Question

The effective atomic number of Ni in $\left[Ni(NH_3)_3(en)(H_2O)\right]^{+2}$ will be _______ (Atomic number of Ni = 28)

Answer 1

38

Answer 2

The effective atomic number (EAN) of a central metal atom in a complex is calculated using the formula:

$\text{EAN} = \text{Atomic number (Z)} - \text{Oxidation state} + 2 \times \text{Coordination number}$

For the complex $\left[Ni(NH_3)_3(en)(H_2O)\right]^{+2}$:

1. Identify the central metal atom and its atomic number:
   The central metal atom is Nickel (Ni).
   Atomic number of Ni (Z) = 28 (given).

2. Determine the oxidation state of Ni:
   Let the oxidation state of Ni be $x$.
   $NH_3$ (ammonia) is a neutral ligand, so its charge is 0.
   $en$ (ethylenediamine, $H_2N-CH_2-CH_2-NH_2$) is a neutral ligand, so its charge is 0.
   $H_2O$ (water) is a neutral ligand, so its charge is 0.
   The overall charge of the complex is +2.
   So, $x + 3(0) + 1(0) + 1(0) = +2$
   $x = +2$
   The oxidation state of Ni is +2.

3. Determine the coordination number:
   The coordination number is the total number of donor atoms directly bonded to the central metal ion.

   • $NH_3$ is a monodentate ligand (1 donor atom), and there are 3 such ligands. Contribution = $3 \times 1 = 3$.
   • $en$ (ethylenediamine) is a bidentate ligand (2 donor atoms), and there is 1 such ligand. Contribution = $1 \times 2 = 2$.
   • $H_2O$ is a monodentate ligand (1 donor atom), and there is 1 such ligand. Contribution = $1 \times 1 = 1$.
     Total coordination number = $3 + 2 + 1 = 6$.

4. Calculate the EAN:
   Using the EAN formula:
   $\text{EAN} = 28 - (+2) + 2 \times 6$
   $\text{EAN} = 28 - 2 + 12$
   $\text{EAN} = 26 + 12$
   $\text{EAN} = 38$

The effective atomic number of Ni in the given complex is 38.