Lewis structure of I₃⁻
22 valence electrons. Two I-I single bonds, with three lone pairs on I, so I has 10 electrons around it (an expanded octet).
Lewis structure
22 valence electronsFormal charges: I −1
Why this shape
- The central I has 7 valence electrons. In the Lewis structure it makes two single bonds to I and keeps three lone pairs, which leaves it a formal charge of −1.
- Steric number = two sigma bonds + three lone pairs = 5, so the central I is sp³d hybridised.
- Five electron pairs point to the corners of a trigonal bipyramid (trigonal bipyramidal electron geometry). With three lone pairs in place of atoms, the atoms make a linear shape.
- All three lone pairs take the equatorial positions, 120 degrees apart, and the two bonds point up and down.
- The lone pairs balance each other, so the bonds are not pushed out of place and the angle stays at 180°.
- I₃⁻ is an ion with an overall charge of −1, so it is not described as polar or non-polar.
How to draw it
- Count the valence electrons: 3 × I 7 + 1 for the ⁻ charge = 22 valence electrons, 11 pairs.
- Put I in the middle and join it to the two outer atoms with single bonds.
- Give each outer atom lone pairs until it has an octet (H needs only two electrons), then put any electrons left over on the central atom.
- Result: two I-I single bonds, with three lone pairs on I, so I has 10 electrons around it (an expanded octet).
- Formal charge = valence electrons − lone pair electrons − number of bonds. Here: I −1.
Class 11, Chapter 4 Chemical Bonding and Molecular Structure.
Lewis structure of I3-: quick answers
How many valence electrons are in I3-?
3 × I 7 + 1 for the ⁻ charge = 22 valence electrons, 11 pairs.
What are the formal charges in the Lewis structure of I3-?
I −1; every other atom is zero. Formal charge = valence electrons - lone pair electrons - number of bonds.
How many lone pairs are in the Lewis structure of I3-?
9 in all, 3 of them on the central I.