Problem 30 - Chemistry in 30 days

Question

Which one of the following shows maximum paramagnetic character? (a) \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6} \mathrm{l}^{3+}\right.\) (b) \(\left[\mathrm{Fe}(\mathrm{CN})_{6} \mathrm{l}^{4+}\right.\) (c) \(\mid \mathrm{Fe}(\mathrm{CN})_{6} l^{3+}\) (d) \(\left[\mathrm{Cu}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\)

Step-by-Step Solution

Answer

(a) \\( [\mathrm{Cr}(\mathrm{H}_2\mathrm{O})_6]^{3+}\\) shows maximum paramagnetic character.

Step 1: Identify Electron Configuration

We need to determine the electron configurations for the central metal ions of each complex. Paramagnetic substances have unpaired electrons, so we will identify the presence and number of these unpaired electrons. (a) For \([\mathrm{Cr}(\mathrm{H}_2\mathrm{O})_6]^{3+}\), chromium (Cr) has an electronic configuration: [Ar] 3d\(^5\) 4s\(^1\). As a 3+ ion, its configuration is: [Ar] 3d\(^3\) with 3 unpaired electrons. (b) For \([\mathrm{Fe}(\mathrm{CN})_6]^{4-}\), iron (Fe) typically has an electronic configuration: [Ar] 3d\(^{6}\) 4s\(^{2}\). As Fe\(^2+\), it has [Ar] 3d\(^6\). CN\(^-\) is a strong field ligand, causing pairing of the electrons, resulting in 0 unpaired electrons. (c) For \([\mathrm{Fe}(\mathrm{CN})_6]^{3-}\), in a similar vein, iron becomes Fe\(^{3+}\) with an electron configuration of [Ar] 3d\(^{5}\), but CN\(^-\) still causes pairing, resulting in only 1 unpaired electron. (d) For \([\mathrm{Cu}(\mathrm{H}_2\mathrm{O})_6]^{2+}\), copper (Cu) ionically [Ar] 3d\(^{10}\) 4s\(^{1}\). As Cu\(^{2+}\), it has [Ar] 3d\(^9\) with 1 unpaired electron.

Step 2: Determine Maximum Paramagnetism

The paramagnetic character depends on the number of unpaired electrons. More unpaired electrons mean more paramagnetic character. Based on the electron configurations:- \([\mathrm{Cr}(\mathrm{H}_2\mathrm{O})_6]^{3+}\) has 3 unpaired electrons. - \([\mathrm{Fe}(\mathrm{CN})_6]^{4-}\) has 0 unpaired electrons. - \([\mathrm{Fe}(\mathrm{CN})_6]^{3-}\) has 1 unpaired electron.- \([\mathrm{Cu}(\mathrm{H}_2\mathrm{O})_6]^{2+}\) has 1 unpaired electron. Therefore, \([\mathrm{Cr}(\mathrm{H}_2\mathrm{O})_6]^{3+}\) exhibits the maximum paramagnetic character with 3 unpaired electrons.

Key Concepts

Electron Configuration

Electron configuration is a fundamental concept that helps us understand how electrons are arranged around the nucleus of an atom. It's like a blueprint that shows each electron's location within atomic orbitals. The electrons fill these orbitals according to specific rules, primarily Hund's Rule and the Pauli Exclusion Principle. Students often learn that electrons fill lower energy levels first, following the atomic orbitals order: 1s, 2s, 2p, 3s, 3p, and so on.

In transition metals, the 3d subshell is particularly important. The distribution of electrons results in unique properties, especially in their ionic forms. For instance, in the exercise, we observed how converting chromium to a Cr extsuperscript{3+} ion altered its configuration to [Ar] 3d extsuperscript{3}, having significant implications on magnetism and chemical behavior. By understanding electron configurations, students gain insight into the underlying structure that dictates an element's chemical properties.

Unpaired Electrons

Unpaired electrons play a crucial role in determining a substance's magnetic properties. When electrons occupy orbitals within an atom or ion, they seek to minimize and remain in separate orbitals as much as possible, called 'unpaired state'. When electrons are unpaired, they contribute to magnetic fields in materials, creating what is known as paramagnetism. The more unpaired electrons present, the stronger the paramagnetic effects observed.

In the given exercise, we identified the number of unpaired electrons in various transition metal complexes. For instance,

• Cr(H extsubscript{2}O) extsubscript{6} extsuperscript{3+} has three unpaired electrons,
• Fe(CN) extsubscript{6} extsuperscript{4−} has none.

The disparity in unpaired electrons highlights why certain complexes exhibit more substantial paramagnetic character than others. As students explore this, they comprehend how magnetic properties are tied to electron arrangements.

Transition Metal Complexes

Transition metal complexes represent a fascinating and vital area within chemistry, connecting the behavior of transition metals with other chemical components known as ligands. These complexes form when ligands donate electron pairs to a central transition metal ion, creating unique compounds.

The properties and behavior of transition metal complexes are significantly influenced by factors like the nature of ligands, the oxidation state of the metal, and the electron configuration. For example, in the assessment,

• Cr(H extsubscript{2}O) extsubscript{6} extsuperscript{3+} includes a weaker field ligand, water, which influences unpaired electron count.
• Fe(CN) extsubscript{6} complexes involve strong field ligands, cyanide (CN extsuperscript{-}), known for causing electron pairing in d-orbitals.

Understanding these interactions allows a deeper look at how transition metal complexes exhibit different chemical and physical properties, such as color, reactivity, and magnetism. For students, studying these complexes offers insight into advanced chemical concepts and the reasons behind the unique attributes of transition metals.