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 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 Options

Let's look at each of the statements to understand their meanings related to transition elements.

Step 2: Analyze Statement (a)

Statement (a) claims that in the highest oxidation states, transition metals show basic character and form cationic complexes. Transition metals in high oxidation states often form compounds that are more acidic than basic, and they can form both cationic and anionic complexes.

Step 3: Review Statement (b)

Statement (b) refers to the fact that for the first five transition elements, from Sc to Mn, in their highest oxidation states, all their 4s and 3d electrons are used for bonding. This is indeed true.

Step 4: Consider Statement (c)

Statement (c) suggests that once a d^5 configuration is exceeded, the ability to use all 3d electrons in bonding decreases. This is accurate due to the exchange energy stabilization being maximized at d^5.

Step 5: Examine Statement (d)

Statement (d) asserts that transition metals can exhibit a zero oxidation state in complexes. This is a valid statement as many transition metals can form complexes in a zero oxidation state.

Step 6: Determine the Incorrect Statement

Based on the analysis, statement (a) is incorrect as it inaccurately describes the basic character in high oxidation states for transition metals.

Key Concepts

Oxidation States

Transition elements can exhibit various oxidation states. This characteristic is due to their ability to lose different numbers of electrons from both the 4s and 3d subshells. Generally, oxidation states range from +1 to +7 for these elements.
The term "oxidation state" refers to the charge left on the atom after electrons are removed or added to it. For transition metals:

• The 4s electrons are removed first, followed by the 3d electrons.
• High oxidation states are typically found in compounds such as oxides and fluorides.
• In high oxidation states, transition metals often display acidic characteristics, not basic, contrary to what some might think. This is because these metals form covalent bonds in which they share electrons.

Understanding oxidation states is key to predicting the chemical behavior of transition metals.

D-Electron Configuration

The electron configuration of transition elements is significant since it determines their chemical properties. Transition metals are defined by their partially filled d orbitals.

• The electron configuration of these elements largely impacts their stability and reactivity.
• For instance, a d electron configuration such as d⁵ is particularly stable due to half-filled orbital stability and exchange energy.
• This configuration's stability is the reason why the reactivity decreases when transitioning to d⁶ and beyond, as forming very stable configurations becomes less feasible.

Thus, knowing their d-electron configuration helps in understanding their bonding and oxidation states.

Complex Formation

Transition metals are well-known for their ability to form a range of complex compounds. This is a notable feature of their chemistry. A complex is a structure consisting of a central metal atom bonded to surrounding molecules or anions known as ligands:

• Transition metals can form complexes due to their small, highly charged ions and the availability of d orbitals.
• These complexes can be cationic, anionic, or neutral, depending on the metal and the ligands.
• Interestingly, metals in their zero oxidation state can still form stable complexes, showcasing the diversity of their chemistry.

The formation of complexes extends the utility of transition metals in catalysts, biological systems, and industrial applications.