5. Lewis Structure of I₃^-.

1. Count the total number of valence shell (N_T) for all the atoms in this anion.(compute the negative charge).

	Wrong. Check the valence shell electrons for I atoms and include the negative charge.
	Right 7 electrons for each I plus the negative charge. Total 22 electrons
	Wrong. Check the valence shell electrons for I atoms and include the negative charge.

2. How many electrons are used in the single bonds.

	Wrong. The I atom is bonded to two more atoms. That requires more than 2 electrons.
	Right. One I is linked to the other two atoms. That requieres 4 electrons

3. How many additional electrons need the terminal I atoms?.

	Wrong. Each terminal I atoms would complete only 7 electrons.
	Right. Each I atom is sharing 2 electrons with the atom. Need 6 more to reach a shell of eight electrons. So the total number will 12 electrons
	Wrong. That would represent a total of 9 electrons around each terminal I atom.

4. How many additional electrons need the central atom?

	Right. The central atom shares 2 electrons with each terminal atoms. It needs 4 electrons more to complete the 8 electrons shell.
	Wrong. In principle the central I atom only needs four additional electrons. However see later.

5 Two electrons are not located. What is the best location for them?

On the central I atom	Right. The central I atom can expand the eight electron shell and get a 10 electronesenvironment..
On the terminal I atoms.	Wrong. Terminal atoms cannot expand the eight electron shell.

6. What is the geometry of this anion? Structures

	Wrong. The central atom has a AE₃X₂ environment. That requires five positions around the central atom to locate the five electron pairs. Find the best location for the three unshared electron pairs. The angular geometry does not minimize the electronic repulsion.
	Right The three electron pairs of the central atom are separated by angles of 120°The five electron pair form a trigonal-bipyramide.

5. Lewis Structure of I3-.