Question

Which of the following ions contains minimum number of unpaired electrons? (a) \(\mathrm{Fe}^{2+}\) (b) \(\mathrm{Fe}^{3+}\) (c) \(\mathrm{Co}^{2+}\) (d) \(\mathrm{Co}^{3+}\)

Short answer

Co^2+ ion contains the minimum number of unpaired electrons.

Step-by-step solution

Determine the Electronic Configuration

The atomic numbers of iron (Fe) and cobalt (Co) must be known. Fe has the atomic number 26, and Co has the atomic number 27. For the ions, we'll subtract electrons corresponding to the charge from the atomic number to determine the electronic configurations.

Write Down the Electronic Configuration for each Ion

Write the electronic configurations of Fe and Co and adjust for the loss of electrons due to positive charge:- Fe^2+: [Ar] 3d^6 4s^0- Fe^3+: [Ar] 3d^5 4s^0- Co^2+: [Ar] 3d^7 4s^0- Co^3+: [Ar] 3d^6 4s^0

Identify the Number of Unpaired Electrons

Count the number of unpaired electrons in the 3d subshell for each ion:- Fe^2+: 4 unpaired electrons- Fe^3+: 5 unpaired electrons- Co^2+: 3 unpaired electrons- Co^3+: 4 unpaired electrons

Choose the Ion with the Minimum Number of Unpaired Electrons

After counting the unpaired electrons in the d orbitals of each ion, we can determine that Co^2+ has the minimum number of unpaired electrons.

Key concepts

Electronic Configuration

Understanding the concept of electronic configuration is fundamental to grasp the properties and behaviors of atoms and ions, especially in transition metals. It refers to the arrangement of electrons in an atom’s orbitals, which follow a set of specific rules. Electrons occupy orbitals starting from the lowest energy level, filling up to the highest as per the Aufbau principle. Each orbital can hold a maximum of two electrons with opposite spins, as dictated by the Pauli exclusion principle. Additionally, Hund's rule states that electrons will fill degenerate orbitals (orbitals with the same energy) singly before doubling up.

For transition metals, the electronic configuration becomes slightly more complex due to the addition of electrons to the d orbitals. These metals are characterized by their partially filled d subshells, which can give rise to a variety of oxidation states and the phenomenon of unpaired electrons, critical to magnetic properties and chemical reactivity. When transition metals form ions, electrons are usually removed first from the s orbital, followed by the d orbital; this order is key to determining an ion’s magnetic properties and its number of unpaired electrons.

D-Block Elements

D-block elements, also known as transition metals, are located in the central portion of the periodic table, specifically in groups 3 to 12. These elements are unique in that they have a valence electron configuration that includes the d subshell. Unlike s and p blocks, where the addition of electrons follows a more predictable pattern, the d-block can create a diverse set of electronic configurations and complex behaviors.

In evaluating transition metal ions, one of the most interesting aspects is their ability to form different ions with varying numbers of unpaired electrons. This characteristic has implications in their color, magnetic properties, and catalytic activities, which are prevalent in many industrial and biological processes. The d-block elements often display variable oxidation states and complexation with ligands, further diversifying their chemical properties and uses in coordination chemistry.

Transition Metal Ions

Transition metal ions arise when transition metals lose electrons to form positively charged ions. This process is influenced by the electron configuration and the energetics of electron removal. When electrons are removed, it typically occurs from the outermost s orbital first and then from the d orbitals. As a result, these ions have an incomplete d subshell, which plays a pivotal role in their chemical behavior.

In the context of the exercise, the number of unpaired electrons within these d orbitals becomes paramount. Transition metal ions with fewer unpaired electrons are less magnetic and often form distinctively colored compounds due to the specific electronic transitions that are possible when light interacts with them. For instance, the color of gemstones, the capacity to absorb and reflect particular wavelengths of light, and the magnetic properties of materials are all influenced by the presence of transition metal ions and their electronic configurations. From catalysts in industrial synthesis to biological enzymes, the properties of these ions are harnessed in various applications, and understanding their electron configuration is key to predicting their behavior in chemical reactions.