Iodine dissolves in a solution of potassium iodide as the triiodide ion, I₃⁻.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Iodine dissolves in a solution of potassium iodide as the triiodide ion, . Count its valence electrons. With the atoms in a row and single bonds, how many lone pairs sit on the middle iodine, and what is its formal charge?
Need a reminder? The key ideaShow
Formal charge . The best structure has the smallest formal charges, puts a negative charge on the most electronegative atom, and has no like charges side by side. Only atoms from period 3 down can hold more than eight electrons.
The worked solution
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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Electrons. .
Step 2. Place them. Two bonds use . The two end iodines take three lone pairs each, more. The last make three lone pairs on the middle iodine.
Step 3. Formal charge. Middle: . Each end: .
Answer: electrons; lone pairs; formal charge on the middle iodine, which holds electrons.
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