The oxidation number of the central atom in a complex is defined by considering the charge it would have if all ligands and shared electron pairs are removed. It is represented by a Roman numeral in parenthesis following the coordination entity’s name, e.g., Cu(I) in [Cu(CN)₄]³⁻.
How is the oxidation number of the central atom determined in a complex, and how is it represented?
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The oxidation number of the central atom in a complex is determined by considering the charges carried by its ligands and the overall charge of the complex. The sum of the oxidation numbers of all ligands and the complex charge must equal the oxidation state of the central metal. For example, in [Fe(CN)₆]³⁻, each cyanide ligand has a charge of -1, and since the complex has a 3- charge, the oxidation number of Fe is +3.
The oxidation number is represented as a Roman numeral in parentheses after the central metal’s name, indicating its charge, such as iron(III) in the example above.