Problem 111 - 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 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. In 3 d-series, the maximum oxidation state is shown by (a) \(\mathrm{Fe}(26)\) (b) Mn (atomic no. : 25 ) (c) \(\mathrm{Cr}(24)\) (d) Sc (atomic no : 21 )

Step-by-Step Solution

Answer

Manganese (Mn) shows the highest oxidation state of +7.

Step 1: Understand the Question

We need to determine which element from the given options in the 3d-transition series shows the maximum oxidation state based on the involvement of (n-1)d and outer ns electrons.

Step 2: Identify the Elements and their Electron Configurations

Consider the elements provided and their electron configurations. For 3d transition metals, electrons generally fill the 4s orbital before the 3d. The elements with their atomic numbers are: 1. Scandium (Sc) - 21: [Ar] 3d¹ 4s² 2. Chromium (Cr) - 24: [Ar] 3d⁵ 4s¹ 3. Manganese (Mn) - 25: [Ar] 3d⁵ 4s² 4. Iron (Fe) - 26: [Ar] 3d⁶ 4s².

Step 3: Determine Maximum Oxidation State

The maximum oxidation state of an element is equal to the sum of its 4s and 3d electrons. 1. Scandium (Sc) = 3 (2 from 4s + 1 from 3d) 2. Chromium (Cr) = 6 (1 from 4s + 5 from 3d) 3. Manganese (Mn) = 7 (2 from 4s + 5 from 3d) 4. Iron (Fe) = 6 (2 from 4s + 4 from 3d).

Step 4: Compare Oxidation States

From the calculations, Manganese (Mn) has the highest oxidation state of +7, followed by Chromium (Cr) and Iron (Fe) with +6, and finally Scandium (Sc) with +3.

Key Concepts

Transition Metals

Transition metals are fascinating elements that occupy the d-block of the periodic table. This group encompasses elements that have partially filled d orbitals, which grant them unique properties.
A hallmark of transition metals is their ability to exhibit multiple oxidation states. This means they can lose different numbers of electrons during reactions, leading to a variety of stable ionic forms. This trait arises because transition metals have both their outer shell (s electrons) and the nearby (n-1)d orbitals involved in bonding.
Another fascinating aspect is that many transition metals are capable of forming colorful compounds.
Colors arise from electron transitions between d-orbitals of differing energies. Interesting to note, these elements are also characterized by having high melting points and densities.
These properties are due to the strong metallic bonding brought about by the delocalized d electrons. All of these characteristics make transition metals an essential topic in the study of chemistry.

3d-Transition Series

The 3d-transition series includes 10 elements ranging from Scandium (Sc) to Zinc (Zn) in the periodic table.
This series marks the first row of transition metals and is crucial for understanding the properties that define transition metals.
In the context of electron configurations, these elements fill the 3d orbitals as you move across the period.
Starting with Scandium, which has an electron configuration of \[\text{[Ar]}\ 3d^1\ 4s^2\], the 3d orbitals progressively gain electrons until they are fully filled at Zinc \[\text{[Ar]}\ 3d^{10}\ 4s^2\].
The ability to form variable oxidation states is particularly pronounced in these elements due to the similar energy levels of the 3d and 4s orbitals.
Understanding the 3d-transition series is essential for grasping how properties like magnetism and catalytic behaviors arise, shaping their use in various industrial applications.

Electron Configuration

The electron configuration of an element reveals a great deal about its chemical behavior and properties.
For transition metals, the arrangement of electrons between the ns and (n-1)d orbitals plays a crucial role.
Generally, electrons fill the 4s orbital before the 3d; however, this can vary due to the subtle energy differences and stability factors.
For example, the electron configuration of Chromium, \[\text{[Ar]}\ 3d^5\ 4s^1\], is an exception due to half-filled stability which takes precedence over filling the 4s completely.
Similarly, Manganese, with \[\text{[Ar]}\ 3d^5\ 4s^2\], therefore showcases a standard filling order.
Such configurations help predict chemical reactivity, the formation of complexes, and magnetic properties, making them a foundational subject in inorganic chemistry.

Variable Oxidation States

One of the most defining characteristics of transition metals is their ability to exhibit variable oxidation states.
This flexibility results from the involvement of both ns and (n-1)d electrons in bond formation and removal.
Elements can adjust their oxidation number depending on the type of chemical reaction they undergo.

• Scandium as \[\text{[Ar]}\ 3d^1\ 4s^2\], for instance, typically shows a +3 oxidation state.
• Iron often presents multiple states like +2 and +3, due to the valence electrons from the 4s and 3d levels.
• Manganese can reach a high oxidation state of +7.

The ability to display multiple oxidation states enables these metals to serve as catalysts in various processes by adopting different ionic forms, thus facilitating complex chemical transformations.