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.)

The Group 3A elements are: 1. Boron (B): Atomic number 5 and electron configuration: 1s² 2s² 2p¹ 2. Aluminum (Al): Atomic number 13 and electron configuration: 1s² 2s² 2p⁶ 3s² 3p¹ 3. Gallium (Ga): Atomic number 31 and electron configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p¹ 4. Indium (In): Atomic number 49 and electron configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p¹ We will focus on the valence electron configurations for these elements.

We can determine the valence electron configurations for Group 3A elements by looking at their outermost electron configurations: 1. Boron (B): 2s² 2p¹ 2. Aluminum (Al): 3s² 3p¹ 3. Gallium (Ga): 4s² 3d¹⁰ 4p¹ 4. Indium (In): 5s² 4d¹⁰ 5p¹ Now we will describe how the inert-pair effect is related to the different valence electron configurations.

The inert-pair effect refers to the tendency of heavy atoms' ns² electrons (where n is the principal quantum number) to be less involved in chemical reactions. This is due to the increased shielding effect and poor overlap with other orbitals caused by the presence of full d orbitals (as in Ga and In). As a result, the outermost s electrons are less likely to participate in the atom's bonding and oxidation state. In Group 3A elements, the s² electrons are the ones affected by the inert-pair effect, which influences the element's tendency to exhibit different oxidation states. For lighter elements (B and Al), their s² electrons are more likely to participate in bonding, and their common oxidation state is +3. For heavier elements (Ga and In), the presence of full d orbitals causes the inert-pair effect to become more significant. As a result, they can exhibit both +1 and +3 oxidation states, depending on whether the s² electrons are involved in chemical reactions. In conclusion, the inert-pair effect in Group 3A elements refers to the reduced participation of ns² valence electrons in heavier elements' bonding and chemical reactions due to increased shielding and poor overlap caused by full d orbitals. This results in the heavier elements being able to exhibit both +1 and +3 oxidation states.