Problem 11 - Chemistry and Chemical Reactivity

Question

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

Step-by-Step Solution

Answer

(a) V\(^{3+}\); (b) Co\(^{3+}\); (c) Cr\(^{2+}\); (d) Sc\(^{+}\).

Step 1: Understand Isoelectronic Species

Isoelectronic species have the same number of electrons. To solve this problem, we need to determine the number of electrons in each given ion and find a transition metal cation from the first series (Sc to Zn) with the same electron count.

Step 2: Determine Electron Configuration of the Given Ions

First, find the atomic number of the element to determine the neutral atom's electron configuration. Then, adjust for the charge by adding or subtracting electrons. For example, neutral Fe has 26 electrons, so Fe\(^{3+}\) has 23 electrons.

Step 3: Find Isoelectronic Cation for Fe^{3+}

Fe\(^{3+}\) has 23 electrons. The atomic number of V (Vanadium) is 23, which means the cation V\(^{3+}\) also has 23 electrons. Therefore, V\(^{3+}\) is isoelectronic with Fe\(^{3+}\).

Step 4: Find Isoelectronic Cation for Zn^{2+}

Zn\(^{2+}\) has lost 2 electrons from neutral Zn (with 30 electrons), leaving it with 28 electrons. Ni (Nickel) has 28 electrons when neutral, so Ni\(^{2+}\) with 26 electrons cannot match. Use Co\(^{3+}\) with 27 electrons as Zn\(^{2+}\) has no direct match.

Step 5: Find Isoelectronic Cation for Fe^{2+}

After removing 2 electrons from neutral Fe with 26 electrons, Fe\(^{2+}\) has 24 electrons. Therefore, Cr\(^{2+}\), after losing 2 electrons from neutral Cr with 24, also has 24 electrons making Cr\(^{2+}\) isoelectronic with Fe\(^{2+}\).

Step 6: Find Isoelectronic Cation for Cr^{3+}

Cr\(^{3+}\) has 21 electrons (24 from neutral Cr - 3 electrons), matching with Sc\(^+\), which after losing 1 electron from neutral Sc (21 electrons), also has 21 electrons.

Key Concepts

Transition Metals

Transition metals are elements found in the d-block of the periodic table. They are known for their ability to form various oxidation states and colorful compounds. This versatility stems from their unique electron configurations, as transition metals have partially filled d-orbitals. This allows them to easily lose or gain electrons, forming cations with different charges.
Transition metals often have high melting and boiling points. They also typically exist as metals that are lustrous, conductive, and strong. Common examples include iron (Fe), copper (Cu), and zinc (Zn). These elements play critical roles in various industrial applications and biological processes.
To truly understand isoelectronic relationships in transition metals, it’s important to grasp how their electron configuration allows them to form different cations.

Electron Configuration

The electron configuration of an atom describes how electrons are distributed among its atomic orbitals. For transition metals, which have d-block elements, electron configurations play a crucial role in determining their chemical behavior.
For example, the electron configuration of a neutral iron (Fe) atom is \(1s^22s^22p^63s^23p^64s^23d^6\). When forming a cation like \(Fe^{3+}\), three electrons are removed. This results in a new electron configuration of \(1s^22s^22p^63s^23p^63d^5\).
An important concept to understand here is that transition metals lose their outer s-electrons first before losing d-electrons. This characteristic allows for various oxidation states and results in different ionic forms being isoelectronic with one another.

Cations

Cations are positively charged ions formed when an atom loses one or more electrons. Transition metals readily form cations due to their electronic structure.
When a neutral atom transforms into a cation, it loses electrons to achieve a more stable electron configuration. For instance, zinc (Zn), with an electron configuration of \(1s^22s^22p^63s^23p^64s^23d^{10}\), loses two electrons to form \(Zn^{2+}\).
In this case, the electrons are typically removed from the outermost s-orbital, followed by the d-orbitals if needed. It's crucial to note that the goal of this loss is often to achieve an electron configuration similar to that of noble gases, which are known for their stability.

First Series Transition Metals

The first series transition metals range from scandium (Sc) to zinc (Zn) on the periodic table. These elements are unique due to their filling of 3d orbitals while maintaining electrons in their 4s orbitals.
This series includes:

• Scandium (Sc)
• Titanium (Ti)
• Vanadium (V)
• Chromium (Cr)
• Manganese (Mn)
• Iron (Fe)
• Cobalt (Co)
• Nickel (Ni)
• Copper (Cu)
• Zinc (Zn)

These elements are highly valued due to their physical properties and ability to form various alloys. Importantly, understanding their electron configurations and how they form cations is key to determining isoelectronic species as seen in this exercise.