Problem 78 - Chemistry The Central Science In Si Units

Question

How would we describe a substance that contains only paired electrons and is weakly repelled by a magnetic field? Which of the following ions would you expect to possess similar characteristics: \(\mathrm{H}_{2}^{-}, \mathrm{Ne}_{2}^{+}, \mathrm{F}_{2}, \mathrm{O}_{2}^{2+}\) ?

Step-by-Step Solution

Answer

 ext{F}_{2} is diamagnetic and contains only paired electrons.

Step 1: Define the Phenomenon

We are looking for a substance that contains only paired electrons, which means it is diamagnetic. A diamagnetic substance is weakly repelled by a magnetic field because it does not have unpaired electrons.

Step 2: Identify Electron Configuration

Assess the electron configuration of the given ions to determine their magnetic properties. Specifically, look for unpaired electrons. An atom or ion is diamagnetic if all electrons are paired, while it is paramagnetic if at least one electron is unpaired.

Step 3: Evaluate Each Ion

- **
0 ext{H}_{2}^{-}**: This ion may have unpaired electrons based on its electron configuration; hence possibly paramagnetic. - ** ext{Ne}_{2}^{+}**: Neutrals like neon are normally fully paired, but the loss of an electron (+) might create unpaired electrons. - ** ext{F}_{2}**: F2, being a molecule of homonuclear diatomic fluorine, has all electrons paired in molecular orbitals, thus diamagnetic. - ** ext{O}_{2}^{2+}**: Removing two electrons from O2 potentially leaves it with unpaired electrons, thus it is likely paramagnetic.

Step 4: Confirm Characteristics

Upon analysis,  ext{F}_{2} is the only species with all electrons paired, corresponding to diamagnetic behavior. The others have scenarios where unpaired electrons may exist due to bonding or charge alteration, leading to paramagnetism.

Key Concepts

Electron Configuration

Electron configuration refers to the arrangement of electrons in the orbitals of an atom or molecule. Understanding this configuration is essential in determining a substance's chemical and magnetic properties. Electrons occupy orbitals following a specific order based on increasing energy levels: first filling lower energy orbitals, then higher ones.
This is dictated by quantum mechanics and follows principles such as the Aufbau principle, Pauli exclusion principle, and Hund's rule.

• Aufbau Principle: Electrons fill from lower to higher energy orbitals, such as from 1s to 2s, 2p, and so on.
• Pauli Exclusion Principle: No two electrons will have identical quantum numbers, meaning an orbital can hold a maximum of two electrons with opposite spins.
• Hund's Rule: Electrons will fill degenerate orbitals (orbitals with the same energy level) singly before pairing up.

By examining the electron configurations of ions or molecules, we can determine whether electrons are paired or unpaired. This reveals whether the substance is diamagnetic or paramagnetic, two key magnetic properties.

Paramagnetism

Paramagnetism is a form of magnetism that arises when unpaired electrons are present in a material. Unlike diamagnetics, which have electrons entirely in pairs, paramagnetic substances have at least one unpaired electron. These unpaired electrons are freely moving and spin in response to an external magnetic field.
This generates a temporary magnetic field that aligns with the applied magnetic field, causing a weak attraction. However, this magnetic effect vanishes once the external field is removed. By assessing the electron configuration, one can identify paramagnetic materials. If any unpaired electrons are found in the outer shells, the substance exhibits paramagnetic behavior.

• Key Characteristics of Paramagnetism:
  • Presence of one or more unpaired electrons.
  • Weakly attracted to a magnetic field.
  • Temporary magnetism that dissipates once the external field is gone.

In the example provided earlier, ions like \(\mathrm{H}_{2}^{-}\), \(\mathrm{Ne}_{2}^{+}\), and \(\mathrm{O}_{2}^{2+}\) may exhibit paramagnetism due to unpaired electrons resulting from loss or gain of electrons or splitting in molecular orbitals.

Magnetic Properties

Magnetic properties are essential characteristics that describe how substances respond to an external magnetic field. These properties depend on electron configurations and whether electrons in atoms or molecules are paired or unpaired.Substances can be classified as:

• Diamagnetic: Substances with all paired electrons. These materials are weakly repelled by magnetic fields and do not have intrinsic magnetic moments, whereas paramagnetic or ferromagnetic materials might.
• Paramagnetic: Substances with unpaired electrons that are weakly attracted to magnetic fields, as explained before.
• Ferromagnetic: Substances with unpaired electrons that are attracted strongly to magnetic fields and maintain magnetism even after the external field is removed due to their intrinsic magnetic moments.

Determining the magnetic properties involves examining the electron configurations of the atoms or ions in a substance to identify how they might respond to magnetic fields. In the original exercise, \(\mathrm{F}_{2}\) was identified as diamagnetic since all its electrons are paired, aligning with weak magnetic repulsion from an external field.