What is the electron configuration for the neutral atom of Iron (Fe)?

The electron configuration for a neutral atom of iron (Fe) is accurately represented as [Ar] 4s² 3d⁶. This configuration can be understood by considering the atomic number of iron, which is 26. This means that an uncharged (neutral) iron atom has 26 electrons.

To determine the electron configuration, electrons are filled into atomic orbitals according to the Aufbau principle, which states that electrons occupy the lowest energy orbitals first. The order of filling typically follows the sequence of increasing energy levels. The argon (Ar) core configuration provides the first 18 electrons, covering the 1s, 2s, 2p, 3s, and 3p orbitals.

After accounting for the argon core, there are 8 electrons left to place. The 4s orbital is filled before the 3d orbital due to its lower energy level. Thus, the next two electrons go into the 4s orbital, giving 4s². This leaves 6 electrons remaining, which are then placed in the 3d orbital, resulting in 3d⁶. Therefore, the complete configuration of iron is expressed as [Ar] 4s² 3