This guide records data provenance and the rules actually used by the UI. Citing an institution does not mean that it has endorsed every legacy value or classification.
Reviewed: 2026-09-08
Field sources, units and conditions
Unrecorded or unverified values are null (no data), not zero, and excluded from comparison calculations.
Field sources, units and conditions
Field
Definition / conditions
Source / status
Relative atomic mass / mass number
Dimensionless; legacy rounding retained. Parentheses denote mass numbers, not standard atomic weights. CIAAW intervals and uncertainties are not included; values are not a full update to the current CIAAW table.
°C; pressure and allotrope conditions are not fully documented. As has melting > boiling; check sublimation and pressure. The slider is a threshold model; logarithmic plots convert to K (°C+273.15).
ppm; BGS data in RSC’s Supply risk section. RSC’s glossary describes atoms per million crustal atoms. No independent conversion to mass ppm or mixing with other abundance tables.
Configuration, block, oxidation states, discovery year
RSC neutral-atom configuration, common oxidation states and year. Full configurations expand noble-gas cores. Elements 104–118 are conservatively labelled predicted in this resource, not certified measurements of all fields.
Shell totals sum occupations with the same n. Valence uses outer-shell counts for s/p, zero for noble gases by school convention, and is undefined here for d/f. Lewis dots use outer-shell counts. Diagrams are schematic, not trajectories or scale; arrows illustrate Hund’s rule.
Uses retain legacy Japanese text. Unverified origin, radioactivity and hazards are unrecorded in comparison data. Filter membership does not establish safety or biological essentiality.
Legacy numbers, symbols, four-language names, groups and periods are retained. Unassigned groups are null, not group zero. Identity and position are distinct from physical properties and filter categories.
Legacy table values are retained in legacyTable. Radius definitions, density conditions, rounding and allotropes may differ from RSC views. Existing detail text and images need individual provenance review; RSC is not their blanket source.
Classification rules and current members
Membership in the list below is the implemented test. Original selection documents are unverified; these lists are not guaranteed institutional classifications.
Cell colours and comparison categories use the shared category field; filters use separate lists. These can differ, notably for superheavy elements.
The ✧ marker is a legacy display flag, not a reassessment of origin, and can differ from natural/synthetic filter membership.
Alkali Metal — 6
Basic categories use legacy teaching lists. Group descriptions (1 excluding H, 2, 17, 18) do not determine inclusion of uncertain superheavy elements. Lanthanides are 57–71; actinides 89–103.
Basic categories use legacy teaching lists. Group descriptions (1 excluding H, 2, 17, 18) do not determine inclusion of uncertain superheavy elements. Lanthanides are 57–71; actinides 89–103.
IUPAC uses an incomplete d subshell in the atom or a resulting cation. This site’s broader teaching list includes Zn and Cd and is not a strict implementation of that definition.
Current membership: Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Rf, Db, Sg, Bh, Hs, Cn
Post-transition — 10
Basic categories use legacy teaching lists. Group descriptions (1 excluding H, 2, 17, 18) do not determine inclusion of uncertain superheavy elements. Lanthanides are 57–71; actinides 89–103.
Current membership: Al, Ga, In, Sn, Tl, Pb, Bi, Nh, Fl, Mc
Metalloid — 7
Basic categories use legacy teaching lists. Group descriptions (1 excluding H, 2, 17, 18) do not determine inclusion of uncertain superheavy elements. Lanthanides are 57–71; actinides 89–103.
Basic categories use legacy teaching lists. Group descriptions (1 excluding H, 2, 17, 18) do not determine inclusion of uncertain superheavy elements. Lanthanides are 57–71; actinides 89–103.
Basic categories use legacy teaching lists. Group descriptions (1 excluding H, 2, 17, 18) do not determine inclusion of uncertain superheavy elements. Lanthanides are 57–71; actinides 89–103.
Basic categories use legacy teaching lists. Group descriptions (1 excluding H, 2, 17, 18) do not determine inclusion of uncertain superheavy elements. Lanthanides are 57–71; actinides 89–103.
Basic categories use legacy teaching lists. Group descriptions (1 excluding H, 2, 17, 18) do not determine inclusion of uncertain superheavy elements. Lanthanides are 57–71; actinides 89–103.
Current membership: La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu
Actinide — 15
Basic categories use legacy teaching lists. Group descriptions (1 excluding H, 2, 17, 18) do not determine inclusion of uncertain superheavy elements. Lanthanides are 57–71; actinides 89–103.
Current membership: Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr
Unknown — 9
Basic categories use legacy teaching lists. Group descriptions (1 excluding H, 2, 17, 18) do not determine inclusion of uncertain superheavy elements. Lanthanides are 57–71; actinides 89–103.
Current membership: Mt, Ds, Rg, Nh, Fl, Mc, Lv, Ts, Og
Metal — 84
Metal/nonmetal/metalloid boundaries depend on references and properties. These lists are not an exhaustive, mutually exclusive partition of all 118 elements.
Current membership: Li, Be, Na, Mg, Al, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Fr, Ra, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr, Rf, Db, Sg, Bh, Hs, Cn
Nonmetal — 17
Metal/nonmetal/metalloid boundaries depend on references and properties. These lists are not an exhaustive, mutually exclusive partition of all 118 elements.
