Iodine forms which ion?

Iodine forms which ion?

• A. I -
• B. I 2-
• C. I 0
• D. I +

Answer: (A)

Iodine is a halogen and tends to gain electrons to complete its outer shell. With seven valence electrons, it needs one more to reach a full octet, so it forms the iodide ion, I−. This -1 charge reflects gaining one electron, which is exactly what gives iodine its common ionic form in salts like KI. The neutral iodine atom (I0) or diatomic iodine (I2) are not ions, and a positively charged iodine ion (I+) would require removing electrons, which halogens don’t do in typical chemistry. I2− would be an unusual, unstable dianion. So the stable ion formed is I−.

Iodine is a halogen and tends to gain electrons to complete its outer shell. With seven valence electrons, it needs one more to reach a full octet, so it forms the iodide ion, I−. This -1 charge reflects gaining one electron, which is exactly what gives iodine its common ionic form in salts like KI. The neutral iodine atom (I0) or diatomic iodine (I2) are not ions, and a positively charged iodine ion (I+) would require removing electrons, which halogens don’t do in typical chemistry. I2− would be an unusual, unstable dianion. So the stable ion formed is I−.