Question

How many lone pairs are present in ${I_3}^ -$ at the central atom?

Answer 1

Hint: It is known as triiodide. It is composed of three iodine atoms. It is a linear anion. It is formed by the bonding of diiodine with iodide ion.

Complete step by step answer:
${I_3}^ -$ is generally known as the triiodide ion. It is one of the polyhalogen ions and is composed of three iodine atoms. It is formed by combining aqueous solutions of iodide salts and iodine. It is a linear atom. It is formed by the bonding of ${I_2}$ with ${I^ - }$ ion. Triiodide in red in colour in solution. In this molecule, ${I^ - }$ is the donor atom and ${I_2}$ molecule is the acceptor atom. The electrons are accommodated in the empty d – orbital of the iodine. During the combination of Iodine atoms, the central atom gains a negative charge whose value will be 1. The hybridization of triiodide ions is $s{p^3}d$. The geometry of triiodide ions is linear with a bond angle of 180$^\circ$. The structure of ${I_3}^ -$ is:

An iodine atom has 3 lone pairs of electrons. The central atom in ${I_3}^ -$ has three lone pairs of electrons and is making two bonds with adjacent iodines. Hence, it has a negative charge on it. Thus, the total number of lone pairs of electrons in the structure of ${I_3}^ -$ is 9.
Hence, the correct answer is 9.

Note: Remember that the structure of iodine is a linear structure with all the iodines attached to each other by sigma bonds. The hybridization of the central atom is $s{p^3}d$.