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Iodine

Element 53 · Halogen

Specimen

Atomic number
53
Atomic mass
126.9
State at room temperature
Solid
Melting point
113.7 °C
Boiling point
184.4 °C
Density
4.93 g/cm³
Discovered
1811

Atomic mass from IUPAC.1 Other physical data from PubChem.2

Can I eat it?

In food and water
Your body needs it. Iodine, as iodide in food and iodized salt, is a nutrient. The thyroid uses it to make hormones. EFSA sets an adequate intake of 150 micrograms a day for adults. Too little iodine causes goiter. 34

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The atom

I
ShellElectrons
1 (K) 2
2 (L) 8
3 (M) 18
4 (N) 18
5 (O) outermost 7
Total53

Configuration [Kr] 4d¹⁰ 5s² 5p⁵

4d ↑ ↓ ↑ ↓ ↑ ↓ ↑ ↓ ↑ ↓
5s ↑ ↓
5p ↑ ↓ ↑ ↓ ↑
A shell diagram: each ring is an electron shell and each dot is one electron. The nucleus holds 53 protons. The outermost shell is shown in red. Electrons do not travel on rings: they fill orbitals, regions where an electron is likely to be found. The boxes are those orbitals for the electrons outside the Kr core, with one arrow per electron.

Related elements

Group 17
F Fluorine Cl Chlorine Br Bromine At Astatine Ts Tennessine

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Sources

  1. 1

    IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW), 2024. Abridged Standard Atomic Weights 2024 .

    The atomic mass shown for the 84 elements that have a standard atomic weight.

  2. 2

    National Center for Biotechnology Information (PubChem), 2026. Periodic Table of Elements .

    Electron configuration, melting and boiling points, density and discovery year for all 118 elements.

  3. 3

    European Food Safety Authority (EFSA), 2017. Dietary Reference Values for nutrients. Summary report , Section 4.5 (iodine) and 4.9 (molybdenum).

    • Iodine is an essential nutrient for mammals, required as a mandatory structural and functional element of thyroid hormones ... an Adequate Intake (AI) for iodine for adult men and women can be set at 150 µg/day
  4. 4

    Royal Society of Chemistry, 2026. Iodine - Element information, properties and uses .

    • A deficiency of iodine can cause the thyroid gland to swell up (known as goitre).
  5. 5

    National Institute of Standards and Technology (NIST), 2026. Atomic Weights and Isotopic Compositions for All Elements .

    Isotopic composition of each element; the most abundant isotope sets the neutron count in the nucleus view.