{
  "id": "electron-configuration",
  "version": "972e5eef7cd9",
  "status": "published",
  "name": "Electron Configuration Calculator",
  "question": "What is the electron configuration?",
  "summary": "Gives the ground-state electron configuration of any element from hydrogen to oganesson, in full and noble-gas form, with electrons per shell, outer-shell electrons and unpaired electrons, using NIST’s ground states.",
  "category": "chemistry",
  "url": "https://www.acalculator.org/chemistry/electron-configuration-calculator",
  "markdown": "https://www.acalculator.org/chemistry/electron-configuration-calculator.md",
  "kind": "function",
  "method": "Fill subshells in order of n + l (lower n first on a tie): 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p, with s 2, p 6, d 10 and f 14 electrons; use NIST’s ground state where it differs.",
  "assumptions": [
    "Neutral atoms in their ground state; ions are not covered.",
    "Subshells are written in shell order (3d before 4s), as NIST writes them.",
    "Elements 109 to 118 are not in NIST’s table; their configurations follow the filling order and are predictions."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "z": {
        "title": "Element",
        "description": "The element, by atomic number, symbol and name.",
        "type": "string",
        "enum": [
          "1",
          "2",
          "3",
          "4",
          "5",
          "6",
          "7",
          "8",
          "9",
          "10",
          "11",
          "12",
          "13",
          "14",
          "15",
          "16",
          "17",
          "18",
          "19",
          "20",
          "21",
          "22",
          "23",
          "24",
          "25",
          "26",
          "27",
          "28",
          "29",
          "30",
          "31",
          "32",
          "33",
          "34",
          "35",
          "36",
          "37",
          "38",
          "39",
          "40",
          "41",
          "42",
          "43",
          "44",
          "45",
          "46",
          "47",
          "48",
          "49",
          "50",
          "51",
          "52",
          "53",
          "54",
          "55",
          "56",
          "57",
          "58",
          "59",
          "60",
          "61",
          "62",
          "63",
          "64",
          "65",
          "66",
          "67",
          "68",
          "69",
          "70",
          "71",
          "72",
          "73",
          "74",
          "75",
          "76",
          "77",
          "78",
          "79",
          "80",
          "81",
          "82",
          "83",
          "84",
          "85",
          "86",
          "87",
          "88",
          "89",
          "90",
          "91",
          "92",
          "93",
          "94",
          "95",
          "96",
          "97",
          "98",
          "99",
          "100",
          "101",
          "102",
          "103",
          "104",
          "105",
          "106",
          "107",
          "108",
          "109",
          "110",
          "111",
          "112",
          "113",
          "114",
          "115",
          "116",
          "117",
          "118"
        ]
      }
    }
  },
  "outputs": {
    "full": {
      "label": "Electron configuration",
      "description": "Every occupied subshell with its electrons, in shell order.",
      "format": "text"
    },
    "noble": {
      "label": "Noble gas notation",
      "description": "The configuration after the previous noble gas’s core, written in brackets.",
      "format": "text"
    },
    "element": {
      "label": "Element",
      "description": "The element’s symbol and name.",
      "format": "text"
    },
    "shells": {
      "label": "Electrons per shell",
      "description": "The electrons in shells n = 1, 2, 3, and so on.",
      "format": "text"
    },
    "outer": {
      "label": "Outer-shell electrons",
      "description": "The electrons in the highest occupied shell (largest n).",
      "format": "integer"
    },
    "unpaired": {
      "label": "Unpaired electrons",
      "description": "Electrons alone in an orbital, by Hund’s rule, in this ground configuration.",
      "format": "integer"
    },
    "basis": {
      "label": "Source of this configuration",
      "description": "Whether the configuration is the plain filling order, a NIST exception, or a prediction beyond NIST’s table.",
      "format": "text"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "z": "26"
    },
    "outputs": {
      "full": "1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s²",
      "noble": "[Ar] 3d⁶ 4s²",
      "element": "Fe (Iron), Z = 26",
      "shells": "2, 8, 14, 2",
      "outer": 2,
      "unpaired": 4,
      "basis": "NIST ground state, the same as the filling order."
    },
    "text": "The electron configuration of Fe (Iron), Z = 26 is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s², or [Ar] 3d⁶ 4s²."
  },
  "examples": [
    {
      "given": {
        "z": "8"
      },
      "expect": {
        "full": "1s² 2s² 2p⁴",
        "noble": "[He] 2s² 2p⁴",
        "shells": "2, 6",
        "outer": 6,
        "unpaired": 2
      },
      "source": "OpenStax, Chemistry 2e, §6.4 Electronic Structure of Atoms (Electron Configurations) (aufbau order 1s 2s 2p 3s 3p 4s 3d 4p …, Hund’s rule; Cr is [Ar]3d⁵4s¹ and Cu [Ar]3d¹⁰4s¹). https://openstax.org/books/chemistry-2e/pages/6-4-electronic-structure-of-atoms-electron-configurations, retrieved 2026-10-02: oxygen is 1s²2s²2p⁴ with two unpaired electrons"
    },
    {
      "given": {
        "z": "26"
      },
      "expect": {
        "noble": "[Ar] 3d⁶ 4s²",
        "shells": "2, 8, 14, 2",
        "unpaired": 4
      },
      "source": "NIST Standard Reference Database 111, Ground Levels and Ionization Energies for the Neutral Atoms (ground configurations, Z = 1 to 108). https://www.nist.gov/pml/ground-levels-and-ionization-energies-neutral-atoms, retrieved 2026-10-02: Fe [Ar]3d⁶4s²; hand calculation in content.mdx: 3d⁶ has 4 unpaired electrons"
    },
    {
      "given": {
        "z": "24"
      },
      "expect": {
        "noble": "[Ar] 3d⁵ 4s¹",
        "unpaired": 6,
        "basis": "NIST ground state, an exception to the filling order."
