transition metal
Enable an AI agent to identify a transition-metal element, assess its state in a particular material or chemical environment, and determine which uses or transformations have adequate supporting evidence.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
Researched by: Codex + Grok
Purpose and description
Enable an AI agent to identify a transition-metal element, assess its state in a particular material or chemical environment, and determine which uses or transformations have adequate supporting evidence.
A transition metal is a metallic d-block element whose atom has an incomplete d subshell, or which can form a cation with an incomplete d subshell, in practice the metals of groups 3-11.
It can be Classify a candidate element against a stated transition-metal definition and flag unresolved boundary cases.; Select analytical observations that distinguish elemental material from oxidized, coordinated or alloyed forms.; Compare metal candidates for a specified role using measurements obtained under compatible conditions.; Evaluate a proposed oxidation, reduction, coordination or surface-treatment step against evidence for the identified species and material form.; Detect when changed speciation, surface condition or impurities invalidate an earlier assessment.; Route a proposed use to the relevant compound, alloy, process and hazard models before treating it as supported..
Distinguishing features
Test for a partially occupied d subshell in the atom or a supported cation under the adopted definition; periodic-table position alone does not document that test. [IUPAC Gold Book: transition element](https://goldbook.iupac.org/terms/view/T06456)
Distinguish an element's class membership from the electron count of the particular species being examined; record both before deciding whether an observed species supports classification.
For disputed boundaries such as group 12, require an explicit classification convention and evidence for the qualifying electronic state rather than silently equating d-block and transition metal.
Distinguish elemental metal from a metal-containing salt, oxide, complex or alloy by recording chemical species and composition; detecting the element alone does not establish elemental material.
Treat colour, magnetic response, multiple oxidation states and catalytic activity as observations to explain, not sufficient standalone membership tests.
Scope
+ Elemental identity and evidence for membership in the transition-metal class under a named definition.
+ Electronic configurations of the neutral atom and relevant cations, distinguished from formal electron counts in compounds.
+ Observed oxidation states and local coordination environments in identified samples.
+ Elemental material form, purity, phase and surface condition relevant to interpreting measurements.
+ Evidence supporting redox, coordination, catalytic or material uses under specified conditions.
- Complete molecular structures, properties and reaction networks of individual transition-metal compounds and complexes.
- Full composition, processing history and engineering qualification of alloys and manufactured components.
- Detailed mineral, ore-deposit, mining and extraction-process models.
- Comprehensive models of lanthanoids, actinoids and other neighbouring element classes.
- Complete toxicological assessments, exposure-control procedures and waste-management rules.
Characteristics
- Element identity
- Element name, symbol and atomic number Anchors classification and prevents properties of different metals from being conflated.
- Transition-metal membership
- Included, excluded or unresolved under a named definition and cited evidence Makes classification boundaries explicit and reviewable.
- Electronic configuration
- Configuration and d-electron occupancy, with species, charge and electronic state Provides the electronic evidence needed for classification and chemical interpretation.
- Oxidation-state assignment
- Formal oxidation state or distribution, assignment method and uncertainty Supports assessment of redox changes without confusing formal oxidation state with measured atomic charge.
- Chemical host
- Linked elemental substance, compound, complex, alloy or mixed-phase sample Identifies which entity actually carries the observed properties.
- Coordination environment
- Ligand or neighbour identities, coordination number, geometry and evidence Connects local metal environments to observed behaviour without assigning one environment to the entire element.
- Element content and impurities
- Mass fraction or amount fraction, with analytical method and detection limits Separates nominal metal identity from the composition of the material being assessed.
- Material and surface condition
- Phase, bulk or dispersed form, particle-size description, surface composition and observation conditions Allows an agent to judge whether evidence transfers between bulk metal, powder, supported sites and altered surfaces.
- Redox potential
- V versus a named reference electrode, with redox couple, medium, temperature and measurement conditions Supports comparison of specific redox transformations under compatible conditions.
- Magnetic response
- Susceptibility or magnetic moment with explicit units, normalization, field and temperature Provides evidence for evaluating electronic-state interpretations and application requirements.
- Validated use
- Linked application or transformation, tested metal form, operating conditions and performance evidence Prevents a reported use of one metal species or formulation from becoming a blanket affordance of the element.
Also called
Where this came from
wikidata · CC0 1.0
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 6 bundles · 11 layers · 18 findings · 28 questions.
Element identity and classification Establish which element is represented and why it belongs within the adopted transition-metal boundary.
The registry has no recorded definition, so membership must be an explicit, evidenced decision.
