Iodine (I)

Dark gray or purple-black solid

Iodine is a purple-black solid that sublimes into violet vapor and is essential for thyroid function, and as the heaviest stable halogen, iodine has the lowest electronegativity (2.66) and largest atomic radius. Thyroid hormones T3 and T4 contain 3 and 4 iodine atoms respectively, regulating metabolism.

Key metrics

Density4.93g/cm³

Melting point387K

Boiling point457K

Electronegativity2.66Pauling

Discovery

1811discovered

Discovered by: Bernard Courtois
Reactivity profile: Reactive halogen
Reactivity: Medium
Bonding: Covalent

Electron configuration

\textcolor{#6b7280}{[Kr]}\; \textcolor{#22c55e}{4_{d}^{10}}\; \textcolor{#ef4444}{5_{s}^{2}}\; \textcolor{#3b82f6}{5_{p}^{5}}

[Kr] 4d10 5s2 5p5

Wave function

\Psi_{\text{I}} \approx \frac{1}{\sqrt{53!}} \det \left| \chi_1(\mathbf{r}_1) \dots \chi_{53}(\mathbf{r}_{53}) \right|

Probability density $|\Psi|^2$ across the I valence shell.

Crystal structure

Orthorhombic

Lattice constantsa 1.00 · b 1.30 · c 0.90

Cell anglesα = β = γ = 90°

Coordination number—

Atoms per cell—

Atomic packing factor0.60

Physical properties

Atomic radius: 115 pm
Ionization energy: 1008 kJ/mol
Electron affinity: 295 kJ/mol
Crystal structure: Orthorhombic

Oxidation states

-1+1+5+7

Acid/base

Acidic

Strongly acidicStrongly basic

State at 25 °CSolid

387 K457 K298 K

Emission spectrum

3 transitions

380450500550600650700780

VioletBlueGreenYellowRed

516.1nmI I (green)Green100%

546.4nmI I (green)Green70%

589.3nmI I (yellow)Yellow50%

Dominant line 516.1 nmRange 516–589 nmTransitions 3