Paradigmatic instances of chemical elements — hydrogen, carbon, nitrogen, oxygen, iron, gold, and the noble-gas group — each an `instance_of` the periodic table. Exercises the elemental-instance level of the ontology and provides the…
elements
Hydrogen (H, Z=1)
Simplest and most abundant chemical element (Z=1). One proton + one electron in its neutral atom. Gaseous H₂ at STP; central role in the…
Carbon (C, Z=6)
Element with Z=6 forming the backbone of organic chemistry and life. Allotropes include diamond, graphite, fullerenes, and graphene. Its…
Nitrogen (N, Z=7)
Element with Z=7. Molecular N₂ makes up ~78 % of Earth's atmosphere and is chemically inert under ordinary conditions owing to the triple…
Oxygen (O, Z=8)
Element with Z=8. Second most electronegative element; ubiquitous as O₂ (~21 % of atmosphere) and in oxide/silicate minerals.…
Iron (Fe, Z=26)
Transition metal with Z=26. Most abundant heavy element by mass in Earth's core and crust; peak of the nuclear-binding-energy curve.…
Gold (Au, Z=79)
Noble transition metal with Z=79. Chemically inert under most conditions owing to relativistic-stabilised 6s electrons; also responsible…
Noble gases
Group-18 elements (He, Ne, Ar, Kr, Xe, Rn, Og) with full valence shells, very high ionisation energies, negligible electron affinities, and…
Helium (He, Z=2)
Second-lightest element; noble gas with closed 1s² shell. Second-most abundant element in the universe; used in cryogenics and lifting gas.
Lithium (Li, Z=3)
Lightest alkali metal (1s²2s¹). Central to modern Li-ion batteries and to lithium-salt psychiatric medicine.
Beryllium (Be, Z=4)
Alkaline-earth metal with high stiffness-to-weight ratio; toxic. Neutron-moderator material in some reactor designs.
Boron (B, Z=5)
Metalloid with electron-deficient bonding patterns (e.g. boranes). Essential plant micronutrient; ¹⁰B used as neutron absorber.
Sodium (Na, Z=11)
Alkali metal; ubiquitous as Na⁺ in biology and in seawater (as NaCl). Central to neural action potentials in L3 physiology.
Magnesium (Mg, Z=12)
Alkaline-earth metal; essential biometal at the core of chlorophyll and in hundreds of enzymes.
Aluminium (Al, Z=13)
Most abundant metal in Earth's crust. Lightweight structural metal after surface-oxide passivation.
Silicon (Si, Z=14)
Second-most abundant element in Earth's crust (after O). Substrate of microelectronics; core of all silicate minerals.
Phosphorus (P, Z=15)
Essential biometal; backbone of DNA/RNA (phosphodiester), energy currency (ATP), and cell membranes (phospholipids).
Sulfur (S, Z=16)
Chalcogen; central to proteins (Cys/Met amino acids, disulfide bonds) and industrial chemistry (H₂SO₄).
Chlorine (Cl, Z=17)
Yellow-green halogen gas; Cl⁻ is a major biological anion; ClO⁻ used for disinfection.
Potassium (K, Z=19)
Alkali metal; K⁺ is the dominant intracellular cation and partners with Na⁺ in action potentials.
Calcium (Ca, Z=20)
Alkaline-earth metal; structural (bones, shells) and signalling (Ca²⁺ is a universal second messenger).
Copper (Cu, Z=29)
Transition metal; excellent electrical and thermal conductor. Redox-active biometal in cytochrome c oxidase.
Zinc (Zn, Z=30)
Transition metal; essential cofactor in ~10% of enzymes (zinc-finger transcription factors, carbonic anhydrase).
Silver (Ag, Z=47)
Noble transition metal with highest electrical conductivity of any element; antimicrobial.
Mercury (Hg, Z=80)
Only metal liquid at standard conditions (relativistic contraction of 6s orbital weakens metallic bonding). Toxic; historic use in…
Fluorine (F, Z=9)
Most electronegative element; pale-yellow diatomic gas F₂. Forms the strongest single bonds to carbon (C–F). Key industrial elements:…
Neon (Ne, Z=10)
Noble gas; inert closed-shell [He]2s²2p⁶. Used in discharge-tube signage and as cryogenic coolant.
Argon (Ar, Z=18)
Most abundant noble gas in Earth's atmosphere (~0.93 %). Inert shielding gas for welding and crystal growth.
Scandium (Sc, Z=21)
Light transition metal; aerospace-grade Al-Sc alloys.
Titanium (Ti, Z=22)
Strong, corrosion-resistant, biocompatible transition metal. Used in aerospace alloys, implants, and TiO₂ pigment.
Vanadium (V, Z=23)
Hard transition metal used as steel alloying agent and in V₂O₅ catalyst for H₂SO₄ production.
