Question

Which of the following metals does not show inert pair effect? (a) Thallium (b) Gallium (c) Indium (d) Aluminium

Short answer

Aluminium (d) does not show the inert pair effect.

Step-by-step solution

- Understand Inert Pair Effect

The inert pair effect refers to the reluctance of the s-electrons (specifically, the pair of electrons in the s-orbital) of the valence shell to participate in the bond formation. It is commonly observed in heavy p-block elements (post-transition metals) of groups 13, 14, and 15, leading to the stability of lower oxidation states.

- Identify the Group 13 Elements

From the given options, identify the elements that belong to Group 13, as inert pair effect is a characteristic of certain p-block elements. Thallium (Tl), Gallium (Ga), and Indium (In) are members of Group 13, while Aluminium (Al) also belongs to this group.

- Consider the Periodic Table Trends

The intensity of the inert pair effect increases with increasing atomic number within a group. The effect is more significant in heavier elements as they have more electron shells and the valence electrons experience a greater shielding effect.

- Determine the Element Without Inert Pair Effect

Aluminium (Al) is the lightest among the options and the one with the least tendency to display the inert pair effect. Since it is located in the second period of the periodic table, it does not show inert pair effect which is more prominent in heavier elements of the same group.

Key concepts

Exploring P-Block Elements

P-block elements occupy the region on the right side of the periodic table, spanning Groups 13 to 18. They are characterized by the presence of valence electrons in p-orbitals. One fascinating aspect of these elements is their diverse range of oxidation states, which contributes to their wide array of chemical behaviors.

Within the p-block, elements like Gallium (Ga), Indium (In), and Thallium (Tl) exhibit an interesting phenomenon known as the ‘inert pair effect’. This effect is a reluctance of the s-electrons in the valence shell to participate in chemical bonding, often leading these heavier elements to favor lower oxidation states over what might be expected from their position in the periodic table.

When comparing the members of Group 13, Thallium (Tl) displays the inert pair effect most prominently, resulting in a stable +1 oxidation state alongside the expected +3. This highlights the complex and unpredictable nature of p-block chemistry, influenced by not just electronic configurations but also the effects of atomic size, relativistic effects, and electron shielding.

Oxidation States and Their Stability

Understanding oxidation states is pivotal in predicting the behavior and reactivity of elements. In essence, the oxidation state denotes the total number of electrons an atom loses, gains, or shares when it forms chemical bonds. For the p-block elements, the availability and energy of the outer s and p orbitals shape the potential oxidation states an element can adopt.

In our context of the inert pair effect, the reluctance of the s-electron pair to participate in bonding means that the heavier p-block elements often prefer to remain in oxidation states that are two units fewer than their group valency. For example, Thallium (Tl) may often be found in a +1 oxidation state rather than the +3 that might be expected from its position in Group 13.

The stability of these oxidation states is influenced by the atomic structure of the element. In lighter elements like Aluminium (Al), the s-electrons are held closely by the nucleus, and the energy required to involve them in bonding is easily overcome. However, in heavier elements, stronger relativistic effects and increased electron shielding lead to a stronger inert pair effect, stabilizing lower oxidation states.

Periodic Table Trends and Their Influence

The periodic table is a master key to unlocking the behavior of the elements. Trends across the table help us predict characteristics like reactivity, electron affinity, ionization energy, and as relevant here, the inert pair effect. This effect becomes more pronounced with heavier elements, which are found further down a group in the periodic table.

As we move down a group, the atoms' radii increase due to additional electron shells. This increase in size means that the inner electrons shield the outermost electrons from the nucleus's pull more effectively. When this shielding becomes significant, the valence s-electrons are less readily available for bonding, thus marking the inert pair effect.

Aluminium (Al), the element in question for being least affected by the inert pair effect, resides in the second period where the effect of electron shielding is minimal. Hence, Al readily exhibits its expected +3 oxidation state by involving all its outer electrons in bonding. By contrast, heavier congeners like Thallium prefer lower oxidation states because their valence s-electrons experience greater shielding and are more ‘inert’. Understanding these trends is not just about memorization—it's about appreciating the inherent physics of atoms and how their structure dictates their chemistry.