Effective Atomic Number of Ni(CO)4
Ni(CO)4 is a coordination complex consisting of a nickel atom surrounded by four carbon monoxide ligands. To determine the effective atomic number of Ni(CO)4, we need to consider the contribution of both the metal atom and the ligands.

Nickel Atom
- Nickel in its neutral state has an atomic number of 28.
- In Ni(CO)4, the nickel atom undergoes a coordination bond with four carbon monoxide ligands, resulting in a coordination number of 4.

Carbon Monoxide Ligands
- Each carbon monoxide ligand contributes one electron from the lone pair on the carbon atom to the coordination bond.
- The oxygen atom in carbon monoxide also contributes one electron, resulting in a total of two electrons from each ligand.

Calculation of Effective Atomic Number
- Since each carbon monoxide ligand contributes two electrons, the total electron count from the ligands is 4 ligands x 2 electrons/ligand = 8 electrons.
- The effective atomic number of Ni(CO)4 can be calculated as the sum of the atomic number of the metal atom and the total number of electrons contributed by the ligands.
- Therefore, the effective atomic number of Ni(CO)4 = 28 (atomic number of Ni) + 8 (electrons from ligands) = 36.
In conclusion, the effective atomic number of Ni(CO)4 is 36, taking into account the contribution of both the nickel atom and the carbon monoxide ligands in the coordination complex.