alkaline earth metal
Enable an AI agent to recognise an alkaline earth metal, assess the condition of a particular material and determine which handling, transformation or use decisions its recorded evidence supports.
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 recognise an alkaline earth metal, assess the condition of a particular material and determine which handling, transformation or use decisions its recorded evidence supports.
An alkaline earth metal is any of the six IUPAC Group 2 s-block elements (Be, Mg, Ca, Sr, Ba, Ra) with a closed ns² valence configuration, which form predominantly M²⁺ cations and basic oxides historically called alkaline earths, with metallic and ionic character increasing down the group.
It can be Identify a specimen as a particular Group 2 metal or flag insufficient or conflicting evidence.; Assess whether alteration or mixing requires representation as a composite, alloy or compound.; Compare measured behaviour with references matched to element, form and conditions.; Evaluate proposed storage media and contact materials against documented compatibility evidence.; Determine whether cutting, grinding, heating or chemical transformation is supported by the recorded material state and applicable controls.; Select additional characterisation needed before accepting a material for an intended use..
Distinguishing features
Elemental identity must resolve to Be, Mg, Ca, Sr, Ba or Ra; metallic appearance or alkaline reaction products alone do not establish membership.
Group 2 membership distinguishes these elements from Group 1 alkali metals; similar names or water reactivity are insufficient identification tests.
Evidence must distinguish elemental metal from an oxide, hydroxide, salt or dissolved ion containing the same element; detecting calcium, for example, does not establish calcium metal.
A material containing an alkaline earth element must be assessed for alloy or mixture status before the whole material is classified as that elemental metal.
Weak or absent reaction in a particular test does not alone exclude Group 2 identity; element, surface condition and test conditions must be recorded.
Scope
+ Identification of the Group 2 element and evidence supporting that identification
+ Elemental-metal content, impurities and boundaries between metal, alloy and compound
+ Physical form, phase and surface alteration of a material specimen
+ Element-specific chemical behaviour under recorded environmental conditions
+ Material properties and hazards that constrain handling, storage, processing and use
- Detailed identities and behaviour of alkaline earth compounds, minerals and dissolved ions
- Alloy design and properties of mixtures that require their own material models
- Mining, refining and manufacturing workflows as complete processes
- Biological roles, exposure assessment and clinical management
- Radioactive decay chains, radiation facilities and waste-management systems
Characteristics
- Elemental identity
- beryllium | magnesium | calcium | strontium | barium | radium | unresolved Establishes membership and prevents family-level expectations from substituting for element-specific evidence.
- Identity evidence
- Links to analytical results, material certificates or other identification records Makes recognition traceable and exposes conflicts between labels and measurements.
- Elemental-metal mass fraction
- Mass fraction or mass %, with method, uncertainty and sampling basis Distinguishes metal content from total elemental content, including that present in compounds.
- Impurity and alloying composition
- Constituent mass fractions, with detection limits Supports the boundary between an elemental-metal specimen and an alloy and helps explain altered behaviour.
- Physical form
- bulk piece | sheet | ribbon | turnings | powder | other recorded form Surface exposure and dispersibility affect reaction, processing and exposure decisions.
- Particle size or exposed surface
- Particle-size distribution in µm or mm; exposed area in m² or specific surface area in m²/kg Allows observations on finely divided material to be distinguished from observations on bulk metal.
- Surface condition
- Freshly exposed | characterised surface film | visibly altered | contaminated | unknown, with evidence Surface layers can change observed behaviour without changing the identity of the underlying metal.
- Temperature and phase
- Temperature in K or °C; solid | liquid | vapour | mixed | unresolved Properties and permitted operations depend on the material's current physical state.
- Contact environment
- Links to contacting gases, liquids, solids or protective media, with humidity, temperature and duration where relevant Connects deterioration and compatibility judgements to actual exposure conditions.
- Isotopic and radiological characterisation
- Isotope fractions and activity in Bq or Bq/g where relevant; unknown explicitly recorded Supports isotope-dependent restrictions, particularly for radium, that chemical identity alone cannot resolve.
Where this came from
wikidata · CC0 1.0
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 5 bundles · 9 layers · 16 findings · 29 questions.
