* Protons: The number of protons is determined by the atomic number of the element. Iodine (I) has an atomic number of 53. Therefore, an iodide ion has 53 protons.
* Electrons: Ions form when atoms gain or lose electrons. A neutral iodine atom has 53 electrons. The negative charge on the iodide ion (I⁻) indicates it has gained one electron. So, an iodide ion has 54 electrons.
