Iodine (I) – element 53
Iodine is a chemical element with the symbol I and atomic number 53. It is a reactive nonmetal in group 17 (halogens), period 5 of the periodic table (p-block), and is a solid at room temperature.
Iodine (I) has atomic number 53, atomic mass 126.9 u and electron configuration [Kr] 4d10 5s2 5p5.
Iodine facts
| Symbol | I |
|---|---|
| Atomic number | 53 |
| Atomic mass | 126.9 u (g/mol) |
| Category | reactive nonmetal |
| Group | group 17 (halogens) |
| Period | 5 |
| Block | p-block |
| Phase at 20 °C | Solid |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p5 |
| Noble-gas notation | [Kr] 4d10 5s2 5p5 |
| Electrons per shell | 2, 8, 18, 18, 7 |
| Valence electrons | 7 |
Bohr model and shells
Iodine has 53 electrons in 5 shells: 2, 8, 18, 18, 7. Full configuration and noble-gas notation are in the table; work out any element or ion with the electron configuration calculator.
Physical and atomic properties
| Melting point | 386.85 K (113.7 °C) |
|---|---|
| Boiling point | 457.4 K (184.2 °C) |
| Density | 4.933 g/cm³ |
| Electronegativity (Pauling) | 2.66 |
| Electron affinity | 295.153 kJ/mol |
| Ionization energies | 1008.4, 1845.9, 3180 kJ/mol (1st, 2nd, 3rd) |
| Discovered by | Bernard Courtois |
Use the atomic mass in the molar mass calculator for any formula containing I.
Position in the periodic table
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Frequently asked questions
What is the atomic mass of iodine?
The atomic mass of iodine is 126.9 u, so one mole of iodine atoms weighs 126.9 g.
What is the electron configuration of iodine?
Iodine has 53 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁵, or [Kr] 4d¹⁰ 5s² 5p⁵ in noble-gas notation. Electrons per shell: 2, 8, 18, 18, 7.
How many valence electrons does iodine have?
Iodine has 7 valence electrons (group 17).
Is iodine a metal?
No. Iodine is a nonmetal (reactive nonmetal).
Where is iodine on the periodic table?
Iodine is in group 17 (halogens), period 5, in the p-block.
Data: Periodic-Table-JSON (CC BY-SA 3.0); standard atomic weights from IUPAC (abridged). Values in brackets are the mass number of the longest-lived isotope.