Question

The inert-pair effect is sometimes used to explain the tendency of heavier members of Group 3 \(\mathrm{A}\) to exhibit \(+1\) and \(+3\) oxidation states. What does the inert-pair effect reference? (Hint:Consider the valence electron configuration for Group 3 \(\mathrm{A}\) elements.)

Short answer

The inert-pair effect refers to the tendency of the outermost s-electrons (ns^2) in heavier Group 3A elements to remain unshared in compounds, resulting in a lower oxidation state. As the atomic number increases within the group, this effect becomes more pronounced due to larger size and relativistic effects. This explains the preference of heavier Group 3A elements such as gallium (Ga), indium (In), and thallium (Tl) for exhibiting +1 and +3 oxidation states, as the inert-pair effect causes their s-electrons (ns^2) to be less available for bonding and more difficult to remove than the single p-electron (np^1).

Step-by-step solution

Group 3A elements include boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (Tl). Their general electron configuration can be written as [noble gas core] ns^2 np^1. #Step 2: Consider the Valence Electron Configuration of Heavier Group 3A Elements#

Specifically, look at the configurations for gallium (Ga), indium (In), and thallium (Tl): Gallium: [Ar] 3d^10 4s^2 4p^1 Indium: [Kr] 4d^10 5s^2 5p^1 Thallium: [Xe] 4f^14 5d^10 6s^2 6p^1 Notice that as the elements go down the group, they have more filled d and/or f orbitals in their electron configurations. #Step 3: Explain the Inert-Pair Effect#

The inert-pair effect is the tendency of the outermost s-electrons (ns^2) to remain unshared in compounds, resulting in a lower oxidation state. This effect becomes more pronounced as the atomic number increases within a group, due to larger size and relativistic effects. In heavier Group 3A elements, the inert-pair effect causes the s-electrons (ns^2) to be less available for bonding and more difficult to remove than the single p-electron (np^1). #Step 4: Relate the Inert-Pair Effect to Oxidation States of Heavier Group 3A Elements#

The inert-pair effect explains the tendency of heavier Group 3A elements to exhibit +1 and +3 oxidation states. - In the +3 oxidation state, all three valence electrons (ns^2 np^1) are removed. - In the +1 oxidation state, only the single p-electron (np^1) is removed and the s-electrons (ns^2) remain unshared due to the inert-pair effect. Therefore, the inert-pair effect references the reluctance of the heavier Group 3A elements' outermost s-electrons to participate in bonding, which results in their preference for the +1 oxidation state in addition to the expected +3 state.

Key concepts

Oxidation States

Oxidation states are important to understanding chemical behavior. They refer to the charge an atom would have if all its bonds were completely ionic. For atoms in their natural state, the oxidation state can help us predict how they will interact with other elements. This is especially helpful for understanding why certain elements show a preference for specific oxidation numbers.
In the heavier Group 3A elements such as gallium, indium, and thallium, we've noticed the presence of +1 and +3 oxidation states. This variation is due to the inert-pair effect, wherein the s-electrons are less available for bonding. In the +3 oxidation state, both the ns and np electrons participate in bonding, while in the +1 oxidation state only the p-electron is involved, and the s-electrons are retained as they remain inert. This alteration in behavior as we move down the table is fascinating and plays a critical role in chemistry.

Group 3A Elements

Group 3A elements are a unique section of the periodic table consisting of boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (Tl). These elements share a common electronic structure, typically written as \[ \text{[Noble Gas Core]} \, ns^2 np^1 \].
As you go down this group, each element incrementally takes on more electrons in the d and f orbitals, affecting their chemical properties. Boron is considerably different in behavior compared to its heavier counterparts, which is attributed to its lack of filled d or f orbitals. Meanwhile, heavier elements demonstrate significant traits caused by such filled inner shells. The filled d or f orbitals increase the effectiveness of the shielding effect, making the s-electrons much less reactive and leading to intriguing oxidation numbers.
Understanding how the behavior of these elements changes helps in a wide range of applications, from creating innovative materials to understanding biological processes.

Valence Electron Configuration

The valence electron configuration plays a pivotal role in determining the chemical reactivity and bonding abilities of elements. For Group 3A elements, the general configuration can be simplified as \[ ns^2 np^1 \]. These valence electrons are the outermost and hence take part most actively in chemical reactions.
With heavier Group 3A elements such as gallium \[ (\text{[Ar]} \ 3d^{10} \ 4s^2 \ 4p^1) \, \] indium \[ (\text{[Kr]} \ 4d^{10} \ 5s^2 \ 5p^1) \, \] and thallium \[ (\text{[Xe]} \ 4f^{14} \ 5d^{10} \ 6s^2 \ 6p^1) \], their configurations contain more filled d and f orbitals. This results in increased stability of the ns^2 electrons, making them less likely to participate in bonding. That reluctance is what contributes to the inert-pair effect, leaving these electrons to be more challenging to ionize compared to the single np electron.

• The ns^2 electrons, being less reactive, contribute to the reduced oxidation numbers, aligning with the presence of both +1 and +3 states.

This configuration illustrates how the periodic table's structure predicts the chemistry of elements and helps explain phenomena like the inert-pair effect.