Final answer:
The longhand notation for the electron configuration of iron is 1s²2s²2p¶3s²3p¶4s²3d¶, and the noble-gas notation is [Ar]4s²3d¶. For iron cations, the electrons are lost first from the 4s orbital, followed by the 3d orbital for higher charges.
Step-by-step explanation:
The question is asking for the electron configuration of iron (Fe) in both its longhand and noble-gas notations. The electron configuration is the distribution of electrons of an atom or molecule in atomic or molecular orbitals.
Longhand Notation
For iron, the longhand electron configuration is 1s²2s²2p¶3s²3p¶4s²3d¶. This notation shows the sequence in which the atomic orbitals are filled with electrons.
Noble-Gas Notation
The noble-gas shorthand notation is a simplified version of the electron configuration, starting from the nearest noble gas with a lower atomic number. Here, [Ar] represents the electron configuration of argon. The noble-gas notation for iron is [Ar]4s²3d¶. In its common oxidation states, iron loses electrons from the 4s sublevel, resulting in iron(II) with a configuration of [Ar]3d¶, and iron(III) with a configuration of [Ar]3dµ.
When iron forms cations, the 4s electrons are removed before the 3d electrons. A +2 charge is common for transition metals, as they typically have two valence electrons. For iron, Fe²⁺ would have the configuration 1s²2s²2p¶3s²3p¶3d¶, having lost two 4s electrons. Also, Fe³⁺ would have the configuration 1s²2s²2p¶3s²3p¶3dµ, having lost two 4s electrons and one from the 3d sublevel.