Iodine (I)
Iodine is element 53, a halogen in period 5, group 17 of the periodic table. At room temperature it is a solid.
Electron configuration [Kr] 4d10 5s2 5p5
Electrons per shell 2, 8, 18, 18, 7
Iodine data
| Atomic number | 53 |
|---|---|
| Symbol | I |
| Atomic mass | 126.904 u |
| Category | Halogen |
| Group | 17 |
| Period | 5 |
| Block | p |
| State at 25 °C | solid |
| Melting point | 387 K (113.9 °C) |
| Boiling point | 457 K (183.9 °C) |
| Density | 4.94 g/cm³ |
| Electronegativity (Pauling) | 2.66 |
| Atomic radius | 133 pm |
| 1st ionization energy | 1008 kJ/mol |
| Electron affinity | -295 kJ/mol |
| Oxidation states | -1, +1, +3, +5, +7 |
| Common ion charge | − |
| Discovered | 1811 |
Orbital diagram
Each box is one orbital holding up to two electrons of opposite spin. Following Hund’s rule, electrons spread out singly across a subshell before pairing.
Work through iodine’s configuration and its ions →
Where iodine sits
Iodine belongs to the halogens. Its Pauling electronegativity of 2.66 is mid-range; see the electronegativity chart and periodic trends for context. To use its mass in a calculation, try the molar mass calculator.
Iodine FAQ
What is the electron configuration of iodine?
Iodine (Z = 53) has the configuration 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p5. In noble-gas shorthand that is [Kr] 4d10 5s2 5p5.
How many valence electrons does iodine have?
7 (outer shell (n = 5)).
What is the atomic mass of iodine?
The standard atomic weight of iodine is 126.904 u, so one mole weighs 126.904 g.
Is iodine a metal?
No. Iodine is a halogen.
What is the charge of a iodine ion?
Iodine most commonly forms I−.