Question

Which of the following ions are unlikely to be found in chemical compounds: \(\mathrm{K}^{+}, \mathrm{Ga}^{4+}, \mathrm{Fe}^{6+} \mathrm{S}^{2-}, \mathrm{Ge}^{5+},\) or \(\mathrm{Br}^{-} ?\) Explain briefly.

Short answer

The ions \(Ga^{4+}\), \(Fe^{6+}\), and \(Ge^{5+}\) are unlikely to be found in chemical compounds as these are not their common oxidation states.

Step-by-step solution

Determine the Common Oxidation States

Evaluate each ion and determine the most common oxidation states. This information can usually be found in a periodic table. For the given ions, K usually forms \(K^{+}\), Ga usually forms \(Ga^{3+}\), Fe usually forms \(Fe^{2+}\) or \(Fe^{3+}\), S usually forms \(S^{2-}\), Ge forms \(Ge^{4+}\), and Br usually forms \(Br^{-}\).

Identify Uncommon Oxidation States

Compare the given ions with their common oxidation states. Here, \(Ga^{4+}\), \(Fe^{6+}\), and \(Ge^{5+}\) are not normally found because gallium, iron, and germanium do not usually lose or gain that many electrons to achieve these states. Losing or gaining such amounts of electrons would require a large amount of energy and result in a less stable ion.

Conclusion

From the analysis, \(Ga^{4+}\), \(Fe^{6+}\), and \(Ge^{5+}\) are unlikely to be found in chemical compounds due to their uncommon oxidation states.

Key concepts

Chemical Compounds

Chemical compounds are substances formed when two or more elements chemically bond together. These elements can form ionic or covalent bonds, creating compounds with unique properties different from the individual elements. Ionic bonds usually form between metals and non-metals, where electrons are transferred from one atom to another, leading to the creation of ions. On the other hand, covalent bonds involve the sharing of electron pairs between atoms. Understanding how these bonds work is essential, as it determines the stability and structure of a compound. For example, in the compound KBr, potassium (K) loses an electron to become a cation (\( \text{K}^+ \)), and bromine (Br) gains an electron to become an anion (\( \text{Br}^- \)), creating a stable ionic compound.

Ion Stability

Ion stability is a crucial concept in chemistry, determining how likely an ion is to exist or participate in chemical reactions. Stable ions form when they reach an electronic configuration that resembles the nearest noble gas. For example, potassium (\( \text{K}^+ \)), with one electron less, achieves a configuration similar to argon, a noble gas, making it stable.

• Stable ions typically result from either the full or half-full filling of electron shells, minimizing the amount of energy required to form the ion.
• Unstable ions, like those with uncommon oxidation states, require a lot more energy to form due to extra electrons being removed or added beyond the typical capacity.
• This affects the likelihood of such ions existing in compounds, as demonstrated by \( \text{Ga}^{4+} \) and \( \text{Fe}^{6+} \).

The more energy required to form an ion, the less stable and less likely it is to form a part of a chemical compound.

Periodic Table

The periodic table is a powerful tool for predicting the properties and behaviors of elements, including their likely oxidation states.

• Each element in the table is arranged in order of increasing atomic number, and grouped into columns based on similar chemical properties or valence electron configuration.
• The position of an element in the periodic table gives clues about its reactivity, oxidation state tendencies, and how it might interact with other elements.
• For instance, alkali metals like potassium (K) are in Group 1, indicating that they typically form +1 ions to achieve noble gas configurations.
• Conversely, transition metals, such as iron (Fe), can exhibit multiple oxidation states depending on circumstances, like \( \text{Fe}^{2+} \)
  and \( \text{Fe}^{3+} \).

Understanding trends in the periodic table helps in predicting which ions are more likely to exist.

Common Oxidation States

Common oxidation states are those electron configurations that elements most frequently adopt in stable compounds. Each element generally tends to form certain ions over others due to energy considerations and electronic structure.

• The oxidation state is a number indicating the total number of electrons an atom either gains or loses to form a bond.
• Some elements, like gallium, typically form \( \text{Ga}^{3+} \), not \( \text{Ga}^{4+} \), which is uncommon and entails high energy requirements.
• Uncommon oxidation states are less likely to be found due to increased energy required for such electron configurations, leading to instability.
• Elements like sulfur (S), often found as \( \text{S}^{2-} \), happily follow trends to reach a nearby noble gas configuration.

Knowing common oxidation states allows chemists to predict the most likely and stable forms of elements in chemical compounds.