Question

The ${{I}_{3}}^{-}$ ion has:
a.) Five equatorial lone pairs on the central atom and two axial bonding pairs in the trigonal bi-pyramidal arrangement.
b.) Five equatorial lone pairs on the central atom and two axial bonding pairs in the pentagonal bi-pyramidal arrangement.
c.) Three equatorial lone pairs on the central atom and two axial bonding pairs in the trigonal bi-pyramidal arrangement.
d.) Two equatorial lone pairs on the central atom and three axial bonding pairs in the trigonal bi-pyramidal arrangement.

Answer 1

Hint: We can find the number of lone pair and bond pair and also the shape of the molecule using the valence shell electron pair repulsion theory.

Complete step by step answer:
VSEPR theory helps us to predict the geometry of the molecule from the number of electron pairs and lone pairs around the central atom.
If we talk about molecule of iodine “I”
Atomic number of iodine = 53

Number of valence electrons in oxygen which means the electrons present in the last shell of oxygen = 7
The total number of valence electrons in${{I}_{3}}^{-}$ is 22, iodine has 7 valence electrons and 1 extra electron from one negative charge. Now to complete the octet iodine will form 2 covalent bonds. There are 3 lone pairs and 2 bond pairs on the central atom.
First using the above equation we will draw the Lewis dot structure of${{I}_{3}}^{-}$.

Hybridization number can be calculated by adding the number of sigma bond and lone pair, number of sigma bond on central atom is =2 and lone pair on central atom is = 3. Hybridization number will be 5.
Hybridization = $s{{p}^{3}}d$ and geometry will be trigonal bi-pyramidal.
When arranged in trigonal bi-pyramidal geometry it will have 3 equatorial lone pairs on the central atom and 2 axial bonding pairs.
So, the correct answer is “Option C”.

Note: The geometry and shape of a molecule can be the same or different as the geometry of the molecule depends on the arrangement of lone pair and bond Pair while the shape of a molecule excludes the lone pair on the central atom.