Iodine (I)
Element 53 · Halogen · Solid at 25 °C · Group 17, Period 5
Iodine is essential to your thyroid — the reason table salt is iodized — and famous for a solid that sublimes into violet vapor.
On the periodic table, iodine sits in group 17 — the halogens — in period 5. It is one of 6 elements classified as a halogen, and at room temperature (25 °C) it is a solid.
The halogens of group 17 are one electron short of a full outer shell, which makes them ferociously good at grabbing electrons from other elements. Their name means “salt-former”: they combine with metals to make salts such as sodium chloride. They exist as diatomic molecules, and the group is the only one to span gas, liquid, and solid at room temperature. Reactivity decreases down the group.
Properties of iodine
| Atomic number (Z) | 53 |
|---|---|
| Symbol | I |
| Atomic mass | 126.90 |
| Category | Halogen |
| Group | 17 |
| Period | 5 |
| Block | p-block |
| Metal / nonmetal | Nonmetal |
| State at 25 °C | Solid |
| Electron configuration | [Kr] 4d10 5s2 5p5 |
| Electronegativity (Pauling) | 2.66 |
| Melting point | 113.7 °C (386.85 K / 236.66 °F) |
| Boiling point | 184.3 °C (457.45 K / 363.74 °F) |
| Density | 4.933 g/cm³ |
Position in the periodic table
Iodine shares group 17 — the halogens with Fluorine (F), Chlorine (Cl), Bromine (Br), Astatine (At), Tennessine (Ts). Elements in the same group have the same number of outer electrons, so they tend to behave alike chemically — comparing them is one of the fastest ways to see periodic trends in action.
Within this dataset, it ranks #7 in electronegativity out of 99 elements with a pauling value.
Physical properties
Iodine melts at 113.7 °C (386.85 K / 236.66 °F) and boils at 184.3 °C (457.45 K / 363.74 °F), giving it a liquid range of about 70.6 °C at standard pressure.
Its density is 4.933 g/cm³.
See also: the interactive periodic table, how to read the periodic table, the element families tour.