Problem 146 - A Complete Resource Book in Chemistry for JEE Main

Question

In context with the transition elements, which of the following statement is incorrect? (a) In the highest oxidation states, the transition metal show basic character and cationic complex. (b) In the highest oxidation states of the first five transition element (Sc to Mn), all the \(4 \mathrm{~s}\) and \(3 \mathrm{~d}\) electrons are used for bonding. (c) Once the \(\mathrm{d}^{5}\) configuration is exceeded, the tendency to involve all the \(3 \mathrm{~d}\) electrons in bonding decreases. (d) In addition to the normal oxidation states, the zero oxidation state is also shown by these elements in complex.

Step-by-Step Solution

Answer

The incorrect statement is (a).

Step 1: Identify the Incorrect Statement

Read each option carefully to find the incorrect statement regarding the transition elements.

Step 2: Analyze Option (a)

Option (a) suggests that transition metals in their highest oxidation states show basic character and form cationic complexes. Typically, higher oxidation states are associated with acidic or neutral character, meaning this statement is likely incorrect.

Step 3: Analyze Option (b)

Option (b) states that in the highest oxidation states, the first five transition elements use both 4s and 3d electrons for bonding. This is generally a correct statement for Sc to Mn.

Step 4: Analyze Option (c)

Option (c) asserts that beyond the \(d^5\) configuration, the ability to use all 3d electrons for bonding decreases. This is correct because paired electrons and the energy required reduce the likelihood of involving all 3d electrons.

Step 5: Analyze Option (d)

Option (d) suggests that transition elements can also exhibit a zero oxidation state in complexes, which is correct as these metals can bind with ligands without transferring electrons, leading to zero oxidation states.

Key Concepts

Oxidation States

Oxidation states refer to the charge on a metal ion when it forms compounds or complexes. Particularly for transition metals, oxidation states can vary significantly, showcasing their versatile chemistry. This variance arises because these elements can lose varying numbers of electrons from both their outermost "s" and penultimate "d" orbitals.

In transition elements, the oxidation states can range from low values to very high ones. For example, manganese ( Mn) can exhibit states from "+2" up to "+7". Higher oxidation states often correspond to more intensive electron sharing or interaction with surrounding atoms. While in their higher oxidation states, transition metals tend to show acidic character due to the increased pulling of electron density towards themselves.

Also, they can form both cationic and neutral complexes depending on their oxidation state. Cationic complexes typically arise from fully occupied d-orbitals, where metals hold a positive charge. A good understanding of oxidation states is essential as it determines the metal's properties and its reactivity in different chemical environments.

d-Block Elements

Known as the middle section of the periodic table, the d-block elements are characterized by the filling of the "d" orbitals. These elements are renowned for their ability to form multiple oxidation states. This wide array of oxidation states is due to the participation of both 3d and 4s electrons in bonding.

The d-block spans groups 3 to 12 of the periodic table, and includes metals such as iron ( Fe), copper ( Cu), and zinc ( Zn). These elements typically exhibit properties like metallic conduction, the formation of colored compounds and complex ion formation. They are crucial in various biological and industrial processes, such as catalysis and magnetic applications.

Because their d-orbitals are not completely filled, d-block elements demonstrate unique half-filled or fully filled d-orbitals that contribute to stability and distinct chemical behaviors. For example, the presence of unpaired d electrons pervades their ability to participate in different bonding scenarios and respond to magnetic fields.

Transition Metal Complexes

Transition metal complexes consist of a central metal atom or ion surrounded by molecules or ions, known as ligands. These complexes form through coordination bonds, where ligands donate electron pairs to the metal center. Transition metals are particularly suited for this kind of bonding because of their available d-orbitals.

This ability to form complexes is important as it gives transition metals much of their characteristic chemistry, including their variable oxidation states, colors, and magnetic properties. The ligands can be neutral such as water or ammonia, or they can be charged like chloride or cyanide ions. The nature of these ligands influences the metal’s chemical behavior and the stability of the complex.

A unique aspect of transition metal complexes is their ability to exhibit different geometries based on factors like the metal's oxidation state and the types of ligands involved. Common geometries include octahedral, tetrahedral, and square planar arrangements. Studying these complexes offers deep insights into the control of reactivity and selectivity in chemical synthesis and industrial applications.