Question

Indicate whether each of the following compounds is expected to be diamagnetic or paramagnetic, and give a reason for your answer in each case: (a) \(\mathrm{NbCl}_{5}\), (b) \(\mathrm{CrCl}_{2}\), (c) \(\mathrm{CuCl}\), (d) \(\mathrm{RuO}_{4}\), (e) \(\mathrm{NiCl}_{2}\).

Short answer

(a) NbCl5: Diamagnetic, since the Nb5+ ion has no unpaired electrons. (b) CrCl2: Paramagnetic, as the Cr2+ ion has 4 unpaired electrons in the 3d orbitals. (c) CuCl: Diamagnetic, because the Cu+ ion has no unpaired electrons. (d) RuO4: Diamagnetic, since the Ru8+ ion has no unpaired electrons. (e) NiCl2: Paramagnetic, as the Ni2+ ion has 2 unpaired electrons in the 3d orbitals.

Step-by-step solution

(a) NbCl5

First, we need the electron configuration of Nb (Niobium). The electron configuration of Nb is [Kr]4d^45s^1. In NbCl5, the Nb atom loses 5 electrons from its outer shells to form an Nb5+ ion. The electron configuration of Nb5+ is [Kr]4d^0. Since there are no unpaired electrons, NbCl5 is diamagnetic.

(b) CrCl2

The electron configuration of Cr (Chromium) is [Ar] 3d^54s^1. In CrCl2, the Cr atom loses 2 electrons from its outer shells to form a Cr2+ ion. The electron configuration of Cr2+ is [Ar] 3d^4. Since there are 4 unpaired electrons in the 3d orbitals, CrCl2 is paramagnetic.

(c) CuCl

The electron configuration of Cu (Copper) is [Ar] 3d^104s^1. In CuCl, the Cu atom loses 1 electron from its outer shells to form a Cu+ ion. The electron configuration of Cu+ is [Ar] 3d^10. Since there are no unpaired electrons, CuCl is diamagnetic.

(d) RuO4

The electron configuration of Ru (Ruthenium) is [Kr] 4d^75s^1. In RuO4, the Ru atom loses 8 electrons from its outer shells to form a Ru8+ ion. The electron configuration of Ru8+ is [Kr] 4d^0. Since there are no unpaired electrons, RuO4 is diamagnetic.

(e) NiCl2

The electron configuration of Ni (Nickel) is [Ar] 3d^84s^2. In NiCl2, the Ni atom loses 2 electrons from its outer shells to form an Ni2+ ion. The electron configuration of Ni2+ is [Ar] 3d^8. Since there are 2 unpaired electrons in the 3d orbitals, NiCl2 is paramagnetic. In conclusion: - NbCl5 is diamagnetic - CrCl2 is paramagnetic - CuCl is diamagnetic - RuO4 is diamagnetic - NiCl2 is paramagnetic

Key concepts

Diamagnetic and Paramagnetic

Understanding the magnetic properties of compounds, such as whether they are diamagnetic or paramagnetic, is crucial in the field of chemistry and can have practical applications in material science and electronics. Diamagnetism and paramagnetism are terms that describe how different substances respond to magnetic fields.

Diamagnetic substances are those that tend to become magnetized in a direction opposite to that of the magnetic field applied to it. They are not attracted to magnets and, in fact, slightly repelled. This property is due to the paired electrons in their electron configuration, which effectively cancel out each other's magnetic moment.

On the other hand, paramagnetic substances have unpaired electrons, which make them inherently magnetic. When exposed to an external magnetic field, these unpaired electrons align in the same direction as the magnetic field, causing the material to be attracted to it. The strength of the paramagnetic property depends on the number of unpaired electrons; the more unpaired electrons, the stronger the magnetic attraction.

Electron Configuration

Electron configuration plays a pivotal role in determining the magnetic properties of atoms and compounds. It refers to the distribution of electrons in an atom or molecule's atomic or molecular orbitals. A stable electron configuration is one where electrons are paired up in their orbitals, fulfilling the 'Pauli Exclusion Principle' which states that no two electrons can occupy the same quantum state simultaneously.

For example, the electron configuration of an atom like neon is fully paired, with electrons in the 1s, 2s, and 2p orbitals forming a stable octet. This complete pairing leads to diamagnetism. Transition metals often have more complex electron configurations with partially filled d or f orbitals, which can lead to unpaired electrons and thus paramagnetism. Determining the electron configuration, especially after ionization as in the case of transition metal complexes, is a key step in predicting magnetic behavior.

Unpaired Electrons

Unpaired electrons are the primary cause of paramagnetism in compounds. They are electrons that are alone in an orbital and thus do not have a paired electron with opposite spin to cancel out their magnetic moment. A substance that has one or more unpaired electrons will exhibit magnetic properties because these electrons' spins can be aligned in a magnetic field, causing the substance to be attracted to the field.

Using Hund's rule, it is possible to predict the presence of unpaired electrons in an atom. Hund's rule states that electrons will fill an empty orbital before they pair up. This is why certain configurations like that of chromium and nickel often result in unpaired electrons following ionization, leading to paramagnetism as observed in compounds like CrCl2 and NiCl2. In chemistry, detecting the presence of unpaired electrons can be done using techniques such as electron paramagnetic resonance (EPR) spectroscopy.