Fun Facts about Iodine: Properties, Uses, and Historical Insights

Fun Facts About the Element Iodine

Physical Properties

Iodine does not simply sublimate at atmospheric pressure as often taught. Instead, between 114 °C and 184 °C, it exists as a dark violet liquid. Solid iodine is grey, while its vapor and liquid forms show a violet hue. This element is solvatochromic—its color changes depending on the solvent. For example, in water, iodine appears yellowish-brown, but in alcohols like ethanol or 1-butanol, it shifts to a reddish-brown shade.

Biological Importance

Iodine is vital for thyroid gland function. A lack of iodine in the diet causes thyroid failure. This is why iodized salt is widely used to prevent iodine deficiency. Seaweed, a common ingredient in sushi, provides a natural source of iodine, supporting thyroid health.

Uses and Applications

• Radiation Protection: Potassium iodide protects the thyroid gland from radioactive iodine during nuclear emergencies.
• Radiation Detectors: Iodine compounds serve in scintillators used to detect radiation.
• Chemical Industry: Iodine participates in palladium-catalyzed cross-coupling reactions and radical chemistry due to its easy abstraction from substrates.
• Semiconductors: Iodine improves conductivity in porous semiconductor materials.
• Cloud Seeding: Silver iodide crystals stimulate condensation in clouds to induce rain.

Unique Laboratory Observations

Heating iodine crystals produces a striking violet vapor. It dissolves in alkali and potassium iodide solution, forming the brown triiodide (I3-) ion, as found in Lugol’s solution. Adding hydrochloric acid to iodine dissolved in sodium hydroxide releases violet iodine vapor, a dramatic but fume hood–required demonstration.

Historical Note

Notably, iodine’s symbol was “J” on the Soviet periodic table, differing from the modern “I.”

Key Takeaways

• Iodine shows varied colors due to solvatochromism and phase changes.
• It is essential for thyroid function and widely used in iodized salt.
• Applications range from radiation protection to semiconductors and cloud seeding.
• Laboratory experiments with iodine produce distinctive violet vapors.
• Its historical symbol “J” differs from the modern “I.”