Why is Iodine a Halogen? (+ 3 More Things to Know)

Yes, iodine is a halogen. Iodine is a halogen because it belongs to Group 17 (Group VIIA) of the periodic table, which is known as the halogen group. It shares common characteristics with other halogens, such as having seven valence electrons and a high reactivity. 1

Well, this was just a simple answer. But there are few more things to know about this topic which will make your concept super clear.

So let’s dive right into it.

Key Takeaways: Why is Iodine a Halogen?

  • Iodine is a halogen because it belongs to Group 17 (Group VIIA) of the periodic table.
  • Iodine has several properties that classify it as a halogen, including its electronic configuration, reactivity, electronegativity, and halogen displacement reactions.
  • While iodine shares many similarities with other halogens, it also exhibits some distinct differences, such as its physical state, density, melting and boiling points, reactivity, and biological significance.

Explanation: Why is iodine a halogen?

Iodine is classified as a halogen due to its position in the periodic table. Halogens are a group of highly reactive nonmetals that occupy Group 17 of the periodic table. 2 Iodine exhibits similar chemical properties to other halogens such as chlorine, bromine, and fluorine, making it fittingly categorized as a halogen.

The classification of iodine as a halogen is based on its electronic configuration and chemical behavior. In the periodic table, elements in the same group tend to have similar properties due to their shared outer electron configuration. 3

Halogens have seven valence electrons, resulting in a high reactivity and a tendency to form compounds by gaining one electron to achieve a stable, full outer electron shell. 4

Iodine exhibits these characteristics, reacting readily with other elements and compounds to form various iodides. Its classification as a halogen allows for a better understanding of its chemical behavior and its similarities to other elements in the same group.

Properties of iodine that classify it as a halogen

There are several properties of iodine that classify it as a halogen:

  • Valence electrons: Iodine, like other halogens, has seven valence electrons in its outermost energy level. This electron configuration makes it highly reactive and prone to forming compounds by gaining one electron to achieve a stable, full outer electron shell.
  • Electronegativity: Iodine has a relatively high electronegativity, which means it has a strong attraction for electrons. This property allows iodine to readily form covalent bonds with other elements, particularly those that can donate an electron.
  • Reactivity: Iodine is a highly reactive element. It readily reacts with other substances, such as metals, nonmetals, and organic compounds. This reactivity is characteristic of halogens and is attributed to their strong desire to gain an electron to achieve a stable electron configuration. 5
  • Halogen displacement reactions: Iodine can displace other halogens from their compounds in certain reactions. This property is a hallmark of halogens and is commonly observed in chemical reactions involving iodine and other halides.
  • Diatomic molecule: Like other halogens, iodine exists as a diatomic molecule, I2, in its elemental form. The I2 molecule consists of two iodine atoms covalently bonded together, forming a stable molecule. 6 7

These properties collectively demonstrate the similarities between iodine and other halogens, further supporting its classification as a member of the halogen group.

How is iodine different from other halogens?

While iodine shares many similarities with other halogens, there are a few key differences that set it apart:

  • Physical state: Unlike the other halogens (fluorine, chlorine, bromine, and astatine), iodine is a solid at room temperature and atmospheric pressure. 8 Fluorine and chlorine are gases, bromine is a liquid, and astatine is a solid but is very rare.
  • Density: Iodine is denser than the lighter halogens such as fluorine, chlorine, and bromine. This higher density is due to the larger atomic size of iodine.
  • Melting and boiling points: Iodine has a higher melting point and boiling point compared to the lighter halogens. 9 This is because the intermolecular forces, known as van der Waals forces, become stronger with increasing atomic size. As a result, iodine exists as a solid at room temperature, while the lighter halogens are gases or liquids.
  • Reactivity: Iodine is less reactive than the other halogens. 10 While iodine can still undergo various chemical reactions, it generally reacts more slowly compared to fluorine, chlorine, and bromine. This lower reactivity is attributed to the larger atomic size of iodine, which makes it less likely to attract an additional electron and form compounds.
  • Biological significance: Iodine is unique among the halogens in its essential role in human health. It is necessary for the production of thyroid hormones, which regulate metabolism. Fluorine, chlorine, bromine, and astatine do not play a similar vital role in human physiology. 11 12

These differences highlight the distinct characteristics of iodine and demonstrate how it deviates from the typical properties exhibited by other halogens.

Further reading

Why are Halogens So Reactive?
Does water conduct electricity?
Why is Cobalt Magnetic?
Is Aluminum Magnetic?
Is Copper Magnetic?

About author

Jay is an educator and has helped more than 100,000 students in their studies by providing simple and easy explanations on different science-related topics. He is a founder of Pediabay and is passionate about helping students through his easily digestible explanations.

Read more about our Editorial process.


  1. Boudreaux, K. A. (n.d.). The Parts of the Periodic Table. The Parts of the Periodic Table. https://www.angelo.edu/faculty/kboudrea/periodic/periodic_main7.htm
  2. The Chemistry of the Halogens. (n.d.). The Chemistry of the Halogens. https://chemed.chem.purdue.edu/genchem/topicreview/bp/ch10/group7.php
  3. 2.6: The periodic trends in properties of the elements. (2022, April 4). Chemistry LibreTexts. https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Introduction_to_General_Chemistry_(Malik)/02%3A_Elements/2.06%3A_The_periodic_trends_in_properties_of_the_elements
  4. Foundation, C. (n.d.). Welcome to CK-12 Foundation | CK-12 Foundation. Welcome to CK-12 Foundation | CK-12 Foundation. https://www.ck12.org/section/electron-configuration-and-the-periodic-table-::of::-the-periodic-table-::of::-ck-12-chemistry-basic/
  5. Iodine – Wikipedia. (2017, November 20). Iodine – Wikipedia. https://en.wikipedia.org/wiki/Iodine
  6. Boudreaux, K. A. (n.d.). The Parts of the Periodic Table. The Parts of the Periodic Table. https://www.angelo.edu/faculty/kboudrea/periodic/physical_diatomics.htm
  7. 17.4B: Dichlorine, Dibromine, and Diiodine. (2015, June 21). Chemistry LibreTexts. https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Map%3A_Inorganic_Chemistry_(Housecroft)/17%3A_The_Group_17_Elements/17.04%3A_The_Elements/17.4B%3A_Dichlorine_Dibromine_and_Diiodine
  8. Iodine – Molten State, Lewis Complexes, Oxidation States, Reducing Agent. (n.d.). Encyclopedia Britannica. https://www.britannica.com/science/iodine
  9. Appendix 2: The Elements: Symbols, Melting Points, Boiling Points, Densities, and Electronegativities. (n.d.). Ionic Compounds, 169–170. https://doi.org/10.1002/0470075104.app2
  10. L. (2017, April 19). Facts About Iodine. livescience.com. https://www.livescience.com/37441-iodine.html
  11. Iodine. (2021, October 19). The Nutrition Source. https://www.hsph.harvard.edu/nutritionsource/iodine/
  12. Fuge, R., & Johnson, C. C. (2015, December). Iodine and human health, the role of environmental geochemistry and diet, a review. Applied Geochemistry, 63, 282–302. https://doi.org/10.1016/j.apgeochem.2015.09.013

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top