Iodine

53
I
Group
17
Period
5
Block
p
Protons
Electrons
Neutrons
53
53
74
General Properties
Atomic Number
53
Atomic Weight
126.90447
Mass Number
127
Category
Halogens
Color
Slate Gray
Radioactive
No
From the Greek word iodes, violet
Crystal Structure
Base Centered Orthorhombic
History
Iodine was discovered by French chemist Bernard Courtois in 1811.

He treated the liquor obtained from the extraction of kelp, with sulfuric acid to produce a vapour with a violet color.

In 1812, Joseph Louis Gay-Lussac demonstrated that iodine was an element and its chemical relationship to chlorine.
Electrons per shell
2, 8, 18, 18, 7
Electron Configuration
[Kr] 4d10 5s2 5p5
I
Kelp was the main source of natural iodine in the 18th and 19th centuries
Physical Properties
Phase
Solid
Density
4.93 g/cm3
Melting Point
386.85 K | 113.7 °C | 236.66 °F
Boiling Point
457.4 K | 184.25 °C | 363.65 °F
Heat of Fusion
7.76 kJ/mol
Heat of Vaporization
20.9 kJ/mol
Specific Heat Capacity
0.214 J/g·K
Abundance in Earth's crust
0.000049%
Abundance in Universe
1×10-7%
Pure
Image Credits: Images-of-elements
Pure crystalline iodine
CAS Number
7553-56-2
PubChem CID Number
807
Atomic Properties
Atomic Radius
140 pm
Covalent Radius
139 pm
Electronegativity
2.66 (Pauling scale)
Ionization Potential
10.4513 eV
Atomic Volume
25.74 cm3/mol
Thermal Conductivity
0.00449 W/cm·K
Oxidation States
-1, 1, 3, 5, 7
Applications
Iodine compounds are important in organic chemistry and very useful in medicine.

A solution containing potassium iodide and iodine in alcohol is used to disinfect external wounds.

Silver iodide is a major ingredient to traditional photographic film.

Iodine is added to table salt to prevent thyroid disease.
Elemental iodine is toxic if taken orally
Isotopes
Stable Isotopes
127I
Unstable Isotopes
108I, 109I, 110I, 111I, 112I, 113I, 114I, 115I, 116I, 117I, 118I, 119I, 120I, 121I, 122I, 123I, 124I, 125I, 126I, 128I, 129I, 130I, 131I, 132I, 133I, 134I, 135I, 136I, 137I, 138I, 139I, 140I, 141I, 142I, 143I, 144I