Problem 3 - Chemistry and Chemical Reactivity

Question

Identify a cation of a first series transition metal that is isoelectronic with each of the following. (a) \(\mathrm{Fe}^{3+}\) (b) \(\mathrm{Zn}^{2+}\) (c) \(\mathrm{Fe}^{2+}\) (d) \(\mathrm{Cr}^{3+}\)

Step-by-Step Solution

Answer

(a) Mn²⁺, (b) none, (c) Co³⁺, (d) V²⁺.

Step 1: Determine the Electron Configuration of Each Cation

Begin by determining the electron configuration for each given cation. - For \( \mathrm{Fe^{3+}} \), Iron (Fe) normally has an electron configuration of \( [\mathrm{Ar}] 3d^6 4s^2 \). Upon losing 3 electrons, it becomes \( [\mathrm{Ar}] 3d^5 \).- For \( \mathrm{Zn^{2+}} \), Zinc (Zn) normally has \( [\mathrm{Ar}] 3d^{10} 4s^2 \), but losing 2 electrons results in \( [\mathrm{Ar}] 3d^{10} \).- For \( \mathrm{Fe^{2+}} \), Fe loses 2 electrons from the 4s subshell, resulting in \( [\mathrm{Ar}] 3d^6 \).- For \( \mathrm{Cr^{3+}} \), Chromium's normal configuration is \( [\mathrm{Ar}] 3d^5 4s^1 \). It loses one electron from each of 4s and 3d, becoming \( [\mathrm{Ar}] 3d^3 \).

Step 2: Identify Isoelectronic Cations from the First Transition Series

Find transition metal cations with the same electron configurations as the identified cations:- To match \( \mathrm{Fe^{3+}} \)'s \( [\mathrm{Ar}] 3d^5 \), \( \mathrm{Mn^{2+}} \) is isoelectronic.- To match \( \mathrm{Zn^{2+}} \)'s \( [\mathrm{Ar}] 3d^{10} \), no other transition metal cation is isoelectronic when considering oxidation states typically encountered.- To match \( \mathrm{Fe^{2+}} \)'s \( [\mathrm{Ar}] 3d^6 \), \( \mathrm{Co^{3+}} \) is isoelectronic.- To match \( \mathrm{Cr^{3+}} \)'s \( [\mathrm{Ar}] 3d^3 \), \( \mathrm{V^{2+}} \) is isoelectronic.

Step 3: Compile the Answers

List the transition metal cations that are isoelectronic with each of the provided cations:- (a) \( \mathrm{Fe^{3+}} \) is isoelectronic with \( \mathrm{Mn^{2+}} \).- (b) \( \mathrm{Zn^{2+}} \) does not have a common first-series transition metal cation that is isoelectronic.- (c) \( \mathrm{Fe^{2+}} \) is isoelectronic with \( \mathrm{Co^{3+}} \).- (d) \( \mathrm{Cr^{3+}} \) is isoelectronic with \( \mathrm{V^{2+}} \).

Key Concepts

Isoelectronic Species

Isoelectronic species are atoms, ions, or molecules that have the same number of electrons. Having an identical electron configuration is what makes them isoelectronic. This is interesting because isoelectronic species often exhibit similar chemical properties. In transition metals, identifying isoelectronic species requires examining their electron configurations.

• Isoelectronic does not mean the species have the same charge or belong to the same element. Instead, they have matching electronic structures.
• For example, both \( \mathrm{Fe}^{3+} \) and \( \mathrm{Mn}^{2+} \) share the configuration \( [\mathrm{Ar}] 3d^5 \,\) making them isoelectronic.

Understanding this concept helps in predicting reactions and stability in chemistry.

Transition Metals

Transition metals are elements that have partially filled d subshells. This gives them unique properties such as complex ion formation, variable oxidation states, and distinctive colors. They are found in the center of the periodic table and include well-known elements like iron, copper, and zinc.

• The ability to lose different numbers of d electrons allows transition metals to form cations with different charges.
• Transition metals like \( \mathrm{Fe}, \mathrm{Co}, \) and \( \mathrm{Ni} \) are part of the first transition series.

These elements play a crucial role in various chemical processes and industrial applications.

Cation Identification

Identifying cations, especially in transition metals, requires understanding of their electron loss. Transition metal cations are formed by losing electrons, often from the 4s and 3d orbitals.

• The charge of a cation depends on how many electrons are lost. For example, \( \mathrm{Fe^{2+}} \) means iron loses two electrons.
• In transition metals, electron removal typically starts from the 4s orbital even though it is filled after 3d.

This can lead to multiple cations from the same element, demonstrating the variable oxidation states of transition metals.

First Transition Series

The first transition series includes elements from scandium (Sc) to zinc (Zn). These elements are in the fourth period of the periodic table and are known for their d-block characteristics.

• These elements have partially filled d orbitals, which are key to their chemical behavior.
• Example elements include \( \mathrm{Cr}, \mathrm{Mn}, \) and \( \mathrm{Fe} \), each forming cations with diverse properties.

Their versatile oxidation states make them critical components in both industrial contexts and biological systems, with many acting as essential enzymatic cofactors.