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 \(\mathrm{Mn}\) ), 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: Understanding Transition Metals

Transition elements are metals that have partially filled d-orbital and exhibit a range of oxidation states in their compounds. It is important to understand how these oxidation states influence their chemical behavior.

Step 2: Analyzing Statement (a)

Statement (a) suggests that transition metals show basic character and form cationic complexes in their highest oxidation states. In reality, in the highest oxidation states, transition metals often form covalent and acidic oxides, not basic ones. This makes this statement incorrect.

Step 3: Examining Statement (b)

Statement (b) indicates that the first five transition elements (Sc to Mn) utilize all their 4s and 3d electrons for bonding in their highest oxidation states. This is correct as these elements reach higher oxidation states by using these valence electrons.

Step 4: Reviewing Statement (c)

Statement (c) claims that beyond the d5 configuration, there is a decreasing tendency to involve all 3d electrons in bonding. This is true because after the d5 configuration, additional electron pairing in d orbitals tends to occur, limiting further involvement in bonding.

Step 5: Checking Statement (d)

Statement (d) describes that transition elements can exhibit a zero oxidation state in complexes. This is correct because transition metals can form compounds such as metal carbonyls, where they exhibit a zero oxidation state.

Step 6: Conclusion: Identifying the Incorrect Statement

After evaluating all the statements, Statement (a) is identified as incorrect due to its mischaracterization of the nature of transition metals in their highest oxidation states.

Key Concepts

Oxidation States

Transition elements exhibit a variety of oxidation states, which is a key feature of these metals. This variability arises from the ability to lose different numbers of electrons, particularly from their outer s and d orbitals. At higher oxidation states, transition metals often form compounds like oxides that are generally acidic, highlighting their covalent character, rather than basic.
In contrast, lower oxidation states are typically associated with ionic and less covalent bonds. The variability in oxidation states is one of the reasons why transition metals are so versatile in chemistry. For example, the manganese atom can be found in oxidation states ranging from +2 to +7, which is utilized in its diverse chemical applications.

Transition Metals

Transition metals, found in the central block of the periodic table, are defined by their ability to form stable ions with incomplete d-orbitals. These elements, including well-known metals like iron, copper, and nickel, play a crucial role in various chemical processes due to their unique properties. They are distinguished by a number of characteristics:

• Multiple oxidation states, which allow them to participate in a wide range of reactions.
• The ability to form colored compounds, which is a result of d-d electron transitions.
• The formation of complex compounds, often with distinctive geometries and magnetic properties.

Transition metals are also significant in industrial and biological systems due to their catalytic properties, aiding reactions without being consumed.

d-Orbitals

The d-orbitals play a major role in the chemistry of transition metals. These orbitals can hold up to 10 electrons and are responsible for the complex behaviors exhibited by these elements. The unique shapes and orientations of the d-orbitals allow transition metals to form complex bonds and geometric configurations with other atoms.
The partially filled d-orbitals are also why transition metals can exhibit many oxidation states, as electrons from these orbitals can be involved in bonding. Additionally, the d-electrons can undergo pairing and unpairing, influencing the magnetic and electronic properties of compounds. Once the configuration exceeds a half-filled d-subshell (d extsuperscript{5}), paired electrons can decrease the availability for bonding, impacting the metal's reactivity and the oxidation states it can achieve.

Electron Configuration

The electron configuration of transition metals involves filling of the 4s orbital before the 3d orbital, though during ion formation, electrons are generally lost from the 4s orbital first. This filling order influences the chemical properties and periodic trends observed among these elements.
The noble gas core followed by (n-1)d electrons and ns electrons form the basis of the electron configuration for these elements. As a rule, transition metals have an electron configuration that ends in a partially filled d-subshell, which is key to their rich chemistry.

• This arrangement allows for the flexibility in oxidation states.
• The formation of varied types of chemicals and complexes.
• Participation in diverse catalytic and biochemical processes.

Understanding electron configurations helps explain not just how transition metals interact with other elements, but also the unique roles they play in the broader scope of chemistry.