Group 2 identity and material boundary Establishes which alkaline earth element is represented and whether the material is actually in elemental-metal form.
An element name, a positive elemental analysis and a metallic specimen are different assertions that must not be conflated.
Element membership
Resolves identity within the six Group 2 elements.
Supported element assignment
Records the proposed elemental identity and the evidence needed to accept it.
- Which of Be, Mg, Ca, Sr, Ba or Ra is represented, and does the record describe an element type or a particular specimen? definition
- Which analytical result or traceable material record supports that identity, and are there contradictory observations? provenance
Metal, compound and alloy boundary
Separates elemental metal from materials that merely contain the element.
Elemental-metal status
Establishes whether the specimen is predominantly metal, a metal with alteration products or a material requiring a neighbouring model.
- What evidence distinguishes elemental metal from oxides, hydroxides, salts or other compounds containing the same element? measurement
- Do alloying constituents or compound phases require a linked alloy, mixture or compound model? boundary
Metal form and condition Captures the bulk and surface states that determine how a specimen behaves.
A bulk piece, powder and surface-altered specimen of the same element can support different handling and performance decisions.
Bulk form and phase
Records geometry, particle scale and thermal state.
Condition-specific physical properties
Connects the specimen's form and measured properties to the conditions under which they apply.
- What are the material's physical form, dimensions or particle-size distribution, temperature and phase? measurement
- Which density, conductivity or mechanical-property evidence applies to this element, purity, form and temperature? provenance
Surface film and alteration
Distinguishes the metallic interior from surface products and contamination.
Surface-controlled condition
Records surface alteration and whether it explains changes in observed behaviour.
- What surface film or contamination has been identified, and what is known about its extent or thickness? measurement
- What evidence establishes whether the surface layer limits further reaction under the recorded conditions? provenance
- At what observed extent of alteration should the specimen be represented as metal plus reaction products rather than as an unqualified metal? boundary
Element-specific reactivity Organises evidence about chemical behaviour without treating all alkaline earth metals as interchangeable.
Group membership alone cannot establish reaction rate, compatibility or the effect of a surface film.
Air and water response
Records behaviour during contact with oxygen, humidity, liquid water or steam.
Environment-conditioned reaction
Connects reaction observations to the specific element, form, surface and exposure conditions.
- What reaction, temperature change, gas evolution or material loss was observed during a documented air, moisture, water or steam exposure? measurement
- Which element, particle scale, surface condition, temperature and exposure duration does that observation cover? boundary
- What additional evidence is needed before using the observation to judge a proposed exposure? action
Chemical contact and conversion
Assesses proposed contacts and transformations using evidence specific to the metal.
Supported chemical compatibility
Records compatibility and transformation evidence for identified contacting substances.
- Which documented evidence covers contact with the proposed acid, base, solvent, gas or solid at the intended concentration and temperature? provenance
- Which reaction products, heat release or gas generation must be accounted for before permitting the proposed contact? action
- When conversion occurs, which resulting compounds or mixtures need their own linked models? boundary
Handling and use eligibility Relates the metal's identity and current condition to storage, processing and application decisions.
The family includes materially different chemical, exposure and radiological concerns, so permission to act must depend on the identified element and specimen.
Element and form-specific controls
Links hazards and controls to the actual metal, including dust-generating operations and relevant isotopes.
Supported handling envelope
Records the conditions under which proposed handling or storage is supported by applicable evidence.
- Which current material-specific sources establish the controls for this element and form, including beryllium exposure or radium radiological controls where applicable? provenance
- Are the proposed atmosphere, protective medium and container materials supported for this metal's condition and intended storage duration? action
- Would cutting, grinding or heating change the form or exposure conditions enough to require reassessment? action
Fitness for intended operation
Tests whether the recorded specimen can support a stated processing step or material function.
Use-specific acceptance
Connects intended performance to verified composition, surface condition and physical properties.
- Which limits on metal content, impurities, surface alteration and physical form does the intended operation require? boundary
- Which measurements demonstrate that this specimen meets those limits? measurement
- Can the proposed operation proceed on the available evidence, or which unresolved condition requires further characterisation? action
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.
