6. INTRO
A chemical element with the symbol ” I ” and atomic number 53
The heaviest of the stable halogens and is the least abundant
being the sixty-first most abundant element
It exists as a lustrous, purple-black non-metallic solid
at standard conditions
It melts to form a deep violet liquid at 114oC and boils to a violet
gas at 184oC
The element was discovered by the French chemist Bernard
Courtois in 1811 and was named two years later by Joseph
Louis after the Greek word “Iodes” mean "violet-coloured"
10. Iodine is the fourth halogen, being a member of group 17 in the
periodic table, below fluorine, chlorine and bromine
It has an electron configuration
of 1s2-2s2-2p6-3s2-3p6-3d10-4s2-
4p6-4d10-5s2-5p5, with the seven
electrons in the fifth and outer
most shell being its valence
electrons
It has the lowest electronegativity among halogens i.e. just 2.66
on the Pauling scale
PROPERTIES
11. PROPERTIES
General Properties
Category Property
Appearance lustrous metallic gray, violet as a gas
Standard atomic weight 126.90447
Atomic number (Z) 53
Group Group 17 (halogens)
Period period 5
Block p-block
Element category Reactive nonmetal
Electron configuration [Kr] 4d10 5s2 5p5
Electrons per shell 2, 8, 18, 18, 7
12. PROPERTIES
Physical Properties
Category Property
Phase at STP solid
Melting point (I2) 386.85 K (113.7 °C, 236.66 °F)
Boiling point (I2) 457.4 K (184.3 °C, 363.7 °F)
Density (near r.t.) 4.933 g/cm3
Triple point 386.65 K, 12.1 kPa
Critical point 819 K, 11.7 MPa
Heat of fusion (I2) 15.52 kJ/mol
Heat of vaporisation (I2) 41.57 kJ/mol
Molar heat capacity (I2) 54.44 J/(mol·K)
16. USES
About half of all produced iodine goes into various organoiodine
compounds, another 15% remains as the pure element, another 15%
is used to form potassium iodide, and another 15% for other inorganic
iodine compounds. Besides chemical use of Iodine, it is mostly used in
following major compounds
Catalysts
Animal feed supplements
Stabilisers
Dyes
Colourants and pigments
17. USES
Pharmaceutical
Sanitation (from tincture of iodine)
Photography
Minor uses of Iodine includes
Smog inhibition
Cloud seeding
Various uses in analytical chemistry
19. LAB WORK
Iodine reacts with concentrated nitric acid, forming iodic acid
I2(s) + 10 HNO3(aq) 2 HIO3(s) + 10 NO2(g) + 4 H2O(g)
Iodine does not react with oxygen or nitrogen. It does react with ozone,
O3, forming the unstable yellow I4O9
Iodine reacts with hot aqueous alkali, forming iodate IO3
−
3 I2(s) + 6 OH−(aq) IO3
−(aq) + 5 I−(aq) + 3 H2O(l)
Reaction of iodine with acids
Reaction of iodine with air
Reaction of iodine with bases
20. LAB WORK
Iodine reacts with fluorine at room temperature, forming iodine(V)
fluoride. At 250 °C the product is iodine(VII) fluoride. At -45 °C
suspension in CFCl3, iodine(III) fluoride is formed
I2(s) + 5 F2(g) 2 IF5(l) [colourless]
I2(g) + 7 F2(g) 2 IF7(g) [colourless]
I2(s) + 3 F2(g) 2 IF3(s) [yellow]
Iodine reacts with bromine forming unstable, low melting solid iodine(I)
bromide.
I2(s) + Br2(l) 2 IBr(s)
Iodine reacts with excess chlorine at -80 °C forming iodine chloride
I2Cl6. At room temperature, in the presence of water forming iodic acid
I2(s) + 3 Cl2(l) I2Cl6(s) [yellow]
I2(aq) + 6 H2O(l) + 5 Cl2(g) 2 HIO3(aq) + 10 HCl(g)
Reaction of iodine with other halogens
21. LAB WORK
Hydrogen reacts with I2 forming hydrogen iodide. The reaction is slow
at room temperature, and increases in speed with increasing
temperatures
H2(g) + Br2(g) 2 HBr(g)
Solid Cd does not react with I2(g), but will react with I2(aq). In gas
phase Cd and I2 will react forming CdI2. At high temperature and
pressure (e.g. a steel bomb) equivalent Cd and I2 will react forming CdI
Cd(s) + I2(aq) Cd2+(aq) + 2 I−(aq)
Cd(g) + I2(g) CdI2(g)
2 Cd(g) + I2(g) 2 CdI(g)
Reaction of iodine with hydrogen
Reaction of iodine with metals/ metal ions
22. LAB WORK
Iodine, I2, reacts with water, forming hypoiodite, IO−.
I2(aq) + H2O(l) IO− + 2 H+(aq) + I−(aq)
Iodine is often used as a starch indicator in science experiments.
When iodine is introduced to a substance that contains starch, it will
turn to a dark blue or blue-black hue
Reaction of iodine with water
Use of Iodine as indicator
