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53
I
126.9
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Iodine vapor is purple. Photo by Matias Molnar.
| Classification: | Iodine is a halogen and a nonmetal |
| Atomic weight: | 126.9045 g/mol |
| Density @ 20 oC: | 4.93 g/cm3 |
| Atomic volume: | 25.74 cm3/mol |
Iodine Crystals. Photo by Ben Mills.
Discovery of Iodine
Iodine was discovered by Bernard Courtois in 1811.
He isolated the element by adding sulfuric acid to seaweed ashes.
This produced a purple vapor, which condensed to form dark crystals of iodine.
Courtois studied this new substance and found that that it combined well with phosphorous and hydrogen, but it did not form compounds easily with carbon or oxygen.
He also discovered that when mixed with ammonia it formed a brown colored solid (nitrogen triiodide) that explodes at the slightest touch.
Its name comes from the Greek work 'iodes', meaning violet.
States
State (s, l, g): solid
Melting point: 386.6 K (113.5 oC)
Melting point: 386.6 K (113.5 oC)
Boiling point: 457 K (184 oC)
Energies
Specific heat capacity: 0.214 J g-1 K-1
Heat of fusion: 15.52 kJ mol-1 of I2
1st ionization energy: 1008.4 kJ mol-1
3rd ionization energy: 3184 kJ mol-1
Heat of fusion: 15.52 kJ mol-1 of I2
1st ionization energy: 1008.4 kJ mol-1
3rd ionization energy: 3184 kJ mol-1
Heat of atomization: 107 kJ mol-1
Heat of vaporization: 41.57 kJ mol-1 of I2
2nd ionization energy: 1845.8 kJ mol-1
Electron affinity: 295.16 kJ mol-1
Heat of vaporization: 41.57 kJ mol-1 of I2
2nd ionization energy: 1845.8 kJ mol-1
Electron affinity: 295.16 kJ mol-1
Oxidation & Electrons
Shells: 2,8,18,18,7
Minimum oxidation number: -1
Min. common oxidation no.: 0
Electronegativity (Pauling Scale): 2.66
Minimum oxidation number: -1
Min. common oxidation no.: 0
Electronegativity (Pauling Scale): 2.66
Electron configuration: [Kr] 4d10 5s2 5p5
Maximum oxidation number: 7
Max. common oxidation no.: 7
Polarizability volume: 5 Å3
Maximum oxidation number: 7
Max. common oxidation no.: 7
Polarizability volume: 5 Å3
Appearance & Characteristics
Structure: layers of I2
Hardness: mohs
Hardness: mohs
Chemical clock reactions - amazing color changes.
Iodine crystals sublimate (turn from solid to gas without becoming liquid) and then freeze back to solid iodine.
Color: bluish-black solid, purple vapor
Harmful effects:
In small doses, iodine is slightly toxic and it is highly poisonous in large amounts. Elemental iodine is an irritant which can cause sores on the skin. Iodine vapor causes extreme eye irritation.
Characteristics:
Iodine is a bluish-black, lustrous solid. Although it is less reactive than the elements above it in group 17 (fluorine, chlorine and bromine) it still forms compounds with many other elements.
Although iodine is a non-metal, it displays some metallic properties.
When dissolved in chloroform, carbon tetrachloride or carbon disulphide, Iodine yields purple colored solutions. It is barely soluble in water, giving a yellow solution.
Uses:
Iodine is important in medicine, in both radioactive and non-radioactive forms. Iodide and thyroxin, which contains iodine, are used inside the body.
A solution containing potassium iodide (KI) and iodine in alcohol is used to disinfect external wounds. Elemental iodine is also used as a disinfectant.
Silver iodide is used in photography.
Iodine is sometimes added to table salt to prevent thyroid disease.
Iodine's other uses include catalysts, animal feeds and printing inks and dyes.
Harmful effects:
In small doses, iodine is slightly toxic and it is highly poisonous in large amounts. Elemental iodine is an irritant which can cause sores on the skin. Iodine vapor causes extreme eye irritation.
Characteristics:
Iodine is a bluish-black, lustrous solid. Although it is less reactive than the elements above it in group 17 (fluorine, chlorine and bromine) it still forms compounds with many other elements.
Although iodine is a non-metal, it displays some metallic properties.
When dissolved in chloroform, carbon tetrachloride or carbon disulphide, Iodine yields purple colored solutions. It is barely soluble in water, giving a yellow solution.
Uses:
Iodine is important in medicine, in both radioactive and non-radioactive forms. Iodide and thyroxin, which contains iodine, are used inside the body.
A solution containing potassium iodide (KI) and iodine in alcohol is used to disinfect external wounds. Elemental iodine is also used as a disinfectant.
Silver iodide is used in photography.
Iodine is sometimes added to table salt to prevent thyroid disease.
Iodine's other uses include catalysts, animal feeds and printing inks and dyes.
Reactions & Compounds
Reaction with air: none
Reaction with 15 M HNO3: mild, ⇒ HIO3
Oxide(s): I2O5, I4O9, I2O4
Hydride(s): HI
Reaction with 15 M HNO3: mild, ⇒ HIO3
Oxide(s): I2O5, I4O9, I2O4
Hydride(s): HI
Reaction with 6 M HCl: none
Reaction with 6 M NaOH: mild, ⇒ OI-, I-
Chloride(s): ICl, ICl3
Reaction with 6 M NaOH: mild, ⇒ OI-, I-
Chloride(s): ICl, ICl3
Radius
Atomic radius: 140 pm
Ionic radius (2+ ion): pm
Ionic radius (2- ion): pm
Ionic radius (2+ ion): pm
Ionic radius (2- ion): pm
Ionic radius (1+ ion): pm
Ionic radius (3+ ion): pm
Ionic radius (1- ion): 206 pm
Ionic radius (3+ ion): pm
Ionic radius (1- ion): 206 pm
Conductivity
Thermal conductivity: 0.45 W m-1 K-1
Electrical conductivity: 1.0 x 10-7 S cm-1
Abundance & Isotopes
Abundance earth's crust: 450 parts per billion by weight, 73 parts per billion by moles
Abundance solar system: parts per billion by weight, parts per billion by moles
Cost, pure: $8.3 per 100g
Cost, bulk: $ per 100g
Source: In nature, iodine occurs in the form of iodide ions, mainly in seawater. It is introduced into the food chain via seaweed and other sea-plants. Iodine is found in some minerals and soils.
Commercially, iodine is obtained in several ways, such as taking iodine vapour from processed brine, by ion exchange of brine or by releasing iodine from iodate taken from nitrate ores.
Isotopes: 34 whose half-lives are known, with mass numbers 108 to 141. Of these, only one is stable: 127I
Abundance solar system: parts per billion by weight, parts per billion by moles
Cost, pure: $8.3 per 100g
Cost, bulk: $ per 100g
Source: In nature, iodine occurs in the form of iodide ions, mainly in seawater. It is introduced into the food chain via seaweed and other sea-plants. Iodine is found in some minerals and soils.
Commercially, iodine is obtained in several ways, such as taking iodine vapour from processed brine, by ion exchange of brine or by releasing iodine from iodate taken from nitrate ores.
Isotopes: 34 whose half-lives are known, with mass numbers 108 to 141. Of these, only one is stable: 127I
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