What is the Valency of Iodine?

The primary and most common valency of Iodine is 1.

The concept of valency depends entirely on the outermost shell (valence shell) of an atom.

• The outermost shell of Iodine has exactly 7 valence electrons (s² p⁵ configuration).
• According to the Octet Rule, every atom wants to have 8 electrons in its outer shell to become stable like a noble gas.
• Since Iodine already has 7, it only needs to gain or share 1 more electron to reach 8. Therefore, its combining capacity (valency) is 1.

Because its valency is 1, it usually forms simple compounds by gaining one electron to form an Iodide ion (I⁻), or by sharing one electron.

• Potassium Iodide (KI): Potassium gives 1 electron, Iodine takes 1.
• Hydrogen Iodide (HI): Hydrogen and Iodine share 1 electron each.

While its primary valency is 1, Iodine is a large atom located lower down in the periodic table. It has empty 'd-orbitals' available. Because of this, it can 'expand its octet' and share more electrons when it reacts with highly electronegative elements (like Oxygen or Fluorine). Therefore, Iodine can also show variable valencies of 3, 5, and 7 in specific advanced compounds (e.g., IF₇ - Iodine Heptafluoride, where its valency is 7).