Element identification
Separate elemental identity from sample labels and material composition.
Confirmed element identity
Record the element being assessed and the evidence connecting a material observation to that element.
- Which element name, symbol and atomic number does this record represent? definition
- Which analytical result or authoritative record establishes the element's identity, and does it establish chemical form as well? provenance
Membership boundary
Apply a declared convention and preserve disagreements at the edges of the class.
Electronic membership evidence
Connect the classification decision to the qualifying atomic or cationic electronic state.
- Which transition-metal definition is being applied, and which atomic or cationic configuration satisfies it? definition
- Would another relevant convention change membership, particularly for group 3, group 12 or elements discussed as inner transition elements? boundary
Electronic state and speciation Represent the metal's actual chemical environment separately from element-level classification.
An agent needs species-specific evidence to interpret metal behaviour and assess possible transformations.
Oxidation and electron count
Distinguish oxidation-state assignments, formal d counts and measured electronic evidence.
Supported electronic assignment
Record the electronic assignment for the observed species, including mixed or unresolved states.
- Which oxidation states and formal d-electron counts are assigned to the metal species present? definition
- Which measurements support these assignments, and can they distinguish mixed valence or alternative interpretations? measurement
Local coordination
Identify the metal's neighbours and connect local environments to separately modelled chemical species.
Resolved metal environment
Record coordination evidence without treating a compound's complete structure as a property of the element.
- Which ligands or neighbouring atoms, coordination numbers and geometries are supported for the metal sites? measurement
- Which compound, complex or solid-phase model owns each environment, and are multiple environments unresolved? boundary
Material form and surface Establish what metal-bearing material is present and whether its bulk and surface remain representative of the intended use.
Element identity alone cannot establish the condition of a metal specimen or justify transferring results between material forms.
Composition and phase
Resolve elemental substance, alloy, compound and mixed-phase material.
Metal-bearing material identity
Record metal content, impurities and phase evidence before interpreting material properties.
- What measured composition and phase evidence distinguish elemental metal from an alloy, oxide, salt or mixture? measurement
- Which impurities or secondary phases could account for the observed response, and what are their detection limits? measurement
Surface and dispersion
Track exposed metal form and surface alteration under the relevant environment.
Surface state relevance
Establish whether surface composition and dispersion support the intended comparison or action.
- What evidence describes particle size or dispersion and any oxide, adsorbate or other surface layer? measurement
- Does the current surface condition require re-characterization before the proposed catalytic, electrochemical or material use? action
Condition-dependent responses Connect observations relevant to transition-metal chemistry with their measurement conditions and competing explanations.
Redox and electronic-response evidence is useful only when tied to a particular metal state and environment.
Redox behaviour
Assess specific metal redox couples and distinguish equilibrium evidence from observed transformation rates.
Qualified redox evidence
Record the conditions and limitations governing a proposed change in metal oxidation state.
- Which redox couple and potential were measured, against which reference electrode and in what medium? measurement
- What evidence addresses reaction rate, passivation or competing chemistry under the proposed oxidation or reduction conditions? action
Magnetic and spectroscopic response
Use measured responses to test electronic-state and coordination interpretations.
Interpretable electronic response
Preserve measurement context and competing causes of magnetic or spectral observations.
- Which magnetic or spectroscopic observations constrain the proposed metal electronic state, and under what conditions? measurement
- Could impurities, multiple species, collective solid-state effects or non-metal-centred transitions explain the response? boundary
Use and transformation decisions Translate evidence about a particular transition metal into bounded decisions about selection, transformation and handling.
A class label must not become automatic permission to assign catalytic activity, substitute materials or apply a treatment.
Role-specific suitability
Assess evidence for the precise metal form and function being proposed.
Demonstrated metal role
Link application claims to tested species, performance criteria and operating conditions.
- Which exact metal form has demonstrated the proposed catalytic, electrical, magnetic or structural role, and against what performance criterion? provenance
- What additional evidence is needed before substituting this metal or transferring the result to another oxidation state, support or material form? action
Transformation and handling constraints
Connect a proposed operation to species changes, material changes and applicable external constraints.
Bounded operation decision
Record the evidence and linked assessments required to support an operation on the identified metal-bearing material.
- Which oxidation-state, coordination, phase or surface changes are expected from the proposed operation, and how will they be checked? action
- Which hazard and process assessments apply to this exact species and form, including any powder, aerosol or dissolved-metal exposure created by the operation? boundary
Evidence and external alignment What the world already says about this thing, gathered so the model can be checked against it.
