (30–130s?), but not in NuDat yet. No Single atoms No No No Mental illness
Meitnerium 109 278Mt 4.5 seconds 3.2 seconds 8.0 seconds Hofmann et al (2016) find that 282Mt may be much stabler: 1 minute (min 0.6 minutes, max 6.4 minutes) https://www.sci-hub.in/10.1140/epja/i2016-16180-4 No Single atoms No No No Mental illness
Darmstadtium 110 282Ds 1 minute 0.6 minutes 6.4 minutes Unconfirmed. Next stablest is 281Ds at 12 seconds (min 10 seconds, max 16 seconds). No Single atoms No No No Mental illness
Roentgenium 111 282Rg 1.7 minutes 1.2 minutes 2.8 minutes Hofmann et al (2016) find that 286Rg may be much stabler: 11 minutes (min 6 minutes, max 62 minutes) https://www.sci-hub.in/10.1140/epja/i2016-16180-4 No Single atoms Probably not No No Mental illness
Copernicium 112 286Cn 11 minutes 6 minutes 62 minutes Unconfirmed. Next stablest is 285Cn at 33 seconds (min 27 seconds, max 43 seconds). No Single atoms Maybe No No Mental illness
Nihonium 113 286Nh 9.5 seconds 6.8 seconds 16 seconds No Single atoms No No No Mental illness
Flerovium 114 290Fl 19 seconds 10 seconds 110 seconds Unconfirmed. Next stablest is 289Fl at 2.4 seconds (min 1.9 seconds, max 3.2 seconds). No Single atoms No No No Mental illness
Moscovium 115 290Mc 0.65 seconds 0.45 seconds 1.1 seconds No Single atoms No No No Mental illness
Livermorium 116 293Lv 95 milliseconds 68 milliseconds 158 milliseconds Oganessian et al (2015) find 57 ms (min 40 ms, max 100 ms) https://doi.org/10.1088/0034-4885/78/3/036301 No Single atoms No No No Mental illness
Tennessine 117 294Ts 51 milliseconds 35 milliseconds 89 milliseconds No Single atoms No No No Mental illness
Oganesson 118 294Og 0.58 milliseconds 0.40 milliseconds 1.0 millisecond No Single atoms No No No Mental illness
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