53IIodine126.90447 u
Iodine (I)
Iodine is a halogen with atomic number 53, in period 5 and group 17 of the periodic table. Its atomic mass is 126.90447 u and its electron configuration is [Kr] 4d¹⁰ 5s² 5p⁵. Solid at 25 °C.
Key facts
| Atomic number | 53 |
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| Atomic mass | 126.90447 u |
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| Category | Halogen |
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| Period | 5 |
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| Group | 17 |
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| Block | p |
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| Electron configuration | [Kr] 4d¹⁰ 5s² 5p⁵ |
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| Electrons per shell | 2, 8, 18, 18, 7 |
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| Electronegativity (Pauling) | 2.66 |
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| Oxidation states | −1, +1, +2, +3, +4, +5, +6, +7common in bold |
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| State at 25 °C | Solid |
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| Melting point | 386.85 K113.7 °C |
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| Boiling point | 457.4 K184.25 °C |
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| Density | 4.94 g/cm³ |
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Atomic properties
| First ionization energy | 10.451 eV |
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| Electron affinity | 295.2 kJ/mol |
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| Atomic radius | 136 pm |
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| Covalent radius | 139 pm |
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| Van der Waals radius | 198 pm |
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| Common ions | I⁻ |
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| Protons, neutrons, electrons | 53, 74, 53 |
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Physical and thermal properties
| Molar volume | 25.72 cm³/mol |
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| Heat of fusion | 7.76 kJ/mol |
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| Heat of vaporization | 20.9 kJ/mol |
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| Specific heat | 429 J/(kg·K) |
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| Thermal conductivity | 0.449 W/(m·K) |
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| Thermal expansion | 7.49 × 10⁻⁵ K⁻¹ |
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| Mohs hardness | --- |
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| Young’s modulus | --- |
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| Crystal structure | Base orthorhombic |
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| Magnetic type | Diamagnetic |
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Identification and history
| CAS number | 7553-56-2 |
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| Latin name | Iodium |
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| Discovered by | Bernard Courtois · 1811 |
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| Named by | --- |
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Natural isotopes
| Isotope | Mass (u) | Abundance |
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| 127I | 126.904473 | 100 % |
Data checked against PubChem (NIH), IUPAC, the NIST Atomic Spectra Database and the IAEA (NUBASE and AME), the same data you see in the app.
A dash (---) means there is no reliable published measurement. The app never makes one up.
See Iodine in the app
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Periodic Table