A model that cannot be lined up against existing standards, identifiers and practice cannot be adopted by anyone who already uses them.
Reported evidence
Findings from the breadth pass, kept separate from the structural claims.
Kinds and varieties
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- First-row (3d) transition metals (Sc-Cu)
- Second-row (4d) transition metals (Y-Ag)
- Third-row (5d) transition metals (Lu/Hf-Au)
- Early transition metals (groups 3-7)
- Late transition metals (groups 8-11)
- Inner transition metals (lanthanoids and actinoids), treated as a related f-block class
- Platinum-group metals (Ru, Rh, Pd, Os, Ir, Pt)
- Group 12 d-block metals (Zn, Cd, Hg, Cn), included in some teaching lists and excluded by the incomplete-d-shell test
- Which of these kinds and varieties hold for the sense of transition metal this model covers, and on what evidence? provenance
Identifiers and schemes
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Wikidata - Q19588 - Item "transition metal"; confirm on Wikidata before treating the Q-id as canonical in a registry.
- IUPAC Gold Book - transition element - Preferred IUPAC term for the class; no single CAS or UN number exists for the class as a whole.
- Periodic-table groups - groups 3-11 (IUPAC class); groups 3-12 in many general-chemistry texts - Atomic numbers typically 21-29, 39-47, 71 or 72-79, plus the 6d homologues when they are isolated.
- MeSH - D014148 - Heading "Transition Elements"; used in biomedical indexing, not as a chemical identifier for a specimen.
- Which of these identifiers and schemes hold for the sense of transition metal this model covers, and on what evidence? provenance
Standards and regulation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- IUPAC Recommendations 2005 (Red Book) and the IUPAC Gold Book - International Union of Pure and Applied Chemistry: definition and nomenclature of the class.
- IUPAC periodic table and CIAAW atomic-weight tables - International Union of Pure and Applied Chemistry / Commission on Isotopic Abundances and Atomic Weights: which elements sit in the d-block and their standard atomic weights.
- GHS / EU CLP - UNECE and the European Commission: classification, labelling and packaging apply to individual transition-metal substances and compounds, not to the class as such.
- IARC Monographs - International Agency for Research on Cancer: carcinogen evaluations for specific metals and compounds (notably Ni, Cr(VI), Cd, Co), not a class-wide listing.
- REACH and RoHS - European Union: substance restrictions and product limits for named metals (Ni, Cd, Cr(VI), Hg, and others) that overlap the class.
- Which of these standards and regulation hold for the sense of transition metal this model covers, and on what evidence? provenance
Real-world use
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Structural and tool alloys: steels and superalloys based on Fe, Ni, Co, Cr, Mo, V, Ti, W.
- Heterogeneous and homogeneous catalysis: Fe (ammonia), Ni, Pd, Pt, Rh (hydrogenation, automotive three-way catalysts, cross-coupling).
- Electrical and electronic conductors and barriers: Cu interconnects, Ag contacts, W vias, Ta/TaN and TiN barrier layers.
- Permanent magnets and soft magnetic cores: Fe, Co, Ni and their alloys; many high-energy magnets also use lanthanoids.
- Rechargeable-battery cathodes and current collectors: Ni, Co, Mn, Fe in oxide or phosphate cathodes; Cu and Ni foils.
- Pigments, platings and biomedical hardware: Cr, Co and Fe oxides as colourants; Ti and Co-Cr implants; Au, Ag, Pt in jewellery, dentistry and electrodes.
- Which of these real-world use hold for the sense of transition metal this model covers, and on what evidence? provenance
Typical measurements
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Density (298 K, elemental metal) - about 3.0 (Sc) to 22.6 (Os) - g·cm−3
- Melting point (elemental metal, groups 3-11) - about 961 (Ag) to 3422 (W); lower if group 12 is included (Hg −38.8 °C) - °C
- Electrical resistivity (293 K, elemental metal) - about 1.6 (Ag) to about 140 (Mn) - µΩ·cm
- Common oxidation states in compounds - +1 to +8 (Os, Ru reach +8; Cu, Ag often +1) - oxidation number
- d-electron count of the free atom or common cation - 1-9 for species that meet the incomplete-d-shell test; 10 for group 12 in the +2 state - electrons
- Young's modulus (elemental metal) - about 44 (Sc) to about 410 (W) - GPa
- Which of these typical measurements hold for the sense of transition metal this model covers, and on what evidence? provenance
Failure modes and hazards
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Corrosion and high-temperature oxidation; Mo, W and Re can fail catastrophically in air by volatile-oxide formation.