Current membership: H, He, C, N, O, F, Ne, P, S, Cl, Ar, Se, Br, Kr, I, Xe, Rn
Metalloid — 7
Metal/nonmetal/metalloid boundaries depend on references and properties. These lists are not an exhaustive, mutually exclusive partition of all 118 elements.
Current membership: B, Si, Ge, As, Sb, Te, Po
Unknown — 3
Metal/nonmetal/metalloid boundaries depend on references and properties. These lists are not an exhaustive, mutually exclusive partition of all 118 elements.
Current membership: Mt, Ds, Rg
Rare Metal — 32
Japan’s policy category of 31 mineral groups is not the same counting unit as this elemental list. The legacy list includes Fr and Ra; agreement with the official list is unverified.
Having no stable isotopes differs from having some radioactive isotopes. The legacy list omits Bi, unlike RSC’s Bi-209 radioactivity data. Do not use it as a complete stability test.
Current membership: Tc, Pm, Po, At, Rn, Fr, Ra, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, Cn, Nh, Fl, Mc, Lv, Ts, Og
Synthetic — 35
Laboratory synthesis and trace natural occurrence can coexist. The site’s legacy criteria are not resolved and its lists overlap; they are not exclusive origin categories.
Current membership: Tc, Pm, Po, At, Rn, Fr, Ra, Ac, Pa, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, Cn, Nh, Fl, Mc, Lv, Ts, Og
Natural — 90
Laboratory synthesis and trace natural occurrence can coexist. The site’s legacy criteria are not resolved and its lists overlap; they are not exclusive origin categories.
Current membership: H, He, Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Br, Kr, Rb, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, I, Xe, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Po, Rn, Ra, Ac, Th, Pa, U, Np, Pu
Magnetic — 4
Property filters use membership lists. Magnetism, superconductivity and semiconductor behaviour depend on temperature, pressure, crystal structure and allotrope; inclusion does not imply ambient-condition behaviour.
Current membership: Fe, Co, Ni, Gd
Superconductor — 29
Property filters use membership lists. Magnetism, superconductivity and semiconductor behaviour depend on temperature, pressure, crystal structure and allotrope; inclusion does not imply ambient-condition behaviour.
Current membership: Li, Be, Al, Ti, V, Zn, Ga, Zr, Nb, Mo, Tc, Ru, Rh, Cd, In, Sn, La, Hf, Ta, W, Re, Os, Ir, Pt, Hg, Tl, Pb, Th, U
Semiconductor — 6
Property filters use membership lists. Magnetism, superconductivity and semiconductor behaviour depend on temperature, pressure, crystal structure and allotrope; inclusion does not imply ambient-condition behaviour.
Current membership: B, C, Si, Ge, As, Te
Major Essential — 6
Organism, chemical species, required amounts and deficiency evidence are not standardized across these lists. The six major elements mean the CHNOPS teaching group, not all essential nutrients.
The legacy trace-essential list includes Na, K, Ca, Mg and Cr. It does not match standard macro/trace mineral grouping; assessments of Cr essentiality also differ (NIH ODS).
Current membership: Na, Mg, K, Ca, Fe, Zn, Cu, Mn, Se, I, Mo, Co, Cr, Cl, F
Possibly Essential — 7
“Possible” is a legacy teaching label, not proof of human essentiality. Organisms and supporting references have not been verified for each member.
Current membership: B, Si, V, Ni, As, Sn, Bi
Toxic — 17
Toxicity depends on species, oxidation state, dose and exposure route. Unselected does not mean safe; this list is not a GHS classification or SDS. Consult the actual chemical’s SDS and official GHS information.
Current membership: As, Cd, Hg, Pb, Po, Rn, Ra, Be, Tl, Ba, U, Pu, Br, F, Cl, N, O
Solid — 90
Filters use fixed lists intended for 25°C; comparison uses RSC at 20°C; the temperature slider uses legacy melting/boiling thresholds. Superheavy states and phase conditions include uncertainties.
Current membership: Li, Be, B, C, Na, Mg, Al, Si, P, S, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, I, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Tl, Pb, Bi, Po, At, Fr, Ra, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr
Liquid — 2
Filters use fixed lists intended for 25°C; comparison uses RSC at 20°C; the temperature slider uses legacy melting/boiling thresholds. Superheavy states and phase conditions include uncertainties.
Current membership: Br, Hg
Gas — 11
Filters use fixed lists intended for 25°C; comparison uses RSC at 20°C; the temperature slider uses legacy melting/boiling thresholds. Superheavy states and phase conditions include uncertainties.
Current membership: H, He, N, O, F, Ne, Cl, Ar, Kr, Xe, Rn
Unknown — 15
Filters use fixed lists intended for 25°C; comparison uses RSC at 20°C; the temperature slider uses legacy melting/boiling thresholds. Superheavy states and phase conditions include uncertainties.
Current membership: Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, Cn, Nh, Fl, Mc, Lv, Ts, Og
Automatically extracted counts and differences
In both natural and synthetic lists: Po, Rn, Ra, Ac, Pa, Np, Pu
Post-transition — Filter / cell-category symmetric difference: Nh, Fl, Mc
Noble Gas — Filter / cell-category symmetric difference: Og
Viewing trends
Viewing rankings aggregate this site’s view records, not physical properties or scientific importance. Category aggregation follows legacy metadata lists.