Problem 14 - A Complete Resource Book in Chemistry for JEE Main

Question

Among the following series of transition metal ions, the one where all metal ions have \(3 \mathrm{~d}^{2}\) electronic configuration is (a) \(\mathrm{Ti}^{+}, \mathrm{V}^{4+}, \mathrm{Cr}^{6+}, \mathrm{Mn}^{7+}\) (b) \(\mathrm{Ti}^{2+}, \mathrm{V}^{3+}, \mathrm{Cr}^{4+}, \mathrm{Mn}^{3+}\) (c) \(\mathrm{Ti}^{3+}, \mathrm{V}^{2+}, \mathrm{Cr}^{3+}, \mathrm{Mn}^{4+}\) (d) \(\mathrm{Ti}^{4+}, \mathrm{V}^{3+}, \mathrm{Cr}^{2+}, \mathrm{Mn}^{3+}\)

Step-by-Step Solution

Answer

None of the options have all ions with a 3d² configuration.

Step 1: Understand the Electronic Configuration

For an element in the periodic table, the atomic number informs us about the distribution of electrons across orbitals. Transition metals primarily fill their 3d orbitals.

Step 2: Determine the Neutron State

The series question specifies, for each ion, checking the electron configuration to ensure the 3d sublevel contains exactly 2 electrons.

Step 3: Analyze Option (a)

For Ti⁺, the atomic number is 22, so the neutral atom is [Ar] 3d² 4s², losing one becomes [Ar] 3d² 4s¹, but Ti⁺ simplifies to 3d². V⁴⁺, atomic number 23, follows [Ar] 3d³ 4s², losing four yields [Ar]. Cr⁶⁺ follows atomic 24, from [Ar] 3d⁵ 4s¹ loses six to [Ar]. Mn⁷⁺ follows atomic 25 from [Ar] 3d⁵ 4s² loses seven to [Ar]. All but Ti don't have 3d², eliminating this option.

Step 4: Analyze Option (b)

Ti²⁺ from [Ar] 3d² 4s² loses two to [Ar] 3d². V³⁺ from [Ar] 3d³ 4s² loses three to [Ar] 3d². Cr⁴⁺ goes from [Ar] 3d⁵ 4s¹ losing four to [Ar] 3d². Mn³⁺ goes from [Ar] 3d⁵ 4s² losing three to [Ar] 3d⁴. Not all have 3d².

Step 5: Analyze Option (c)

For Ti³⁺, [Ar] 3d² 4s² becomes [Ar] 3d¹. V²⁺ goes from [Ar] 3d³ 4s² to [Ar] 3d³. Cr³⁺ [Ar] 3d⁵ 4s¹ becomes [Ar] 3d³. Mn⁴⁺ [Ar] 3d⁵ 4s² becomes [Ar] 3d³. Not all have 3d².

Step 6: Analyze Option (d)

Ti⁴⁺ with [Ar] 3d² 4s² to [Ar], zero d. V³⁺ from [Ar] 3d³ 4s² becomes [Ar] 3d² after three lost. Cr²⁺ [Ar] 3d⁵ 4s¹ becomes [Ar] 3d³. Mn³⁺ [Ar] 3d⁵ 4s² becomes [Ar] 3d⁴. Does not meet the condition.

Step 7: Confirm the Correct Series

Review all ions' electron configurations: only option (b) gives all elements with electronic configurations adjacent to having d orbitals remaining but slightly higher. Option (b) doesn't fit 3d² for all either.

Key Concepts

Electronic Configuration

Electronic configuration refers to the arrangement of electrons in an atom's orbitals. It is primarily governed by the principles of quantum mechanics. For transition metals, electrons fill the 3d orbitals after the 4s orbitals. This means, for example, that in a neutral titanium atom, the electronic configuration would be

• 1s² 2s² 2p⁶ 3s² 3p⁶ 3d² 4s² or,
• [Ar] 3d² 4s²,

where [Ar] represents the electron configuration of argon. As electrons are removed (or added), this configuration changes, which affects the chemical properties of the element. For ions, electrons are preferentially removed from the outermost shell first, which often means the 4s electrons are lost before the 3d electrons.

3d Orbitals

The 3d orbitals are a set of five orbitals in the d subshell with a principal quantum number of 3. These orbitals are filled with electrons after the 4s orbital in the atoms of the transition metals.
Each d orbital can hold a maximum of two electrons, so a complete 3d subshell can hold up to ten electrons. The filling of these orbitals influences the geometry and magnetic properties of the atoms.
When transition metal ions are formed, the electrons in the 3d subshell play a significant role. For example, for the transition metal ions mentioned in the exercise:

• Ti²⁺ has an electron configuration of [Ar] 3d², indicating that the two 3d electrons remain after losing the 4s electrons.
• The role of d orbitals becomes even more significant in the bonding and chemical behavior of the elements.

These metal ions exhibit various oxidation states due to the involvement of these d electrons.

Ionization States

Transition metal atoms can lose different numbers of electrons to form positive ions or cations, resulting in different ionization states. The oxidation state or ionization state is the total number of electrons removed.
These states are pivotal in determining the chemical reactivity and coordination properties of the ions. For example, in the transition metal series question, the ions Ti²⁺, V³⁺, Cr⁴⁺, and Mn³⁺ exhibit different positive ionization states depending on how many electrons have been removed.

• The ionization states can complicate the electron configuration since electrons from the 3d orbitals and 4s orbitals can be involved.
• Higher ionization states generally mean more electrons have been removed, typically from the 4s before the 3d orbitals.

By understanding ionization states, students can predict and explain the behavior of transition metals in chemical reactions and distinguish between different ions of the same element based on their electronic configurations.