Effective Atomic Number Rule

To understand the rules for effective atomic number we need to understand the following concepts:

Coordination Complexes

Coordination complexes are ions or molecules that are created when ligands are arranged in a specific way around a central metal atom. Usually, these ligands are ions or molecules that have one or more electron pairs that are available for bonding. One of the central metal atoms or ions in a coordination complex serves as the nucleus around which the ligands coordinate. The complex receives electrons from this central metal.

Ligands

To form coordinate bonds, ligands are molecules or ions that give electron pairs to the central metal atom or ion. The central metal atom/ion is surrounded by these ligands, which affect its characteristics.

Electron Counting

Counting the total electrons contributed by the surrounding ligands and the central metal atom/ion is necessary to determine the Effective Atomic Number.

Contributions from Central Metal Atom/Ion

The valence shell of the central metal atom/ion donates electrons to the coordination complex. The amount of electrons contributed depends on the metal’s position in the periodic table and degree of oxidation.

Contributions from Ligands

The coordination complex receives electron pairs from ligands. Each ligand contributes a different number of electrons based on the kind of bond it forms with the central metal atom or ion and its nature.

Method of Calculation

The electrons contributed by the surrounding ligands and the central metal atom/ion are added up to determine the Effective Atomic Number. Mathematically the calculation of effective atomic number is done by Sidgwick formula which is give below:

“Effective Atomic Number,” or “EAN,” is a theoretical concept used to explain electronic structure and stability of coordination compounds. It is the total number of electrons that an atom or ion in a compound appears to have in theory, taking into account both the electrons it actually possesses as valence and the electrons that are donated by nearby ligands.

The concept of Effective Atomic Number (EAN) is essential in chemistry to understand complex coordination compounds and their behaviors. This article explores the concept of effective atomic number, including its application to coordination compounds, the development of the Sidgwick EAN Rule, and real-world examples.