      },
      "source": "NIST Standard Reference Database 111, Ground Levels and Ionization Energies for the Neutral Atoms (ground configurations, Z = 1 to 108). https://www.nist.gov/pml/ground-levels-and-ionization-energies-neutral-atoms, retrieved 2026-10-02: Cr [Ar]3d⁵4s¹; OpenStax, Chemistry 2e, §6.4 Electronic Structure of Atoms (Electron Configurations) (aufbau order 1s 2s 2p 3s 3p 4s 3d 4p …, Hund’s rule; Cr is [Ar]3d⁵4s¹ and Cu [Ar]3d¹⁰4s¹). https://openstax.org/books/chemistry-2e/pages/6-4-electronic-structure-of-atoms-electron-configurations, retrieved 2026-10-02"
    },
    {
      "given": {
        "z": "29"
      },
      "expect": {
        "full": "1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s¹",
        "noble": "[Ar] 3d¹⁰ 4s¹",
        "unpaired": 1
      },
      "source": "NIST Standard Reference Database 111, Ground Levels and Ionization Energies for the Neutral Atoms (ground configurations, Z = 1 to 108). https://www.nist.gov/pml/ground-levels-and-ionization-energies-neutral-atoms, retrieved 2026-10-02: Cu [Ar]3d¹⁰4s¹; OpenStax, Chemistry 2e, §6.4 Electronic Structure of Atoms (Electron Configurations) (aufbau order 1s 2s 2p 3s 3p 4s 3d 4p …, Hund’s rule; Cr is [Ar]3d⁵4s¹ and Cu [Ar]3d¹⁰4s¹). https://openstax.org/books/chemistry-2e/pages/6-4-electronic-structure-of-atoms-electron-configurations, retrieved 2026-10-02"
    },
    {
      "given": {
        "z": "103"
      },
      "expect": {
        "noble": "[Rn] 5f¹⁴ 7s² 7p¹",
        "outer": 3
      },
      "source": "NIST Standard Reference Database 111, Ground Levels and Ionization Energies for the Neutral Atoms (ground configurations, Z = 1 to 108). https://www.nist.gov/pml/ground-levels-and-ionization-energies-neutral-atoms, retrieved 2026-10-02: Lr [Rn]5f¹⁴7s²7p¹"
    },
    {
      "given": {
        "z": "118"
      },
      "expect": {
        "noble": "[Rn] 5f¹⁴ 6d¹⁰ 7s² 7p⁶",
        "shells": "2, 8, 18, 32, 32, 18, 8",
        "unpaired": 0
      },
      "source": "hand calculation in content.mdx: the Madelung order fills 7p last; OpenStax, Chemistry 2e, §6.4 Electronic Structure of Atoms (Electron Configurations) (aufbau order 1s 2s 2p 3s 3p 4s 3d 4p …, Hund’s rule; Cr is [Ar]3d⁵4s¹ and Cu [Ar]3d¹⁰4s¹). https://openstax.org/books/chemistry-2e/pages/6-4-electronic-structure-of-atoms-electron-configurations, retrieved 2026-10-02"
    }
  ],
  "sources": [
    "OpenStax, Chemistry 2e, §6.4 Electronic Structure of Atoms (Electron Configurations): the aufbau order, s 2, p 6, d 10 and f 14 electrons, Hund’s rule, oxygen 1s²2s²2p⁴ with two unpaired electrons, and the chromium ([Ar]3d⁵4s¹) and copper ([Ar]3d¹⁰4s¹) exceptions. https://openstax.org/books/chemistry-2e/pages/6-4-electronic-structure-of-atoms-electron-configurations (retrieved 2026-10-02)",
    "NIST Standard Reference Database 111, Ground Levels and Ionization Energies for the Neutral Atoms (ground-state configurations for Z = 1 to 108, in its HTML table in the NIST Atomic Spectra Database). https://www.nist.gov/pml/ground-levels-and-ionization-energies-neutral-atoms (retrieved 2026-10-02)",
    "CIAAW (IUPAC Commission on Isotopic Abundances and Atomic Weights), Standard atomic weights: element names and symbols for Z = 1 to 118. https://www.ciaaw.org/atomic-weights.htm (retrieved 2026-10-02)"
  ],
  "related": [
    "molar-mass",
    "chemical-equation-balancer",
    "half-life"
  ],
  "changelog": []
}