Chromium (Cr, Z=24)
Transition metal; passivating surface layer makes stainless steel corrosion-resistant. Cr(VI) is carcinogenic.
Manganese (Mn, Z=25)
Transition metal essential in steel making and in biology (photosystem II Mn₄CaO₅ cluster splits water).
Cobalt (Co, Z=27)
Ferromagnetic transition metal; central atom of vitamin B₁₂; critical material for Li-ion battery cathodes.
Nickel (Ni, Z=28)
Ferromagnetic transition metal; core constituent of stainless steel and of Earth's inner core.
Gallium (Ga, Z=31)
Post-transition metal that melts at 29.76 °C (in the hand). GaAs and GaN semiconductors power LEDs and high-frequency electronics.
Germanium (Ge, Z=32)
Metalloid semiconductor; first transistor material (1947). Now used in fiber-optics and infrared optics.
Arsenic (As, Z=33)
Toxic metalloid; historically used in pigments and as a poison. n-type dopant in Si/Ge semiconductors.
Selenium (Se, Z=34)
Non-metal chalcogen; essential trace element (selenocysteine, the 21st amino acid). Photoconductor used in xerography.
Bromine (Br, Z=35)
Red-brown liquid halogen at STP; only non-metal liquid at room temperature alongside Hg among metals. Flame-retardants, pharmaceuticals.
Krypton (Kr, Z=36)
Heavy noble gas; used in specialty lighting and as the historical meter-definition standard (1960–1983).
Rubidium (Rb, Z=37)
Alkali metal; Rb atomic clocks and Bose-Einstein-condensate work use its optical-cooling transitions.
Strontium (Sr, Z=38)
Alkaline-earth metal; ⁹⁰Sr is a notorious fission product (bone-seeking). Red-flame colour in pyrotechnics.
Yttrium (Y, Z=39)
Transition metal; Y₂O₃ in YAG lasers and in YBCO high-Tc superconductor.
Zirconium (Zr, Z=40)
Transition metal; low neutron-absorption cross-section makes Zircaloy the standard fuel-rod cladding in nuclear reactors.
Niobium (Nb, Z=41)
Transition metal; Nb₃Sn and Nb-Ti are workhorse superconductors for MRI and particle-accelerator magnets.
Molybdenum (Mo, Z=42)
Refractory transition metal; essential in nitrogenase (Mo-Fe cluster) and in high-temperature alloys.
Technetium (Tc, Z=43)
First synthetic element (1937). No stable isotopes; ⁹⁹ᵐTc is the dominant radiotracer in nuclear medicine.
Ruthenium (Ru, Z=44)
Platinum-group metal; key catalyst in olefin metathesis (Grubbs catalyst) and in industrial NH₃ oxidation.
Rhodium (Rh, Z=45)
Platinum-group metal; principal NOx-reduction component of automotive three-way catalytic converters.
Palladium (Pd, Z=46)
Platinum-group metal; central catalyst in C–C coupling reactions (Heck, Suzuki, Negishi) and in H₂ storage.
Cadmium (Cd, Z=48)
Soft toxic transition metal; historical NiCd batteries and CdTe photovoltaics.
Indium (In, Z=49)
Soft post-transition metal; indium-tin oxide (ITO) is the dominant transparent conductor for touchscreens and displays.
Tin (Sn, Z=50)
Post-transition metal with magic neutron number implications for nuclear stability. Alloys: bronze, solder, pewter.
Antimony (Sb, Z=51)
Metalloid; used in flame retardants, lead-acid battery alloys, and historically in cosmetics (kohl).
Tellurium (Te, Z=52)
Metalloid chalcogen; CdTe photovoltaics and phase-change memory (Ge-Sb-Te alloys).
Iodine (I, Z=53)
Halogen; essential in thyroid hormone synthesis (T₃, T₄). Antiseptic; radiocontrast media.
Xenon (Xe, Z=54)
Heaviest stable noble gas; forms a small but real chemistry (XeF₂, XeF₄, XeO₃). Anaesthetic and ion-thruster propellant.
Caesium (Cs, Z=55)
Alkali metal; the SI second is defined via the hyperfine transition of ¹³³Cs (9 192 631 770 Hz).
Barium (Ba, Z=56)
Alkaline-earth metal; BaSO₄ is an X-ray contrast agent; Ba²⁺ is toxic (K⁺-channel blocker).
Lanthanum (La, Z=57)
First lanthanide; LaNi₅ for hydride storage and in NiMH batteries.
Cerium (Ce, Z=58)
Most abundant lanthanide; CeO₂ is a three-way catalyst oxygen-buffer. Redox-active Ce(III)/Ce(IV).
Praseodymium (Pr, Z=59)
Lanthanide; magnet alloys and glass/ceramic colourants.