- beryllium (Be): small, highly polarizing cation and largely covalent chemistry
- magnesium (Mg)
- calcium (Ca)
- strontium (Sr)
- barium (Ba)
- radium (Ra): radioactive member of the group
- light alkaline-earth metals (Be, Mg), as distinguished in materials and organometallic chemistry
- heavy alkaline-earth metals (Ca, Sr, Ba, Ra), as distinguished in inorganic and geochemical practice
- Which of these kinds and varieties hold for the sense of alkaline earth 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 - Q19564 - Item for the alkaline earth metal group, not a single element.
- IUPAC periodic-table group - 2 - Current group number; members Be, Mg, Ca, Sr, Ba, Ra.
- CAS group notation (obsolete) - IIA - Still seen in older US textbooks; same six elements.
- IUPAC element symbols - Be | Mg | Ca | Sr | Ba | Ra
- atomic number - 4 | 12 | 20 | 38 | 56 | 88
- CAS Registry Number - 7440-41-7 (Be); 7439-95-4 (Mg); 7440-70-2 (Ca); 7440-24-6 (Sr); 7440-39-3 (Ba); 7440-14-4 (Ra) - Elemental metals, not compounds.
- Which of these identifiers and schemes hold for the sense of alkaline earth 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 Nomenclature of Inorganic Chemistry (Red Book, 2005) and the IUPAC Periodic Table of the Elements - Group 2 membership and naming (IUPAC).
- OSHA 29 CFR 1910.1024 - occupational exposure to beryllium (United States Department of Labor).
- IARC Monographs on beryllium and beryllium compounds - classified as carcinogenic to humans, Group 1 (International Agency for Research on Cancer).
- IAEA International Basic Safety Standards and national radiation-protection law - control of 226Ra, 228Ra and 90Sr as bone-seeking radionuclides.
- Pharmacopoeial monographs for barium sulfate (USP, Ph. Eur.) - insoluble BaSO4 as a medical contrast medium, distinct from soluble barium salts.
- ASTM and ISO product standards for magnesium and magnesium alloys (e.g. ASTM B93; ISO 16220) - composition and form of commercial Mg metal products.
- Which of these standards and regulation hold for the sense of alkaline earth 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.
- Magnesium structural alloys in automotive and aerospace die-castings, and organomagnesium (Grignard) reagents in organic synthesis.
- Calcium oxide, hydroxide and carbonate in Portland cement, steelmaking flux, soil amendment and food/pharmaceutical calcium salts.
- Dissolved Ca2+ and Mg2+ as the principal contributors to natural-water hardness and to scale in boilers and domestic plumbing.
- Barium sulfate as a high-density weighting agent in oil-well drilling muds and as an oral/rectal radiographic contrast medium.
- Strontium nitrate and carbonate in red pyrotechnic compositions, and strontium ferrite in ceramic permanent magnets; 89Sr used in palliative bone therapy.
- Beryllium metal X-ray windows and Be-Cu alloys in aerospace, electronics and non-sparking tools.
- Radium-226 as a historical constituent of luminous paints and, today, as a regulated NORM/TENORM and nuclear-legacy contaminant rather than a commodity metal.
- Which of these real-world use hold for the sense of alkaline earth 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.
- atomic number (Z) - 4-88 - 1
- first ionization energy - about 500-900 - kJ/mol
- standard reduction potential E°(M2+/M) - about −1.97 (Be) to −2.92 (Ra) - V vs SHE
- Shannon ionic radius of M2+ (coordination number 6) - about 45 (Be2+) to 148 (Ra2+) - pm
- density of the elemental metal (room temperature) - about 1.5-5.5 - g/cm3
- melting point of the elemental metal - about 650 (Mg) to 1287 (Be) - °C
- crustal abundance - Ca and Mg at percent level; Sr and Ba hundreds of mg/kg; Be a few mg/kg; Ra at trace (decay-series) level - mg/kg
- Which of these typical measurements hold for the sense of alkaline earth 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.
- Soluble barium salts are highly toxic (hypokalemia, muscle paralysis, cardiac arrhythmia); insoluble BaSO4 used medically must not be confused with them.
- Beryllium metal and compounds cause chronic beryllium disease (sensitization and granulomatous lung disease) and are IARC Group 1 carcinogens; Be dust and fumes are the usual exposure path.
