Which of the following best describes the Lewis structure of $P_{I}3$ (phosphorus triiodide)?

• A. Phosphorus is bonded to three iodine atoms in a linear arrangement with two lone pairs on phosphorus.
• B. Phosphorus is the central atom with three single bonds to iodine atoms and no lone pairs on phosphorus.
• C. Phosphorus is the central atom with three double bonds to iodine atoms and no lone pairs on phosphorus.
• D. Phosphorus is the central atom with three single bonds to iodine atoms and one lone pair on phosphorus.

Answer: (D)

Verified step by step guidance

1. Identify the central atom in phosphorus triiodide (PI\_3). Phosphorus (P) is less electronegative than iodine (I), so phosphorus will be the central atom.
2. Determine the number of valence electrons for each atom: phosphorus has 5 valence electrons, and each iodine has 7 valence electrons. Since there are three iodine atoms, total valence electrons = 5 + 3 \times 7 = 26 electrons.
3. Draw single bonds between phosphorus and each iodine atom. Each single bond accounts for 2 electrons, so 3 bonds use 6 electrons, leaving 20 electrons to be distributed as lone pairs.
4. Distribute the remaining electrons to satisfy the octet rule. Place lone pairs on the iodine atoms first to complete their octets (each iodine needs 6 more electrons after bonding). Then place any leftover electrons as lone pairs on phosphorus.
5. Check the formal charges and the octet rule for all atoms. Phosphorus will have one lone pair and three single bonds to iodine atoms, which satisfies the octet rule and results in the most stable Lewis structure.