碘 uses the stone radical 石 on the left (since it was classified among mineral-like substances) and the phonetic component 典. The character sounds just like 点. Remember: iodine is element number 53, and it's a key 'point' in nutrition.
石 (the stone radical) is used here in the chemistry-element sense. Many non-metal elements were given 石-radical chars to mark them as mineral-derived. Iodine 碘, silicon 硅, sulfur 硫, phosphorus 磷, boron 硼 all share this naming pattern.
典 provides the sound directly. 碘 was coined for iodine in early 20th-century chemistry vocabulary, choosing a phonetic match for the iodo-/I- sound rather than carrying any of 典's classical-canon meaning.
