Please explain the Lewis structure of the I3- ion, which is hypervalent. Where do we obtain ions and all things in this way?
The correct answer and explanation is:
Correct Answer:
The Lewis structure of the triiodide ion (I₃⁻) consists of three iodine atoms with a negative one charge, arranged linearly. The central iodine atom forms single bonds with the two outer iodine atoms and carries three lone pairs of electrons, making it hypervalent.
Detailed Explanation:
To understand the Lewis structure of I₃⁻ (triiodide ion), begin by counting the total number of valence electrons. Each iodine atom has 7 valence electrons, so three iodine atoms give 21 electrons. Additionally, the negative charge adds one extra electron, making the total 22 valence electrons.
The structure is linear: I–I–I⁻. The central iodine atom connects to the two outer iodine atoms with single bonds. Each single bond uses 2 electrons, totaling 4 electrons. Subtracting this from 22 gives 18 electrons remaining. These are placed as lone pairs to complete the octets of the outer iodine atoms first, and then the remaining pairs are placed on the central iodine.
Each outer iodine gets three lone pairs (6 electrons each), consuming 12 electrons. Now 6 electrons remain, which are assigned as three lone pairs to the central iodine atom. As a result, the central iodine has 10 electrons around it: two from each bond and six from the lone pairs. This is more than the typical octet, which is why the ion is considered hypervalent. Hypervalency is possible in elements from period 3 or higher, like iodine, because they can use d-orbitals to accommodate extra electrons.
The ion exists because iodine is electronegative and can stabilize extra electrons. The triiodide ion is commonly found in solutions of iodine and iodide, such as in Lugol’s iodine. Ions like these arise from redox reactions and are stabilized in polar solvents or crystal lattices.
In summary, the I₃⁻ ion is linear and hypervalent due to expanded octet on the central iodine, made possible by its position in the periodic table and the nature of iodine bonding.