How many electrons are in the iron ion of K3[Fe(CN)6]?
A) 3
B) 5
C) 6
D) 7
E) 4
The correct answer and explanation is:
The correct answer is B) 5.
Explanation:
To determine the number of d electrons in the iron ion of the complex K₃[Fe(CN)₆], follow these steps:
- Identify the oxidation state of the metal (Fe): The complex is K₃[Fe(CN)₆], which means it has three K⁺ ions and one [Fe(CN)₆]³⁻ ion. The cyanide ions (CN⁻) are generally considered as ligands with a charge of -1 each. Since there are six CN⁻ ions, their total negative charge is -6. The overall charge of the complex is -3 (due to the 3 K⁺ ions), and thus, the charge on the iron ion (Fe) must balance the charges from the cyanides. Therefore, the iron ion must have a +3 charge, i.e., Fe³⁺.
- Determine the electron configuration of Fe³⁺: Iron (Fe) has an atomic number of 26, so its ground-state electron configuration is [Ar] 3d⁶ 4s². When Fe loses three electrons to form Fe³⁺, the electrons are removed first from the 4s orbital and then from the 3d orbitals. This results in the electron configuration for Fe³⁺ being [Ar] 3d⁵.
- Count the d electrons: In the Fe³⁺ ion, the 3d orbitals contain 5 electrons.
Therefore, the number of d electrons in the iron ion of K₃[Fe(CN)₆] is 5.