Question

Comment on the observation that \(\mathrm{K}_{3}\left[\mathrm{Cr}_{2} \mathrm{Cl}_{9}\right]\) is strongly paramagnetic but \(\mathrm{K}_{3}\left[\mathrm{W}_{2} \mathrm{Cl}_{9}\right]\) is diamagnetic.

Short answer

The difference in magnetism is due to Cr's unpaired electrons leading to paramagnetism, while W forms metal-metal bonds, causing diamagnetism.

Step-by-step solution

Identify the Central Metal Atoms

In the compounds \(\mathrm{K}_{3}[\mathrm{Cr}_{2}\mathrm{Cl}_{9}]\) and \(\mathrm{K}_{3}[\mathrm{W}_{2} \mathrm{Cl}_{9}]\), the central metal atoms are chromium (Cr) and tungsten (W) respectively.

Determine the Oxidation States

For both compounds, the metal is part of a mixed halide metal cluster, typically having an oxidation state of +3 due to the charge balance with chlorine ions and the potassium counter ions.

Electron Configuration of Metal Atoms

Chromium in the +3 oxidation state has the electronic configuration \([\mathrm{Ar}] 3d^3\), indicating 3 unpaired electrons. Tungsten in the +3 oxidation state will have the configuration \([\mathrm{Xe}] 4f^{14} 5d^3 6s^0\), but due to involvement in bonding, it can end up with paired electrons.

Assess the Magnetic Properties

Cr has 3 unpaired 3d electrons leading to paramagnetism. In \([\mathrm{W}_{2} \mathrm{Cl}_{9}]^{3-}\), W will partake in metal-metal bonding which can lead to electron pairing, resulting in diamagnetic properties.

Key concepts

Paramagnetism

Paramagnetism is a type of magnetism that occurs in materials which have unpaired electrons. When exposed to an external magnetic field, these unpaired electrons align with the field, making the material attracted to the magnet. This property is commonly observed in transition metals, which have partially filled d orbitals, resulting in unpaired electrons.

In the case of the compound \(\mathrm{K}_{3}[\mathrm{Cr}_{2}\mathrm{Cl}_{9}]\), the Chromium (Cr) ions are in a +3 oxidation state. This gives each Cr ion a 3d electron configuration that includes 3 unpaired electrons. These unpaired electrons make the compound strongly paramagnetic. The electrons align themselves in response to an external magnetic field and enhance the magnetic effect.

Paramagnetism is what you'd expect when there are unpaired electrons present, especially in transition metal complexes where d electrons are common.

Diamagnetism

Diamagnetism arises in materials where all electrons are paired. In such materials, an external magnetic field induces tiny magnetic fields within the atoms that oppose the applied field, causing a very weak repulsion.

For the compound \(\mathrm{K}_{3}[\mathrm{W}_{2}\mathrm{Cl}_{9}]\), tungsten (W) is in a +3 oxidation state, similar to chromium in \(\mathrm{K}_{3}[\mathrm{Cr}_{2}\mathrm{Cl}_{9}]\). However, in this compound, tungsten's electron involvement in metal-metal bonding results in paired electrons.

This electron pairing leads to the compound's diamagnetic nature. There's no unpaired electron left to contribute to magnetic properties, and the result is a weak repulsion from magnetic fields. The ability of tungsten to form bonds with a wide range of electron interactions allows these pairings, differentiating it from chromium's behavior in similar compounds.

Transition Metal Chemistry

Transition metals are elements found in the d-block of the periodic table. They are unique due to their partially filled d orbitals. These unfilled d orbitals give rise to unique properties including variable oxidation states, the creation of colored compounds, and complex magnetic behaviors.

The magnetic properties in transition metal chemistry are directly linked to the configuration of their d electrons. In the discussed compounds, transition metals such as chromium and tungsten exhibit varied magnetic characteristics because of their nature to form different electron arrangements.

Transition metals like Cr and W exhibit various properties due to their d orbital's complex interactions. These include:

• Diverse oxidation states
• Formation of various complex ions and compounds
• Interesting magnetic and optical properties

Understanding these characteristics allows us to predict the behavior of compounds like \(\mathrm{K}_{3}[\mathrm{Cr}_{2}\mathrm{Cl}_{9}]\) and \(\mathrm{K}_{3}[\mathrm{W}_{2}\mathrm{Cl}_{9}]\) in magnetic fields.

Electron Configuration

Electron configuration determines the arrangement of electrons in an atom's orbitals and is a fundamental factor in explaining the chemical and physical properties of the element or compound.

In \(\mathrm{K}_{3}[\mathrm{Cr}_{2}\mathrm{Cl}_{9}]\), the Cr ions in a +3 oxidation state have the electronic configuration \([\mathrm{Ar}] 3d^3\), resulting in 3 unpaired electrons that account for the compound's paramagnetic property.

On the other hand, in \(\mathrm{K}_{3}[\mathrm{W}_{2}\mathrm{Cl}_{9}]\), W ions typically start with a configuration of \([\mathrm{Xe}] 4f^{14} 5d^3 6s^0\). However, the formation of \(\mathrm{W}_{2}\) bonds can cause available unpaired electrons to pair up, leading to a diamagnetic property.

Transition metals often change their electron configuration through oxidation or during compound formation, significantly affecting their magnetic behavior.

Oxidation States

Oxidation states refer to the degree of oxidation of an atom in a compound. The oxidation state is an indicator of an atom's electron activity, such as gaining or losing electrons during chemical reactions. It's crucial for predicting the properties and reactivity of compounds.

In the compounds \(\mathrm{K}_{3}[\mathrm{Cr}_{2}\mathrm{Cl}_{9}]\) and \(\mathrm{K}_{3}[\mathrm{W}_{2}\mathrm{Cl}_{9}]\), both chromium and tungsten exhibit a +3 oxidation state. This common oxidation state typically indicates a certain predictability in their behavior; however, their magnetic properties vary significantly due to differences in electron configuration and bonding.

Transition metals can exhibit a variety of oxidation states which makes them versatile for a wide range of reactions and compounds. This versatility can be illustrated as:

• Diverse chemical reactivity
• Able to form different compounds with varied properties
• Ability to show unique magnetic attributes

Understanding oxidation states helps in explaining why similar oxidation states in chromium and tungsten lead to different magnetic properties in their compounds.