{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$id": "element-data.schema.json",
  "title": "Chemical Element Data",
  "description": "Array of chemical element data for all 118 elements",
  "type": "array",
  "minItems": 118,
  "maxItems": 118,
  "items": {
    "type": "object",
    "required": [
      "number",
      "symbol",
      "name",
      "atomic_mass",
      "row",
      "column",
      "period",
      "category"
    ],
    "properties": {
      "number": {
        "type": "integer",
        "minimum": 1,
        "maximum": 118,
        "description": "Atomic number (Z)"
      },
      "symbol": {
        "type": "string",
        "pattern": "^[A-Z][a-z]?$",
        "description": "Element symbol (1-2 characters)"
      },
      "name": {
        "type": "string",
        "description": "Full element name"
      },
      "atomic_mass": {
        "type": "number",
        "minimum": 0,
        "description": "Atomic mass in atomic mass units (u)"
      },
      "row": {
        "type": "integer",
        "minimum": 1,
        "maximum": 10,
        "description": "Periodic table row (1-7 for main, 8-9 for lanthanides, 9-10 for actinides in some layouts)"
      },
      "column": {
        "type": "integer",
        "minimum": 1,
        "maximum": 18,
        "description": "Periodic table column (group, 1-18)"
      },
      "period": {
        "type": "integer",
        "minimum": 1,
        "maximum": 7,
        "description": "Periodic table period"
      },
      "category": {
        "type": "string",
        "enum": [
          "actinide",
          "alkali metal",
          "alkaline earth metal",
          "diatomic nonmetal",
          "lanthanide",
          "metalloid",
          "noble gas",
          "polyatomic nonmetal",
          "post-transition metal",
          "transition metal"
        ],
        "description": "Element category"
      },
      "appearance": {
        "type": ["string", "null"],
        "description": "Physical appearance"
      },
      "density": {
        "type": "number",
        "description": "Density in g/cm³"
      },
      "discoverer": {
        "type": "string",
        "description": "Discoverer name(s)"
      },
      "molar_heat": {
        "type": ["number", "null"],
        "description": "Molar heat capacity in J/(mol·K)"
      },
      "phase": {
        "type": "string",
        "enum": ["Gas", "Liquid", "Solid"],
        "description": "Standard state phase"
      },
      "spectral_img": {
        "type": ["string", "null"],
        "description": "URL to spectral image"
      },
      "summary": {
        "type": "string",
        "description": "Brief description of the element"
      },
      "shells": {
        "type": "array",
        "items": { "type": "integer", "minimum": 0 },
        "description": "Electron shell configuration"
      },
      "electron_configuration": {
        "type": "string",
        "description": "Full electron configuration"
      },
      "electron_configuration_semantic": {
        "type": "string",
        "description": "Semantic electron configuration with noble gas core"
      },
      "electron_affinity": {
        "type": ["number", "null"],
        "description": "Electron affinity in kJ/mol"
      },
      "electronegativity_pauling": {
        "type": ["number", "null"],
        "description": "Pauling electronegativity"
      },
      "electronegativity": {
        "type": ["number", "null"],
        "description": "Electronegativity (same as Pauling)"
      },
      "ionization_energies": {
        "type": "array",
        "items": { "type": "number" },
        "description": "Ionization energies in kJ/mol"
      },
      "cpk-hex": {
        "type": ["string", "null"],
        "pattern": "^[0-9a-fA-F]{6}$",
        "description": "CPK color as hex string (without #)"
      },
      "neutrons": {
        "type": "integer",
        "minimum": 0,
        "description": "Number of neutrons in most common isotope"
      },
      "protons": {
        "type": "integer",
        "minimum": 1,
        "description": "Number of protons (same as atomic number)"
      },
      "electrons": {
        "type": "integer",
        "minimum": 1,
        "description": "Number of electrons in neutral atom"
      },
      "radioactive": {
        "type": ["boolean", "null"],
        "description": "Whether element is radioactive"
      },
      "natural": {
        "type": ["boolean", "null"],
        "description": "Whether element occurs naturally"
      },
      "metal": {
        "type": ["boolean", "null"],
        "description": "Whether element is a metal"
      },
      "nonmetal": {
        "type": ["boolean", "null"],
        "description": "Whether element is a nonmetal"
      },
      "metalloid": {
        "type": ["boolean", "null"],
        "description": "Whether element is a metalloid"
      },
      "atomic_radius": {
        "type": ["number", "null"],
        "description": "Atomic radius in Angstroms"
      },
      "covalent_radius": {
        "type": ["number", "null"],
        "description": "Covalent radius in Angstroms"
      },
      "first_ionization": {
        "type": ["number", "null"],
        "description": "First ionization energy in eV"
      },
      "melting_point": {
        "type": ["number", "null"],
        "description": "Melting point in Kelvin"
      },
      "boiling_point": {
        "type": ["number", "null"],
        "description": "Boiling point in Kelvin"
      },
      "number_of_isotopes": {
        "type": ["integer", "null"],
        "description": "Number of known isotopes"
      },
      "year": {
        "type": ["integer", "string"],
        "description": "Year of discovery"
      },
      "specific_heat": {
        "type": ["number", "null"],
        "description": "Specific heat capacity in J/(g·K)"
      },
      "n_shells": {
        "type": "integer",
        "minimum": 1,
        "description": "Number of electron shells"
      },
      "n_valence": {
        "type": ["integer", "null"],
        "description": "Number of valence electrons"
      },
      "oxidation_states": {
        "type": "array",
        "items": { "type": "integer" },
        "description": "All known oxidation states"
      },
      "common_oxidation_states": {
        "type": "array",
        "items": { "type": "integer" },
        "description": "Common oxidation states"
      },
      "icsd_oxidation_states": {
        "type": "array",
        "items": { "type": "integer" },
        "description": "ICSD oxidation states (oxidation states with at least 10 instances in ICSD)"
      },
      "ionic_radii": {
        "type": ["object", "null"],
        "additionalProperties": { "type": "number" },
        "description": "Ionic radii by oxidation state (string keys like '2', '-1')"
      },
      "shannon_radii": {
        "type": ["object", "null"],
        "description": "Shannon radii: oxidation_state -> coordination -> spin -> {crystal_radius, ionic_radius}",
        "additionalProperties": {
          "type": "object",
          "additionalProperties": {
            "type": "object",
            "additionalProperties": {
              "type": "object",
              "properties": {
                "crystal_radius": { "type": "number" },
                "ionic_radius": { "type": "number" }
              },
              "required": ["crystal_radius", "ionic_radius"]
            }
          }
        }
      }
    }
  }
}