Neodymium (Nd, Z=60)
Lanthanide; Nd₂Fe₁₄B permanent magnets are the strongest commercial magnets; Nd:YAG lasers.
Promethium (Pm, Z=61)
Only radioactive lanthanide with no stable isotope; historical luminous paints.
Samarium (Sm, Z=62)
Lanthanide; SmCo₅ high-temperature permanent magnets.
Europium (Eu, Z=63)
Lanthanide; red phosphor in CRT and fluorescent lamps (Eu³⁺); anti-counterfeiting in euro banknotes.
Gadolinium (Gd, Z=64)
Lanthanide with half-filled 4f⁷; strong paramagnet → MRI contrast agents; highest thermal-neutron-capture cross section of any stable…
Terbium (Tb, Z=65)
Lanthanide; green phosphor component in trichromatic lighting.
Dysprosium (Dy, Z=66)
Lanthanide; Dy-doped Nd₂Fe₁₄B magnets retain coercivity at high T (EV motors, wind turbines).
Holmium (Ho, Z=67)
Lanthanide; highest magnetic moment per atom (10.6 μ_B); Ho:YAG medical lasers.
Erbium (Er, Z=68)
Lanthanide; Er-doped fiber amplifiers (EDFA) underpin long-haul optical-fiber telecom.
Thulium (Tm, Z=69)
Least abundant naturally occurring lanthanide; Tm-doped fiber lasers at 2 μm.
Ytterbium (Yb, Z=70)
Lanthanide; Yb atomic lattice clocks give among the best known frequency stabilities.
Lutetium (Lu, Z=71)
Heaviest lanthanide; ¹⁷⁷Lu-DOTATATE used in radiopharmaceutical therapy of neuroendocrine tumors.
Hafnium (Hf, Z=72)
Transition metal; HfO₂ replaced SiO₂ as gate-dielectric in sub-45 nm CMOS (high-κ dielectric).
Tantalum (Ta, Z=73)
Refractory transition metal; Ta₂O₅ is the dielectric of high-capacitance tantalum capacitors; biocompatible implants.
Tungsten (W, Z=74)
Metal with highest melting point of any element (3422 °C); incandescent-lamp filaments; WC cutting tools.
Rhenium (Re, Z=75)
Last stable element discovered (1925); Re-Pt catalysts for petroleum reforming; superalloy additive for jet-engine turbine blades.
Osmium (Os, Z=76)
Densest naturally occurring element (22.59 g/cm³). Platinum-group metal.
Iridium (Ir, Z=77)
Platinum-group metal; anomalous worldwide K-Pg layer abundance is the Alvarez impact-extinction signature.
Platinum (Pt, Z=78)
Noble transition metal; Pt/Rh/Pd catalytic converters; cis-platin anticancer drug; historical standard of mass (Pt-Ir kilogram prototype).
Thallium (Tl, Z=81)
Soft toxic post-transition metal; 'the poisoner's poison'. Used in some infrared optics.
Lead (Pb, Z=82)
Heavy post-transition metal with magic proton number 82. Historical plumbing/paint/fuel uses; now recognized as a potent neurotoxin.…
Bismuth (Bi, Z=83)
Heaviest element whose common isotope was long thought stable (²⁰⁹Bi actually α-decays with t₁/₂ ≈ 2×10¹⁹ yr). Low-toxicity Pb replacement;…
Polonium (Po, Z=84)
Radioactive metalloid; ²¹⁰Po is an intense α-emitter used in anti-static brushes and infamously as a poison (Litvinenko).
Astatine (At, Z=85)
Rarest naturally occurring element; extremely radioactive halogen (longest t₁/₂ isotope ²¹⁰At ≈ 8.1 h).
Radon (Rn, Z=86)
Radioactive noble gas; second-leading cause of lung cancer after smoking. Daughter product of Ra decay chains in U-bearing rocks.
Francium (Fr, Z=87)
Heaviest alkali metal; all isotopes radioactive with t₁/₂ ≤ 22 min. Never isolated in bulk.
Radium (Ra, Z=88)
Radioactive alkaline-earth metal; historical luminous paint use caused the 'radium girls' tragedy.
Actinium (Ac, Z=89)
First actinide; ²²⁵Ac targeted α-therapy for cancer.
Thorium (Th, Z=90)
Weakly radioactive actinide (t₁/₂ ≈ 1.4×10¹⁰ yr for ²³²Th); fertile fuel for Th-U breeder reactors (molten-salt concepts).
Protactinium (Pa, Z=91)
Actinide; intermediate in ²³²Th → ²³³U breeder reactions.
Uranium (U, Z=92)
Heaviest primordial element; ²³⁵U is the only naturally fissile nuclide. Fuel of ~all fission reactors and of enriched-U fission weapons.
