Parmi les ions suivants, lesquels ne sont pas l'ion

Parmi les ions suivants, lesquels ne sont pas l'ion « le plus stable» (ou « ion normal ») de l'élément correspondant? $\mathrm{Li}^{-} \mathrm{Al}^{2+} \mathrm{S}^{2-} \mathrm{K}^{+} \quad \mathrm{Rb}^{2+} \mathrm{Zn}^{2+} \mathrm{Fe}^{2+} \mathrm{Mn}^{7+} \mathrm{Cl}^{2-} \mathrm{l}^{-} \quad \mathrm{Ca}^{+} \quad \mathrm{Ba}^{2+}$

Parmi les ions suivants, lesquels ne sont pas l'ion « le plus stable» (ou « ion normal ») de l'élément correspondant?
$\mathrm{Li}^{-} \mathrm{Al}^{2+} \mathrm{S}^{2-} \mathrm{K}^{+} \quad \mathrm{Rb}^{2+} \mathrm{Zn}^{2+} \mathrm{Fe}^{2+} \mathrm{Mn}^{7+} \mathrm{Cl}^{2-} \mathrm{l}^{-} \quad \mathrm{Ca}^{+} \quad \mathrm{Ba}^{2+}$

Key Concepts

Common Oxidation States

This concept refers to the typical ionic charges that elements adopt in order to achieve a stable electron configuration. