Iodine (I)
Halogen · p-block · period 5 · group 17
Shiny, blue-black solid that sublimes to a violet vapour.
Iodine (symbol I) is chemical element number 53, a halogen in group 17, period 5 of the periodic table. Its standard atomic weight is 126.90 and its electron configuration is [Kr] 4d10 5s2 5p5. At room temperature it is a solid. Its name is Greek for 'violet', the colour of its vapour.
Properties
| Atomic number | 53 |
|---|---|
| Atomic mass | 126.90 |
| Category | Halogen |
| Block | p-block |
| Group · Period | 17 · 5 |
| Electron configuration | [Kr] 4d10 5s2 5p5 |
| Electrons per shell | 2, 8, 18, 18, 7 |
| State at 25 °C | solid |
| Melting point | 386.85 K |
| Boiling point | 457.4 K |
| Density | 4.933 g/cm³ |
| Electronegativity (Pauling) | 2.66 |
| Radioactive | No |
| Origin | primordial |
| Discovered | 1811 · Bernard Courtois |
Key facts about Iodine
- Its name is Greek for 'violet', the colour of its vapour.
- Your thyroid gland needs iodine to make its hormones; a shortage causes goitre.
- That is why table salt is 'iodised'.
- Tincture of iodine has been a wound antiseptic for over 150 years.
What Iodine is used for
Iodised salt, antiseptics, X-ray contrast media, photographic chemicals, LCD polarising films, catalysts.
Where it sits in the periodic table
Iodine is in group 17, period 5, of the p-block. Its electron configuration [Kr] 4d10 5s2 5p5 means its outermost shell holds 7 electrons, which is what places it here and explains much of its chemistry. See Iodine on the interactive table →
Iodine — frequently asked questions
What is Iodine used for?
Iodised salt, antiseptics, X-ray contrast media, photographic chemicals, LCD polarising films, catalysts.
Is Iodine radioactive?
No. Iodine has at least one stable isotope and is not radioactive.
What is the electron configuration of Iodine?
Iodine has the electron configuration [Kr] 4d10 5s2 5p5, which is 2, 8, 18, 18, 7 electrons per shell.
What group and period is Iodine in?
Iodine is in group 17, period 5, in the p-block. Its outer shell holds 7 electrons.
Who discovered Iodine?
Iodine was discovered in 1811 by Bernard Courtois.