Question

What is the effective atomic number? Calculate the effective atomic number of Copper\[Z\] in \[\,\,{\left[ {Cu{{(N{H_3})}_4}} \right]^{2 + }}\]

Answer 1

Hint: To calculate the effective atomic number we must have to calculate the oxidation number of metal ion in the given complex and which type of ligands are bonded with the metal ion.

Complete step by step answer:
Effective atomic number-it is the total number of electrons of metal ion in the complex which is bonded with the ligands. As in case of copper metal in \[\,\,{\left[ {Cu{{(N{H_3})}_4}} \right]^{2 + }}\] complex, the total number of electrons can be calculated by the calculation of oxidation state of copper metal which tells us that how many electrons are lost from the metal atom in the complex and the donation of electrons from four ammonia ligands.
Calculation of oxidation state of copper metal- suppose \[y\] is the oxidation state of copper, in this complex ammonia ligand is a neutral ligand so its formal charge is zero. Hence the oxidation number of Copper is \[ + 2\].
\[\begin{array}{c}
{\left[ {Cu{{(N{H_3})}_4}} \right]^{2 + }} = + 2\\
y\,+\,(4 \times 0) = + 2\\
y = + 2
\end{array}\]
The number of electrons of \[Cu = 29\]
The number of electrons in \[C{u^{ + 2}} = 27\]
The eight electrons come from the ammonia ligands which are directly attached with copper and contribute 2 electrons each and 27 electrons from atomic number of Copper after losing two electrons.
The number of electrons from one ammonia ligand \[ = 2\]
The total number of electrons from ammonia ligands(monodentate) \[ = 2x4 = 8\]
Now the total number of electrons in \[\,\,{\left[ {Cu{{(N{H_3})}_4}} \right]^{2 + }} = 27 + 8 = 35\]
Therefore, the total effective atomic number of Copper is 35.

Note:
As we know from the above discussion, an effective atomic number of Copper gives the average atomic number of copper metal ion which is the number of protons of copper atom in the complex. More is the number of ligands, greater will be the donation of electrons to the metal ion which increases the effective atomic number in the complex.