Problem 14 - Chemistry The Central Science

Question

No compounds are known in which scandium is in the +2 oxidation state. Suggest an explanation.

Step-by-Step Solution

Answer

Scandium generally forms a stable +3 oxidation state by losing three electrons, leading to an electronic configuration similar to the noble gas argon. The +2 oxidation state of scandium would require losing only two electrons, which leaves a less stable electronic configuration with one electron remaining in the 3d subshell. This results in no known compounds with scandium in the +2 oxidation state due to its less favorable electron configuration and reduced stability.

Step 1: Electronic configuration of scandium

Scandium has an atomic number of 21. Its electronic configuration can be written as \(1s^{2}\, 2s^{2}2p^{6}\, 3s^{2}3p^{6}\, 4s^{2}3d^{1}\). This configuration shows that scandium has two electrons in the 4s subshell and one electron in the 3d subshell.

Step 2: Oxidation states

Oxidation states indicate the number of electrons that an atom can gain or lose to form a compound with other elements. The oxidation state of an element can often be predicted by looking at its position in the periodic table and its electronic configuration.

Step 3: Examining +3 oxidation state of scandium

When scandium forms ions, it generally loses three electrons to achieve a stable configuration. These three electrons are the two in the 4s subshell and the one in the 3d subshell. Thus, scandium forms a +3 ion with an electronic configuration \(1s^{2}\, 2s^{2}2p^{6}\, 3s^{2}3p^{6}\) like the noble gas argon, leading to a stable +3 oxidation state.

Step 4: Exploring the +2 oxidation state

If scandium were to form a +2 oxidation state, it would have to lose only two electrons, leaving one electron in the 3d subshell. The resulting ion would have an electronic configuration of \(1s^{2}\, 2s^{2}2p^{6}\, 3s^{2}3p^{6}\, 3d^{1}\). This configuration is less stable than the one with a +3 oxidation state, as the remaining electron in the 3d subshell is not energetically favorable.

Step 5: Conclusion

Scandium tends to achieve a more stable electronic configuration by losing three electrons, resulting in a +3 oxidation state. The +2 oxidation state, which would require only losing two electrons, leaves an unfavorable electron configuration with less stability. Therefore, no known compounds with scandium in the +2 oxidation state exist.

Key Concepts

Scandium

Scandium is a fascinating metal found in the periodic table with the symbol \( \text{Sc} \) and an atomic number of 21. It belongs to the group of transition metals, which are known for their ability to form various oxidation states. Scandium is relatively rare and has some unique characteristics. It typically appears in compounds in a +3 oxidation state, which we will explore in more detail later. Despite its rarity, scandium is used in some niche applications, such as in the manufacturing of aerospace components due to its lightweight and strong properties.

Electronic Configuration

The electronic configuration of an element determines how its electrons are distributed in various atomic orbitals. For scandium, its electronic configuration is crucial in understanding its chemical behavior. Scandium's electronic configuration is written as \(1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 4s^{2} 3d^{1}\). This shows us the arrangement of electrons in its orbitals:

• the first two electrons are in the \(1s\) orbital,
• followed by two in the \(2s\) orbital,
• six in the \(2p\) orbital,
• two in the \(3s\) orbital,
• six in the \(3p\) orbital,
• two in the \(4s\) orbital, and
• one in the \(3d\) orbital.

When scandium forms ions, it tends to lose electrons to achieve a more stable electronic configuration, which we will discuss in connection with its oxidation states.

Transition Metals

Transition metals are a group of elements found in the center of the periodic table, and scandium is a member of this group. These metals are characterized by having partially filled \(d\) orbitals, which allows them to have various oxidation states and form complex ions. This is crucial for their roles in many chemical reactions, catalysis, and materials science.

Scandium, like other transition metals, exhibits variable oxidation states because of its ability to lose different numbers of electrons. It most commonly forms a +3 ion by losing one \(3d\) and two \(4s\) electrons. Despite being a transition metal, scandium's chemistry is more limited compared to others like iron or copper due to its high affinity for a +3 state.

Stability of Oxidation States

The concept of oxidation states is central to understanding scandium's behavior in compounds. An oxidation state indicates how many electrons an atom has gained or lost in a compound. For scandium, the stable oxidation state is +3. Its electronic configuration changes to \(1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6}\) after losing three electrons, becoming similar to argon, a noble gas. This stable configuration provides low energy, which is highly desirable in nature.

It would be energetically unfavorable for scandium to achieve a +2 oxidation state, as it would leave one electron in the \(3d\) orbital resulting in an unstable one compared to releasing all three and achieving a noble gas-like configuration. This instability explains why scandium hardly forms any +2 compounds, as the energy balance heavily favors the stable and energetically efficient +3 state.