Element 53 · Halogen
Iodine (I) — Element 53
Greek ioeides — violet
Iodine (I) is a halogen in Period 5, Group 17 of the periodic table with atomic number 53, standard atomic weight 126.90 u, and ground-state electron configuration [Kr] 4d¹⁰ 5s² 5p⁵. At standard temperature and pressure it is classified as a solid with 7 valence electrons and common oxidation states -1, +1, +5, +7.
Disinfectants, thyroid hormone
What are the atomic properties and physical constants of Iodine?
Reference constants compiled from IUPAC standard atomic weights, the NIST Atomic Spectra Database, and the CRC Handbook.
- Atomic number (Z)
- 53
- Standard atomic mass
- 126.90 u
- Chemical family
- Halogen
- Ground-state configuration
- [Kr] 4d¹⁰ 5s² 5p⁵
- Electrons per shell
- 2, 8, 18, 18, 7
- Valence electrons
- 7
- Common ion charges / oxidation states
- -1, +1, +5, +7
- Phase at STP
- Solid
- Pauling electronegativity
- 2.66 Pauling
- First ionization energy
- 1,008 kJ/mol
- Atomic radius
- 115 pm
- Melting point
- 114 °C
- Boiling point
- 184 °C
- Discovery year
- 1811
- Table coordinate
- Period 5, Group 17
- Radioactivity
- Has stable isotope(s)
How are electrons arranged across Iodine’s shells?
A neutral Iodine atom contains 53 electrons distributed across 5 occupied principal energy shells ([Kr] 4d¹⁰ 5s² 5p⁵). The table below compares Iodine’s shell occupancy against each shell’s theoretical 2n² capacity.
| Principal Shell (n) | Spectroscopic Letter | Electrons in I | Max Shell Capacity (2n²) |
|---|---|---|---|
| n = 1 | K | 2 e⁻ | 2 e⁻ |
| n = 2 | L | 8 e⁻ | 8 e⁻ |
| n = 3 | M | 18 e⁻ | 18 e⁻ |
| n = 4 | N | 18 e⁻ | 32 e⁻ |
| n = 5 | O | 7 e⁻ | 50 e⁻ |
Frequently Asked Questions about Iodine (I)
What is the atomic mass and atomic number of Iodine (I)?
Iodine (I) has atomic number Z = 53 (53 protons in its nucleus) and an IUPAC standard atomic weight of 126.90 u. It sits in Period 5, Group 17 and is classified as a halogen.
What is the ground-state electron configuration of Iodine?
The neutral ground-state electron configuration of Iodine (Z = 53) is [Kr] 4d¹⁰ 5s² 5p⁵. Across its 5 occupied principal shells (n = 1 to n = 5), the electrons per shell are 2, 8, 18, 18, 7, with 7 valence electrons participating in bonding.
What are the common ion charges and electronegativity of Iodine?
Iodine commonly forms -1, +1, +5, +7 oxidation states or ion charges in compounds. Its Pauling electronegativity is 2.66 and its first ionization energy is 1,008 kJ/mol.
When was Iodine discovered and what is it used for?
Iodine was discovered in 1811 (Greek ioeides — violet). Disinfectants, thyroid hormone
How does Iodine compare to neighboring elements?
Other halogen elements: