Problem 95 - A Complete Resource Book in Chemistry for JEE Main

Question

Amongst the following, the lowest degree of paramagnetism per mole of the compound at \(298 \mathrm{~K}\) will be shown by (a) \(\mathrm{MnSO}_{4} \cdot 4 \mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O}\) (c) \(\mathrm{FeSO}_{4} \cdot 6 \mathrm{H}_{2} \mathrm{O}\) (d) \(\mathrm{NiSO}_{4} \cdot 6 \mathrm{H}_{2} \mathrm{O}\)

Step-by-Step Solution

Answer

CuSO₄·5H₂O has the lowest paramagnetism with 1 unpaired electron.

Step 1: Understand Paramagnetism

Paramagnetism is a property of substances that have unpaired electrons. The more unpaired electrons a compound has, the higher its paramagnetism. Therefore, to determine which compound has the lowest degree of paramagnetism, we need to find the number of unpaired electrons in each compound.

Step 2: Determine the Electronic Configuration

We need to determine the electronic configuration of the metal ions in each compound. This helps us count the unpaired electrons: (a) Mn²⁺: [Ar] 3d⁵ (b) Cu²⁺: [Ar] 3d⁹ (c) Fe²⁺: [Ar] 3d⁶ (d) Ni²⁺: [Ar] 3d⁸

Step 3: Count the Unpaired Electrons

Now, count the unpaired electrons in each of these: (a) Mn²⁺: 5 unpaired electrons in the 3d-orbitals (b) Cu²⁺: 1 unpaired electron in the 3d-orbitals (c) Fe²⁺: 4 unpaired electrons in the 3d-orbitals (d) Ni²⁺: 2 unpaired electrons in the 3d-orbitals

Step 4: Identify Lowest Paramagnetism

Compare the number of unpaired electrons. The compound with the least number of unpaired electrons will exhibit the lowest degree of paramagnetism. Thus, the compound is (b) CuSO₄·5H₂O with 1 unpaired electron.

Key Concepts

Unpaired Electrons

Unpaired electrons are electrons within an atom that do not share an orbital with another electron, thus remaining solitary. These types of electrons are significant when discussing paramagnetism—a property that refers to the attraction of a substance to an external magnetic field. In general, the more unpaired electrons a substance has, the stronger its paramagnetic properties. This is because unpaired electrons have magnetic moments that are not canceled out, which allows them to interact with external magnetic fields. For example, when evaluating the paramagnetic behavior of different compounds, it's essential to determine how many unpaired electrons each specific ion in the compound possesses. If we look at the example of transition metal ions, their behavior in terms of paramagnetism can largely be predicted by counting the number of these solitary electrons.

Electronic Configuration

Electronic configuration refers to the arrangement of electrons in an atom or ion and is essential for determining its chemical behavior and properties. For transition metals, this configuration is especially important as it affects the overall stability and reactivity of the ions they form. To understand electronic configurations, it is crucial to know how electrons fill available orbitals around an atom's nucleus:

• Electrons fill the lowest energy orbitals first (following the Aufbau principle).
• Each orbital can hold a maximum of two electrons with opposite spins (Pauli Exclusion Principle).
• Electrons will fill empty orbitals within the same subshell before pairing up (Hund’s Rule).

For example, the electronic configuration of the ext{Mn}^{2+} ion is ext{[Ar] 3d⁵}, indicating that there are five unpaired electrons in the three- ext{d} orbitals. Understanding these configurations helps in predicting both the magnetic properties and other chemical behaviors of the element or compound.

Transition Metal Ions

Transition metal ions are ions formed by elements found in the d-block of the periodic table. These elements are known for having partially filled d-orbitals, which give rise to their unique properties, including various oxidation states and the ability to form colored compounds. Transition metals can lose electrons from their s and d orbitals when forming positive ions. This leads to a variety of electronic configurations, which in turn affects their chemistry and magnetic properties. For example, the transition metal ion ext{Cu}^{2+} has an electronic configuration of ext{[Ar] 3d⁹}, leading to one unpaired electron. This characteristic explains its paramagnetic property, albeit weakly because it has fewer unpaired electrons compared to other ions. Transition metal ions like this play a pivotal role in the chemical and physical properties of compounds, influencing factors such as color, reactivity, and magnetic behavior.