Problem 50 - Chemistry The Science in Context

Question

Dietary Supplement Chromium picolinate is an over-thecounter dict aid sold in many pharmacics. The \(\mathrm{Cr}^{3+}\) ions in this coordination compound are in an octahedral field. Is the compound paramagnetic or diamagnetic?

Step-by-Step Solution

Answer

Answer: Chromium picolinate (Cr³⁺) is a paramagnetic compound.

Step 1: Identify the element and its electron configuration

Chromium has an atomic number of 24. The ground state electron configuration of Chromium is [Ar] \(3d^5 4s^1\). Now, we need to determine the electron configuration of the \(\mathrm{Cr}^{3+}\) ion.

Step 2: Determine the electron configuration of the ion

To obtain the electron configuration of the \(\mathrm{Cr}^{3+}\) ion, we need to remove 3 electrons from the ground state electron configuration of Chromium. Electrons are removed from the outermost shell first, which in this case means removing 1 electron from the 4s orbital and 2 electrons from the 3d orbitals. Therefore, the electron configuration of the \(\mathrm{Cr}^{3+}\) ion is [Ar] \(3d^3\).

Step 3: Check for unpaired electrons

The 3d orbitals can hold a maximum of 10 electrons. Since the \(\mathrm{Cr}^{3+}\) ion has 3 electrons in its 3d orbitals, there must be at least one unpaired electron. This is because the first two electrons will pair up in the lower energy orbitals and the third electron will remain unpaired.

Step 4: Determine if the compound is paramagnetic or diamagnetic

As we have found an unpaired electron in the electron configuration of the \(\mathrm{Cr}^{3+}\) ion, the compound Chromium picolinate is paramagnetic. Paramagnetic compounds have unpaired electrons, whereas diamagnetic compounds have no unpaired electrons.

Key Concepts

Chromium Ions

When we talk about chromium ions, especially in coordination chemistry, it mostly revolves around the chromium in a charged state. Chromium often forms ions like \(\text{Cr}^{3+}\), which is common in many compounds, such as dietary supplements. In these compounds, chromium ions are surrounded by ligands, creating a complex structure.

In the case of \(\text{Cr}^{3+}\), the chromium atom loses three electrons. This ionization is crucial as it defines the electron configuration and, ultimately, the chemical properties of the compound. Understanding chromium ions helps in predicting the behavior of the compounds they form, such as how they interact with other molecules.

Electron Configuration

Electron configuration is a way of distributing electrons in an atom or ion. For chromium, the ground state electron configuration is \([\text{Ar}] \ 3d^5 \ 4s^1\).

When chromium becomes \(\text{Cr}^{3+}\), it loses three electrons. We remove one from the 4s orbital and two from the 3d orbitals. This loss gives \([\text{Ar}] \ 3d^3\) as the electron configuration for \(\text{Cr}^{3+}\).

In electron configuration:

• The order of filling starts from lower to higher energy levels.
• Electrons are removed from the highest energy level first during ionization.

This adjusted configuration is essential for determining the magnetic properties of a compound.

Paramagnetism and Diamagnetism

Paramagnetism and diamagnetism are properties referring to how a substance responds to a magnetic field. It all depends on the presence of unpaired electrons.

Paramagnetic:

• Materials have one or more unpaired electrons.
• They are attracted to magnetic fields.
• \(\text{Cr}^{3+}\) is paramagnetic due to its unpaired electron.

Diamagnetic:

• Materials have all paired electrons.
• They are not attracted to magnetic fields.

Determining if \(\text{Cr}^{3+}\) is paramagnetic involves checking its electron configuration for unpaired electrons. Since \([\text{Ar}] \ 3d^3\) has unpaired electrons, chromium picolinate is paramagnetic. Understanding these magnetic properties helps in various applications, including material synthesis and magnetic resonance imaging (MRI).