Question

In $[Co(CN)_6]^{3-}$, how do we know how many lone pairs the Co is getting? It can be 6 or 12, right?

• A. 6 lone pairs
• B. 12 lone pairs
• C. The number of lone pairs depends on the oxidation state of Co.
• D. The number of lone pairs depends on the charge of the complex.

Answer 1

Answer: (A)

The Cobalt ion ($Co^{3+}$) receives 6 lone pairs from the 6 cyanide ligands.

Answer 2

To determine the number of lone pairs the Cobalt (Co) ion receives in the complex $[Co(CN)_6]^{3-}$, we follow these steps:

1. Identify the Central Metal Ion and Ligands:

   • Central Metal Ion: Cobalt (Co)
   • Ligand: Cyanide ($CN^-$)

2. Determine the Oxidation State of the Central Metal Ion:

   • Let the oxidation state of Co be $x$.
   • The charge of the cyanide ligand ($CN^-$) is -1.
   • The overall charge of the complex is -3.
   • The equation is: $x + 6 \times (-1) = -3$
   • $x - 6 = -3$
   • $x = +3$.
   • The central metal ion is $Co^{3+}$.

3. Identify the Donor Atom and Lone Pairs of the Ligand:

   • The cyanide ion ($CN^-$) is a monodentate ligand, forming one bond with the metal.
   • The donor atom in $CN^-$ is the carbon atom.
   • The Lewis structure of $CN^-$ is $[:C \equiv N:]^-$. The carbon atom has one lone pair of electrons available for donation.

4. Calculate the Total Number of Lone Pairs Donated:

   • There are 6 cyanide ligands.
   • Each cyanide ligand donates 1 lone pair from its carbon atom to the $Co^{3+}$ ion.
   • Total lone pairs received by Cobalt = (Number of ligands) $\times$ (Lone pairs donated per ligand)
   • Total lone pairs = $6 \times 1 = 6$.

The Cobalt ion ($Co^{3+}$) receives 6 lone pairs. The number 12 would represent the total number of electrons donated (6 lone pairs $\times$ 2 electrons/lone pair), but the question specifically asks for the number of "lone pairs".