Problem 113 - A Complete Resource Book in Chemistry for JEE Main

Question

The transition elements with some exceptions can show a large number of oxidation states. The various oxidation states are related to the electronic configuration of their atoms. The variable oxidation states of a transition metal is due to the involvement of \((\mathrm{n}-1) \mathrm{d}\) and outer \(\mathrm{ns}\)-electrons. For the first five elements of 3 d-transition series. The minimum oxidation state is equal to the number of electrons in 4s shell and the maximum oxidation state is equal to the sum of \(4 \mathrm{~s}\) and \(3 \mathrm{~d}\)-electrons. The relative stability of various oxidation state of a given element can be explained on the basis of stability of \(\mathrm{d}^{0}, \mathrm{~d}^{5}\) and \(\mathrm{d}^{10}\) configurations. Identify the correct statement (a) \(\mathrm{Ti}^{4+}, \mathrm{Mn}^{2+}\) are stable oxidation states (b) The most common oxidation state of 3 d-series is \(+2\) (c) The lowest oxidation state of \(\mathrm{Cr}\) and \(\mathrm{Cu}\) is \(+1\) while for others it is \(+2\). (d) All of these

Step-by-Step Solution

Answer

Option (d) All of these are correct statements.

Step 1: Understand the Basics of Oxidation States

Transition elements exhibit a variety of oxidation states due to the involvement of both \(n-1\)d and ns electrons. The number of these electrons that an atom can lose or share determines its oxidation state.

Step 2: Identify the Given Transition Elements

The elements of interest here are the first five elements in the 3d transition series: Scandium (Sc), Titanium (Ti), Vanadium (V), Chromium (Cr), and Manganese (Mn). The question also mentions Copper (Cu).

Step 3: Evaluate Minimum and Maximum Oxidation States

For 3d transition metals, the minimum oxidation state is typically the number of electrons in the 4s subshell, and the maximum oxidation state is the sum of 3d and 4s electrons. For example, Ti has 2 electrons in 4s and 2 in 3d, so its maximum is +4. Mn has 2 electrons in 4s and 5 in 3d, so the maximum is +7.

Step 4: Assess Stability of Specific Oxidation States

Evaluate which oxidation states are stable based on the electronic configuration and stability of \(d^0, d^5, \) and \(d^{10}\) configurations. For example, Mn\(^{2+}\) has a \(d^5\) configuration, which is stable, and Ti\(^{4+}\) reaches \(d^0\).

Step 5: Evaluate the Options Given

(a) Ti\(^{4+}\) and Mn\(^{2+}\) are stable. (b) Most common oxidation state for transition metals is +2, as they typically lose their 4s electrons. (c) The lowest oxidation states for Cr and Cu are indeed +1, while for others like Sc, Ti, V, Mn, the lowest is +2.

Key Concepts

Electronic Configuration

In transition elements, electronic configuration refers to the distribution of electrons among the orbitals of an atom. For elements in the 3d transition series, electrons fill up the 3d and 4s orbitals. Typically, electrons occupy the 4s orbital before filling the 3d orbital when building up the electronic configuration. This filling order impacts an element’s chemical properties, including its oxidation states. Electrons in these orbitals can move about and exchange places, influencing which oxidation states are most stable and frequently observed.

3d Transition Series

The 3d transition series consists of the first row of transition metals located between Scandium and Zinc in the periodic table. These elements are characterized by the gradual filling of the 3d subshell.

• These metals exhibit various oxidation states, which can be explained by the number of electrons available in the 3d and 4s orbitals.
• Through this series, metals can exhibit oxidation states ranging from +1 to +7.

The availability of d-electrons in addition to s-electrons provides a range of valences that allows these metals to form complex ions and participate in various chemical reactions.

Variable Oxidation States

The ability of transition metals to exhibit more than one oxidation state stems from the involvement of both (n-1)d and ns electrons in bond formation. Variable oxidation states are fundamental in dictating how these metals engage in compounds and reactions. - The minimum oxidation state is often equivalent to the number of 4s electrons. - The maximum is a total of both the 4s and 3d electrons, which allows the metals to showcase a rich chemistry of transformation. This behavior is why we observe such a wide range of oxidation states in these metals, impacting their reactivity and applications.

Stability of Oxidation States

The stability of oxidation states in transition elements is influenced largely by their electronic configuration.

For instance, configurations with half-filled ( d5) or fully filled (d10) d orbitals exhibit notable stability due to symmetrical electron distribution and exchange energy.

As a case, Ti4+ is stable because it achieves a d0 state, losing all 3d and 4s electrons. Similarly, Mn2+ is stable with a d5 configuration.

These stable states often appear more frequently in nature and lead to distinctive chemical behaviors. Understanding the stability leads us to predict which oxidation states are feasible under different environmental conditions.