Which one has the highest paramagnetism amongst the following ions? (a) \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}\) (b) \(\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\) (c) \(\left[\mathrm{Cu}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\) (d) \(\left[\mathrm{Zn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\)

The connection between unpaired electrons and paramagnetism is fundamental to understanding magnetic properties in chemistry. Atoms, ions, or molecules with one or more unpaired electrons exhibit paramagnetism, a form of magnetism whereby the material is attracted into an externally applied magnetic field. This attraction can be measured and is indicative of the material's magnetic nature.

Each electron has a property known as 'spin', and electrons in an orbital can either be spin-up or spin-down. When an electron is alone in an orbital, not paired with another of opposite spin, it is considered unpaired. The more unpaired electrons an ion has, the stronger its paramagnetic effect will be. For example, the electronic configuration of a metal ion may show several unpaired electrons, indicating a high level of paramagnetism. On the other hand, if the electrons are all paired, the substance is diamagnetic and will be repelled by a magnetic field.

Understanding the electronic configurations of transition metals is key in predicting the behavior and properties of transition metal complexes. Transition metals are defined by their partially filled d-orbitals and the unique ability to donate these d electrons to form bonds.

Transition Metal Ions and Their Electrons

When transition metals form positive ions, they usually lose their outermost s electrons before any from the d orbital. This affects their magnetic properties. For example, a neutral chromium atom has an atomic number of 24, and an electronic arrangement represented as \text{[Ar] 4s\(^2\)3d\(^4\)}. When it forms a \text{Cr\(^{3+}\)} ion, it loses the two 4s electrons and one 3d electron, resulting in the \text{[Ar] 3d\(^3\)} configuration, with three unpaired electrons contributing to paramagnetism.

The Case of Complex Ions

In complex ions, the situation becomes more intricate as the presence of ligands might cause further splitting of d-orbitals, affecting the number of unpaired electrons. This splitting alters the energy levels within the d subshell and can redistribute electrons, thereby modifying the magnetic properties of the ion.

The magnetic properties of coordination compounds are largely determined by the number and arrangement of unpaired electrons in the d-orbitals of the central transition metal ion. Coordination compounds contain a central metal ion surrounded by molecules or anions known as ligands.

Degree of Paramagnetism

The ligands and the geometry of the complex can influence the electronic structure of the metal ion and thus its magnetic properties. For example, if a ligand causes a large splitting in the energy levels of the d-orbitals, it may force unpaired electrons to pair up, thereby reducing paramagnetism. Conversely, a complex with a weak field ligand may exhibit a high paramagnetism due to a large number of unpaired electrons.

When analyzing these compounds, it's important to not only consider the metal's oxidation state and the electronic configuration but also the nature of the ligands and the overall coordination geometry. This comprehensive approach allows for the determination of whether a complex will demonstrate paramagnetic or diamagnetic tendencies, with strong field ligands often leading to diamagnetism and weak field ligands to paramagnetism.

Experimental Measurement

Magnetic susceptibility measurements can experimentally determine if a compound is paramagnetic. A substance with a high number of unpaired electrons will show a significant attraction to the magnetic field, whereas a compound with paired electrons will be weakly repelled.