Element: Iodine
General data
| Element name | Iodine |
|---|---|
| Chemical symbol | I |
| Atomic number Z | 53 |
| Year discovered | 1811 |
| Standard state (25°C) | Solid |
| Category | Halogen |
| Block | p |
| Atomic mass | 126.90 |
| CPK color | #940094 |
Physical properties
| Melting point | 386.85 K (113.70 °C) |
|---|---|
| Boiling point | 457.55 K (184.40 °C) |
| Density | 4.93 g/cm³ |
Energy properties
| First ionization energy | 10.451 eV |
|---|---|
| Electron affinity | 3.059 eV |
Atomic structure
| Protons | 53 (Atomic number) |
|---|---|
| Neutrons (I-127, most abundant isotope) | 74 |
| Electrons | 53 |
| Electron configuration | [Kr] 5s² 4d¹⁰ 5p⁵ |
| Oxidation states | +7, +5, +1, -1 |
| Electronegativity (Pauling) | 2.66 |
| Atomic radius (van der Waals) | 198 pm |
Ionization energies - NIST ASD (53 states)
| State | Charge | Ioniz. energy (eV) | Type |
|---|---|---|---|
| I I | 0+ | 10.451236 ± 0.000025 | measured |
| I II | 1+ | 19.13126 ± 0.00012 | measured |
| I III | 2+ | 29.57 ± 0.025 | measured |
| I IV | 3+ | 40.357 ± 0.025 | measured |
| I V | 4+ | 51.52 ± 0.04 | measured |
| I VI | 5+ | 74.4 ± 0.4 | semi-empirical |
| I VII | 6+ | 87.61 ± 0.06 | semi-empirical |
| I VIII | 7+ | 150.81 ± 0.1 | measured |
| I IX | 8+ | 171 ± 2.2 | calculated |
| I X | 9+ | 197 ± 2.2 | calculated |
| I XI | 10+ | 220.9 ± 2.4 | calculated |
| I XII | 11+ | 247 ± 2.5 | calculated |
| I XIII | 12+ | 279 ± 3 | calculated |
| I XIV | 13+ | 307 ± 3 | calculated |
| I XV | 14+ | 335 ± 3 | calculated |
| I XVI | 15+ | 365 ± 3 | calculated |
| I XVII | 16+ | 393 ± 3 | calculated |
| I XVIII | 17+ | 505 ± 3 | calculated |
| I XIX | 18+ | 535 ± 3 | calculated |
| I XX | 19+ | 569 ± 4 | calculated |
| I XXI | 20+ | 601 ± 4 | calculated |
| I XXII | 21+ | 649 ± 4 | calculated |
| I XXIII | 22+ | 683 ± 4 | calculated |
| I XXIV | 23+ | 762 ± 4 | calculated |
| I XXV | 24+ | 800.8 ± 0.4 | semi-empirical |
| I XXVI | 25+ | 1397 ± 4 | calculated |
| I XXVII | 26+ | 1472 ± 4 | calculated |
| I XXVIII | 27+ | 1553 ± 4 | calculated |
| I XXIX | 28+ | 1639 ± 4 | calculated |
| I XXX | 29+ | 1720 ± 4 | calculated |
| I XXXI | 30+ | 1812 ± 4 | calculated |
| I XXXII | 31+ | 1911 ± 4 | calculated |
| I XXXIII | 32+ | 1999 ± 4 | calculated |
| I XXXIV | 33+ | 2093 ± 5 | calculated |
| I XXXV | 34+ | 2181 ± 5 | calculated |
| I XXXVI | 35+ | 2431 ± 5 | calculated |
| I XXXVII | 36+ | 2510 ± 5 | calculated |
| I XXXVIII | 37+ | 2598 ± 4 | calculated |
| I XXXIX | 38+ | 2680 ± 4 | calculated |
| I XL | 39+ | 2836 ± 4 | calculated |
| I XLI | 40+ | 2926 ± 4 | calculated |
| I XLII | 41+ | 3096 ± 4 | calculated |
| I XLIII | 42+ | 3185.5 ± 0.5 | semi-empirical |
| I XLIV | 43+ | 7337 ± 4 | calculated |
| I XLV | 44+ | 7563 ± 4 | calculated |
| I XLVI | 45+ | 7811 ± 4 | calculated |
| I XLVII | 46+ | 8044 ± 4 | calculated |
| I XLVIII | 47+ | 8601 ± 4 | calculated |
| I XLIX | 48+ | 8867 ± 4 | calculated |
| I L | 49+ | 9196 ± 4 | calculated |
| I LI | 50+ | 9421.1 ± 0.04 | calculated |
| I LII | 51+ | 38717 ± 0.03 | calculated |
| I LIII | 52+ | 39721.549 ± 0.017 | calculated |
Value type as given by NIST ASD: measured - from evaluated experimental data; calculated - from ab initio calculations (mostly highly ionised atoms that have not been measured; for the simplest ones, e.g. H I, the calculation is more accurate than measurement); semi-empirical - from interpolation, extrapolation or another semi-empirical method.