Neptunium (Np, Z=93)
First transuranic synthesized (1940). ²³⁷Np is long-lived (~2.14 Myr) and is the start of the only fully extinct primordial decay chain…
Plutonium (Pu, Z=94)
Actinide; ²³⁹Pu is fissile and the core isotope of most modern fission weapons and of MOX reactor fuel.
Americium (Am, Z=95)
Actinide; ²⁴¹Am α-source powers virtually all ionisation-chamber smoke detectors.
Curium (Cm, Z=96)
Actinide; used as α-source in radioisotope thermoelectric generators and in XRF analyzers on Mars rovers (Curiosity, Perseverance).
Berkelium (Bk, Z=97)
Actinide; used as target material for synthesis of element 117 (tennessine).
Californium (Cf, Z=98)
Actinide; ²⁵²Cf is a compact spontaneous-fission neutron source (well-logging, cancer therapy).
Einsteinium (Es, Z=99)
Actinide; first isolated from 1952 Ivy Mike thermonuclear test debris.
Fermium (Fm, Z=100)
Last actinide reachable by neutron bombardment; all isotopes radioactive.
Mendelevium (Md, Z=101)
First transfermium element; synthesized only atom-at-a-time.
Nobelium (No, Z=102)
Actinide; unusual stable +2 oxidation state due to filled 5f¹⁴ shell.
Lawrencium (Lr, Z=103)
Final actinide; relativistic effects place outer electron in 7p rather than 6d.
Rutherfordium (Rf, Z=104)
First transactinide; group-4 homologue of Hf. Chemistry confirmed atom-at-a-time.
Dubnium (Db, Z=105)
Transactinide; group-5 homologue of Ta.
Seaborgium (Sg, Z=106)
Transactinide; group-6 homologue of W. Named for Glenn Seaborg (while he was still alive — a rare honour).
Bohrium (Bh, Z=107)
Transactinide; group-7 homologue of Re.
Hassium (Hs, Z=108)
Transactinide; group-8 homologue of Os. HsO₄ volatility confirmed chemically.
Meitnerium (Mt, Z=109)
Transactinide; named for Lise Meitner.
Darmstadtium (Ds, Z=110)
Transactinide; named for GSI Darmstadt where it was discovered.
Roentgenium (Rg, Z=111)
Transactinide; group-11 homologue of Au. Predicted to show strong relativistic effects.
Copernicium (Cn, Z=112)
Transactinide; volatile, mercury-like metal. First produced 1996 at GSI.
Nihonium (Nh, Z=113)
Named for Japan (RIKEN synthesis, 2004). Officially added to periodic table in 2016.
Flerovium (Fl, Z=114)
Island-of-stability candidate (N=184); observed isotopes have t₁/₂ up to seconds.
Moscovium (Mc, Z=115)
Named for Moscow oblast (JINR Dubna synthesis).
Livermorium (Lv, Z=116)
Named for Lawrence Livermore National Laboratory.
Tennessine (Ts, Z=117)
Named for Tennessee (Oak Ridge National Laboratory). Heaviest halogen (group-17 homologue), though chemistry unconfirmed.
Oganesson (Og, Z=118)
Heaviest element on the periodic table. Predicted to be a solid (not a gas) at STP due to relativistic effects, despite being a group-18…
Element abundances (solar, crustal, human)
Solar: H 74%, He 24%, O 1%; Crustal: O 47%, Si 28%, Al 8%; Human: O 65%, C 18%, H 10%; biological essentiality.
Rare earths & critical minerals
Ln + Sc + Y used in magnets, phosphors, catalysts; China dominates supply; criticality analysis by DOE, EU.
Helium-3 supply and applications
Tritium decay product; neutron detection, NMR cryogenics, dilution refrigerators; scarcity from cutback in nuclear arsenals.
Lithium resources for batteries
Salars (Chile, Argentina, Bolivia), hard rock (Australia); Li-ion + solid-state demand driving 20%/yr growth.
Platinum-group metals (PGMs)
Ru, Rh, Pd, Os, Ir, Pt; autocatalysts, chemicals, fuel cells; South Africa + Russia supply; recycling increasingly important.
Cobalt supply chain & Co-free batteries
DRC dominance, ethical mining concerns; LFP (LiFePO₄) chemistry avoids Co; Ni-rich NMC reduces loading.
Synthesized superheavy elements (Rf–Og)
Z=104-118 synthesized at GSI, JINR, RIKEN; single-atom or few-atom quantities; decay by α, SF; next targets 119, 120.
Actinide fuel cycle elements (U, Th, Pu, Np, Am)
Uranium 0.72% U-235 natural; Pu-239 from n-capture; Th-232 fertile breeding; minor actinides in spent fuel.