Iodine (I): Electron Configuration, Properties and Uses
Iodine (I): Electron Configuration, Properties and Uses
Electron configuration [Kr] 5s2 4d10 5p5 · group 17 · period 5 · Ar 126.9
Iodine data
- Atomic number
- 53
- Relative atomic mass
- 126.9
- Group
- 17
- Period
- 5
- Block
- p
- Category
- Halogen
- Electron configuration
- [Kr] 5s2 4d10 5p5
- Full configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p5
- Electrons per shell
- 2, 8, 18, 18, 7 (K L M N O)
- Valence electrons
- 7
- Electronegativity (Pauling)
- 2.66
- First ionisation energy
- 10.451 eV
- Atomic radius (van der Waals)
- 198 pm
- State at room temperature
- Solid
- Melting point
- 114 °C
- Boiling point
- 184 °C
- Density
- 4.93 g/cm³
- Common oxidation states
- +7, +5, +1, −1
- Discovered
- 1811
Source: PubChem (NIH, accessed 13 Nov 2026); atomic mass: IUPAC standard atomic weight.
Electron shell diagram
K 2 · L 8 · M 18 · N 18 · O 7
Orbital diagram (outer electrons)
About iodine
Iodine, symbol I, is element number 53 in the periodic table. It is a halogen in group 17, period 5, p-block. The element was discovered in 1811. Iodine is a solid at room temperature, melting at 114 °C and boiling at 184 °C.
Iodine electron configuration
The electron configuration of iodine is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p5, or in short [Kr] 5s2 4d10 5p5. Its electrons occupy 5 shells: K = 2, L = 8, M = 18, N = 18, O = 7. Iodine has 7 valence electrons in the O shell (5s2 5p5), which is why it sits in group 17. In ionic compounds iodine gains electrons to fill its outer shell: I− = [Xe] (like xenon).
Filling order: 1s2(2) → 2s2(4) → 2p6(10) → 3s2(12) → 3p6(18) → 4s2(20) → 3d10(30) → 4p6(36) → 5s2(38) → 4d10(48) → 5p5(53)
Uses of iodine
Well-known applications of iodine include povidone-iodine antiseptic, iodised salt against goitre, X-ray contrast agents and iodometric titration. For research and analysis you can browse iodide compounds in the AMI Scientific catalogue.
Safety
Iodine vapour irritates the eyes and airways, and solid iodine stains skin brown. Always read the safety data sheet (SDS) before working with a chemical.
Other elements in group 17
Frequently asked questions
What is the electron configuration of iodine?
The electron configuration of iodine (I, atomic number 53) is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p5, or [Kr] 5s2 4d10 5p5 in short. By shell: 2, 8, 18, 18, 7.
How many valence electrons does iodine have?
Iodine has 7 valence electrons.
Which group and period is iodine in?
Iodine is in group 17, period 5, p-block.
What is the atomic mass of iodine?
The relative atomic mass of iodine is 126.9. Use it to calculate molar mass with the molar mass calculator.
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