Photos
Isotopes (40)
| A | N | Half-life | Decay |
|---|---|---|---|
| I-108 | 55 | 26.4 ms | α |
| I-109 | 56 | 92.7 μs | p |
| I-110 | 57 | 0.67 s | α |
| I-111 | 58 | 2.5 s | EC/β⁺ |
| I-112 | 59 | 3.34 s | EC/β⁺ |
| I-113 | 60 | 5.9 s | EC/β⁺ |
| I-114 | 61 | 2.1 s | EC/β⁺ |
| I-115 | 62 | 1.3 min | EC/β⁺ |
| I-116 | 63 | 2.91 s | EC/β⁺ |
| I-117 | 64 | 2.22 min | EC/β⁺ |
| I-118 | 65 | 13.8 min | EC/β⁺ |
| I-119 | 66 | 18.8 min | EC/β⁺ |
| I-120 | 67 | 81.7 min | EC/β⁺ |
| I-121 | 68 | 2.12 h | EC/β⁺ |
| I-122 | 69 | 3.63 min | EC/β⁺ |
| I-123 | 70 | 13.2229 h | EC/β⁺ |
| I-124 | 71 | 4.1760 d | EC/β⁺ |
| I-125 | 72 | 59.398 d | EC |
| I-126 | 73 | 12.93 d | β⁻ |
| I-127 | 74 | stable | - |
| I-128 | 75 | 25.00 min | β⁻ |
| I-129 | 76 | 1.613×10⁷ a | β⁻ |
| I-130 | 77 | 12.36 h | β⁻ |
| I-131 | 78 | 8.0247 d | β⁻ |
| I-132 | 79 | 2.2839 h | β⁻ |
| I-133 | 80 | 20.8 h | β⁻ |
| I-134 | 81 | 52.6 min | β⁻ |
| I-135 | 82 | 6.55 h | β⁻ |
| I-136 | 83 | 83.4 s | β⁻ |
| I-137 | 84 | 24.13 s | β⁻ |
| I-138 | 85 | 6.30 s | β⁻ |
| I-139 | 86 | 2.29 s | β⁻ |
| I-140 | 87 | 380 ms | β⁻ |
| I-141 | 88 | 418 ms | β⁻ |
| I-142 | 89 | 235 ms | β⁻ |
| I-143 | 90 | 182 ms | β⁻ |
| I-144 | 91 | 94 ms | β⁻ |
| I-145 | 92 | 90 ms | β⁻ |
| I-146 | 93 | 90 ms | β⁻ |
| I-147 | 94 | unknown | β⁻ |
Data sources
- PubChem Periodic Table API - Retrieved on 29 June 2026 - licence: CC0
- IUPAC CIAAW - Abridged Standard Atomic Weights 2024 - Table version: 2024 - licence: Public domain
- NNDC Wallet Cards 2023 - Data as of 15 October 2024 - licence: Public domain
- NIST Atomic Spectra Database (ASD) - Retrieved on 29 June 2026 - licence: © U.S. Secretary of Commerce
- Images of Elements - Retrieved on 29 June 2026 - licence: CC BY 3.0