Iodine (I)

General Information

• Symbol: I
• Atomic Number: 53
• Atomic Weight: 126.90447 u
• Element Category: Halogen
• Group: 17
• Period: 5
• Block: p-block

Physical Properties

• Appearance: Shiny, dark-gray/purple-black solid
• Density: 4.933 g/cm³
• Melting Point: 113.7 °C (236.7 °F)
• Boiling Point: 184.3 °C (363.7 °F)
• Phase at STP: Solid
• Electron Configuration: [Kr] 4d¹⁰ 5s² 5p⁵
• Oxidation States: +7, +5, +1, -1 (most common)

Chemical Properties

• Reactivity: Less reactive than other halogens; reacts with metals to form iodides, and with non-metals such as phosphorus.
• Compounds: Forms compounds such as hydrogen iodide (HI), iodine monochloride (ICl), and potassium iodide (KI).

Uses and Applications

• Medicine: Used as an antiseptic (iodine tincture) and in iodine tablets for water purification. Also used in radiographic contrast media and thyroid treatments.
• Nutrition: Essential nutrient for thyroid function; added to table salt (iodized salt) to prevent iodine deficiency.
• Photography: Historically used in silver iodide for film photography.
• Chemical Reactions: Used in various chemical syntheses and as a catalyst.
• Dyes and Pigments: Used in the production of certain dyes and pigments.

Occurrence and Extraction

• Natural Occurrence: Found in trace amounts in seawater, certain minerals such as caliche, and seaweed.
• Extraction: Commercially extracted from brines, particularly in Chile and Japan, and from seaweed in smaller quantities.

Isotopes

• Stable Isotope: Iodine-127
• Radioactive Isotopes: Iodine-131 (used in medical treatments and diagnostics), Iodine-123 (used in imaging and diagnostics)

Safety and Handling

• Hazards: Toxic if ingested in large amounts; can cause skin irritation and burns. Iodine vapors are harmful if inhaled.
• Precautions: Handle with care, using appropriate protective equipment to avoid exposure.

History

• Discovery: Discovered by Bernard Courtois in 1811.
• Name Origin: Derived from the Greek word “iodes,” meaning violet, due to the color of iodine vapor.

Additional Facts

• Crystal Structure: Orthorhombic
• Magnetic Properties: Diamagnetic
• Thermal Conductivity: Low, about 0.449 W/m·K
• Electrical Resistivity: High, about 1.3×10⁷ Ω·m at room temperature

Summary

Iodine is a halogen known for its essential role in medicine, nutrition, and various industrial applications. It is less reactive than other halogens and forms compounds used in medical treatments, photography, and chemical synthesis. Found in seawater and minerals, iodine is commercially extracted from brines and seaweed. Despite its benefits, iodine is toxic in large amounts and must be handled with care.

40 Question and Answer Pairs About Iodine

1. What is the atomic number of Iodine?

   • 53

2. What is the symbol for Iodine?

   • I

3. What is the atomic weight of Iodine?

   • 126.90447 u

4. In which group of the periodic table is Iodine found?

   • Group 17

5. What period is Iodine in?

   • Period 5

6. What block does Iodine belong to?

   • p-block

7. What is the melting point of Iodine?

   • 113.7 °C (236.7 °F)

8. What is the boiling point of Iodine?

   • 184.3 °C (363.7 °F)

9. What is the density of Iodine?

   • 4.933 g/cm³

10. What is the electron configuration of Iodine?

    • [Kr] 4d¹⁰ 5s² 5p⁵

11. What are the common oxidation states of Iodine?

    • +7, +5, +1, -1

12. What is the appearance of Iodine?

    • Shiny, dark-gray/purple-black solid

13. Is Iodine reactive with air?

    • Less reactive than other halogens

14. Name a compound of Iodine.

    • Hydrogen iodide (HI)

15. What is a common use of Iodine in medicine?

    • As an antiseptic (iodine tincture)

16. How is Iodine used in nutrition?

    • Added to table salt (iodized salt) to prevent iodine deficiency

17. What role did Iodine play in photography?

    • Used in silver iodide for film photography

18. How is Iodine used in chemical reactions?

    • As a catalyst in various chemical syntheses

19. What application does Iodine have in dyes and pigments?

    • Used in the production of certain dyes and pigments

20. Name a mineral that contains Iodine.

    • Caliche

21. How is Iodine extracted from brines?

    • Commercial extraction through chemical processes

22. What is the most stable isotope of Iodine?

    • Iodine-127

23. Name a radioactive isotope of Iodine used in medical treatments.

    • Iodine-131

24. What safety hazard is associated with Iodine?

    • Toxic if ingested in large amounts

25. How should Iodine be handled?

    • With care, using appropriate protective equipment

26. Who discovered Iodine?

    • Bernard Courtois

27. Where does the name Iodine come from?

    • From the Greek word “iodes,” meaning violet

28. What is the crystal structure of Iodine?

    • Orthorhombic

29. Is Iodine paramagnetic or diamagnetic?

    • Diamagnetic

30. What is the thermal conductivity of Iodine?

    • About 0.449 W/m·K

31. What is the electrical resistivity of Iodine at room temperature?

    • About 1.3×10⁷ Ω·m

32. What is the primary oxidation state of Iodine?

    • -1

33. Is Iodine found as a free element in nature?

    • Rarely, it is usually found in compounds

34. What is the common name of potassium iodide?

    • KI

35. What is a major application of iodine monochloride (ICl)?

    • Used in organic synthesis and as a disinfectant

36. How does Iodine benefit water purification?

    • Used in iodine tablets to kill bacteria and viruses

37. What is the boiling point of Iodine in Kelvin?

    • 457.5 K

38. What group does Iodine belong to in the periodic table?

    • Halogens

39. What is the natural abundance of Iodine-127?

    • Nearly 100%

40. Can Iodine be used in high-temperature applications?

    • Yes, in specific chemical reactions and industrial processes