Numford
Hybridisation

Hybridisation of I₃⁻

The central I atom is sp³d hybridised (hybridization by the VSEPR count): 2 sigma bonds and 3 lone pairs give a linear shape, bond angle 180°.

III
  • I
  • lone pair

I₃⁻Triiodide ion

Linear

AB₂E₃: 2 bond pairs, 3 lone pairs on central I

  • Hybridisationsp³d
  • Bond angle180°
  • Polarityion, charge −1

Why this shape

  1. 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.
  2. Steric number = two sigma bonds + three lone pairs = 5, so the central I is sp³d hybridised.
  3. 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.
  4. All three lone pairs take the equatorial positions, 120 degrees apart, and the two bonds point up and down.
  5. The lone pairs balance each other, so the bonds are not pushed out of place and the angle stays at 180°.
  6. I₃⁻ is an ion with an overall charge of −1, so it is not described as polar or non-polar.

Lewis structure

22 valence electrons
III−

Formal charges: I −1

Working

Why this hybridisation and shape

  1. 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.
  2. Steric number = two sigma bonds + three lone pairs = 5, so the central I is sp³d hybridised.
  3. 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.
  4. All three lone pairs take the equatorial positions, 120 degrees apart, and the two bonds point up and down.
  5. The lone pairs balance each other, so the bonds are not pushed out of place and the angle stays at 180°.
  6. I₃⁻ is an ion with an overall charge of −1, so it is not described as polar or non-polar.

Class 11, Chapter 4 Chemical Bonding and Molecular Structure.

Questions

Hybridisation of I3-: quick answers

What is the hybridisation of I3-?

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.

What is the shape of I3- and its bond angle?

Linear, with a bond angle of 180 degrees. 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°.

How many lone pairs are on the central atom of I3-?

3 lone pairs. 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.

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