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

Statement (a) is incorrect.

Step 1: Understand the question

The question asks us to determine which statement is incorrect about transition elements. We will analyze each option to find the incorrect one.

Step 2: Analyze statement (a)

Statement (a) claims that transition metals in their highest oxidation states exhibit basic character and form cationic complexes. Transition metals often show acidic, rather than basic, character in high oxidation states because they can accept electrons. Therefore, this statement is likely incorrect.

Step 3: Analyze statement (b)

Statement (b) states that for the first five transition elements (Sc to Mn), all 4s and 3d electrons are used in bonding at their highest oxidation states. This is consistent with the known chemical behavior of these elements, as Sc can reach +3, Ti can reach +4, V can reach +5, and Mn can reach +7 oxidation states.

Step 4: Analyze statement (c)

Statement (c) suggests that once the d^5 configuration is exceeded, the tendency to involve all 3d electrons in bonding decreases. As elements exceed the d^5 configuration, stability and half-filled/full-filled subshells phenomena make such elements favor lower oxidation states.

Step 5: Analyze statement (d)

Statement (d) claims that transition elements can also exist in a zero oxidation state. This is true as many transition metals form complexes like carbonyls where the metal is in the zero oxidation state.

Step 6: Conclusion: Identify the incorrect statement

Based on the analysis, statement (a) is incorrect as transition metals in high oxidation states do not display basic character. Statements (b), (c), and (d) are correct regarding the properties of transition elements.

Key Concepts

Oxidation States

Transition elements are known for their ability to exhibit a wide range of oxidation states. This flexibility is due to the similar energy levels of their outer electrons, which can be redistributed to form various oxidation states. Generally, the oxidation state indicates the degree of oxidation of an atom within a compound, represented by a number that shows its potential to gain or lose electrons.

• Lower oxidation states tend to exhibit more metallic or reducing characteristics.
• Higher oxidation states are often linked to acidic behavior, as these states can easily accept additional electrons.
• Intermediate oxidation states, particularly those around +2 and +3, are common in transition elements since they provide a balance between stability and reactivity.

When a transition metal reaches very high oxidation states, such as those observed in Ti\(+4\) or Mn\(+7\), it may demonstrate acidic rather than basic characteristics. This means these metals are more likely to form bonds with complex ligands that donate electrons, such as oxygen or nitrogen species.

Electron Configuration

The electron configuration of an atom is crucial for understanding its chemical behavior, particularly the distribution of electrons across different orbitals. Transition metals have their electrons filling the 3d orbitals, and this configuration plays a significant role in determining their oxidation states.

• The electron configuration can typically be represented as \([noble \ gas] + (n-1)d\) and \((n)s\), where the \(d\) subshell is gradually being filled.
• For the first row of transition elements (Sc to Mn), the 3d and 4s electrons participate in chemical bonding. These elements have electron configurations ranging from Sc: \([ ext{Ar}] 3d^1 4s^2\) to Mn: \([ ext{Ar}] 3d^5 4s^2\).
• As electrons fill these subshells, especially beyond the \(d^5\) configuration, the stability of electronic arrangements becomes a key factor. Elements with half-filled and fully-filled d subshells, like \(3d^5\) and \(3d^{10}\), exhibit significant stability, influencing their chemical reactivity.

Complex Formation

Another fascinating property of transition elements is their remarkable ability to form complexes. Complex formation involves a central metal atom bonded to surrounding molecules or ions, called ligands. This property arises due to their partially-filled d orbitals, which can readily accept electron pairs from ligands.

• Transition metals can form complexes with a variety of oxidation states, including the uncommon zero oxidation state, seen in metal carbonyls.
• The coordination number, which is the number of ligand atoms bonded to the metal, can vary. Common coordination numbers are 4 (tetrahedral, square planar) and 6 (octahedral).
• Complexes have diverse geometries but are usually determined by the electronic configuration and oxidation state of the metal center. This influences the stability and color of the compound.

As a feature of transition elements, these complexes are vital in fields like bioinorganic chemistry, catalysis, and materials science, where they play key roles in processes ranging from oxygen transport to the synthesis of industrial chemicals.