- Hydrogen embrittlement of ferritic steels and titanium alloys in hydrogen-bearing service.
- Toxicity and carcinogenicity of specific species: Ni metal and compounds (sensitiser; some compounds carcinogenic), Cr(VI), Cd, and some Co compounds.
- Metal-fume fever from inhalation of Zn, Cu or related fumes; chronic lung disease from hard-metal (Co-W) dust.
- Pyrophoric behaviour of fine powders and sponge (Fe, Ni, Ti, Zr and others) and runaway catalytic oxidation on high-surface-area Pt-group metals.
- Allergic contact dermatitis from Ni (and some Co and Cr) in consumer alloys.
- Which of these failure modes and hazards hold for the sense of transition metal this model covers, and on what evidence? provenance
Regional variation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- IUPAC and most inorganic texts restrict the class to groups 3-11; many US general-chemistry courses count groups 3-12 as transition metals.
- Group 3 placement is unsettled: Sc-Y-Lu versus Sc-Y-La changes whether lanthanum is a transition metal or only an inner-transition element.
- IUPAC prefers "transition element"; engineering and materials practice almost always says "transition metal".
- Older Mendeleev-style subgroup VIII (Fe, Co, Ni as a triad, with Ru-Rh-Pd and Os-Ir-Pt) is still visible in some Russian and older European tables.
- Environmental and product law uses "heavy metal" lists that overlap this class inconsistently across jurisdictions and are not an electronic-structure classification.
- Which of these regional variation hold for the sense of transition metal this model covers, and on what evidence? provenance
Neighbouring kinds and how to tell them apart
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- d-block element - The d-block is a periodic-table strip (groups 3-12). A transition metal, on the IUPAC test, must also have an incomplete d subshell in the atom or a common cation, which drops Zn, Cd and Hg in ordinary oxidation states.
- Post-transition (p-block) metal - Al, Ga, In, Sn, Pb, Bi and related metals have a filled d10 core and chemistry dominated by s/p electrons; they lack the incomplete-d-shell, highly variable oxidation-state pattern of groups 3-11.
- Inner transition metal (lanthanoid or actinoid) - f-block species with filling 4f or 5f shells. They are often taught beside transition metals but fail the d-subshell definition unless a given ion is being discussed as a d-electron system.
- Alkaline earth metal - Group 2 (s-block) metals with a closed ns2 valence shell and an almost fixed +2 state; no partly filled d shell in the common ions (except some heavy-group-2 organometallic curiosities).
- Heavy metal (toxicological / environmental use) - A density- or toxicity-based label (Pb, Hg, Cd, and varying others). It is not a periodic-table class and both includes non-transition metals and omits many light transition metals such as Ti and Sc.
- Metalloid - Si, Ge, As and neighbours show intermediate electrical conductivity and largely covalent chemistry; they are not metallic d-electron systems with typical TM coordination and redox behaviour.
- Which of these neighbouring kinds and how to tell them apart hold for the sense of transition metal this model covers, and on what evidence? provenance
Sources
- Compendium of Chemical Terminology (IUPAC Gold Book), entry "transition element" - The incomplete-d-subshell definition used for the class, and the distinction from a mere d-block listing.
- Nomenclature of Inorganic Chemistry - IUPAC Recommendations 2005 (the Red Book) - IUPAC grouping of the d-block, the preferred term transition element, and the usual exclusion of group 12 from the class.
- Advanced Inorganic Chemistry, 6th edition (Cotton, Wilkinson, Murillo, Bochmann) - Series (3d/4d/5d), early versus late chemistry, variable oxidation states, coloured ions, magnetism, and why Zn, Cd and Hg are borderline.
- Transition metal - Consensus range of the class, group-3 and group-12 disputes, and the usual neighbours (d-block, inner transition, post-transition).
What the second pass must settle
- Which authoritative definition should the registry adopt, and how should disagreements involving group 3, group 12 and inner transition terminology be represented?
- What evidentiary threshold should qualify an uncommon cationic electronic state for membership, especially when evidence is limited to unusual experimental conditions or calculations?
- Which existing Vercy element, metal, compound or material models already own parts of this concept and should be linked to avoid duplicate sources of truth?
- What minimum analytical evidence is sufficient to separate oxidation-state mixtures, coordination environments and bulk-versus-surface contributions for each intended decision?
- Which application-specific performance and handling evidence must be gathered before any proposed affordance can be treated as supported for a particular transition metal?