- Radium is an alpha-emitting, bone-seeking radionuclide (historical 'radium jaw' and osteosarcoma); 90Sr is the analogous hazard among strontium isotopes.
- Ca, Sr and Ba metals react with water to give hydrogen and heat; the reaction becomes vigorous to violent down the group and can cause fire or explosion in confined wet storage.
- Magnesium metal fires burn at high temperature and are not extinguished by water or carbon dioxide; they require Class D dry-powder methods.
- Beryllium oxide is amphoteric and the metal is passivated, so Be does not show the water reactivity of the heavier members; treating it as a typical Group 2 metal underestimates its inhalation toxicity and overestimates its aqueous reactivity.
- Which of these failure modes and hazards hold for the sense of alkaline earth 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.
- Older US teaching still labels the group CAS IIA; IUPAC and most current international use is Group 2.
- In mineralogy and older European literature, 'alkaline earth' often named the oxide (CaO, BaO, etc.) rather than the metal.
- Some older Central European and textbook traditions treated beryllium as not a 'typical' alkaline earth because BeO is amphoteric and Be chemistry is largely covalent.
- Water-hardness practice differs: US reports are often grains per gallon as CaCO3 equivalent; WHO/EU practice is mg/L as CaCO3 or as Ca and Mg separately.
- National names (German Erdalkalimetalle, French métaux alcalino-terreux, Russian щелочноземельные металлы) refer to the same IUPAC group; local product standards for Mg alloys and Be occupational limits differ by jurisdiction.
- Which of these regional variation hold for the sense of alkaline earth 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.
- alkali metal (IUPAC Group 1) - ns1 configuration and stable M+ rather than ns2 and M2+; alkali hydroxides are more soluble and stronger bases, and flame tests plus ionic charge/mass (or a simple solubility pattern of carbonates and sulfates) separate the two groups.
- rare-earth metal (Sc, Y and the lanthanoids) - Typically M3+ chemistry with characteristic 4f spectra and magnetism; not s-block Group 2, despite the shared historical word 'earth'.
- aluminium and other classical 'earth' metals - Al3+ with an amphoteric oxide; not Group 2. Distinguish by oxidation state, amphoteric vs basic oxide, and the absence of the Group 2 ns2 metallic lattice.
- helium - Also 1s2, but a noble gas, not a metal; no condensed metallic phase under ordinary conditions and no M2+ aqueous chemistry.
- alkaline-earth metal oxide ('alkaline earth') - The historical earth is the oxide (e.g. lime, baryta), not the element; the metal is obtained by reduction or electrolysis of the salt or oxide.
- Which of these neighbouring kinds and how to tell them apart hold for the sense of alkaline earth metal this model covers, and on what evidence? provenance
Sources
- Chemistry of the Elements, 2nd ed. (N. N. Greenwood and A. Earnshaw; Butterworth-Heinemann) - Group 2 electronic structure, periodic trends, reactivity with water and air, and the historical meaning of alkaline earths as the oxides.
- Nomenclature of Inorganic Chemistry, IUPAC Recommendations 2005 (Red Book) (IUPAC; Royal Society of Chemistry) - Official IUPAC Group 2 numbering and the membership of the group as Be, Mg, Ca, Sr, Ba and Ra.
- CRC Handbook of Chemistry and Physics (CRC Press / Taylor & Francis) - Typical ranges for ionization energy, density, melting point, ionic radius and standard potentials of the Group 2 metals.
- Alkaline earth metal (Wikimedia Foundation) - Conventional membership of the group, common uses, and the distinction from alkali metals and rare-earth metals.
What the second pass must settle
- Does the registry intend this entry to own the Group 2 family only, individual metal specimens, or both through linked element-specific models?
- Which authoritative references and analytical methods should establish elemental-metal content separately from total elemental content?
- Which element-specific evidence is needed to characterise surface films and their effects across bulk, finely divided and heated material?
- What documented criteria should govern transitions from an elemental-metal specimen to an alloy, mixture or substantially converted material?
- Which current sources should govern handling and use decisions for each element and form, particularly beryllium-containing dust and radium specimens?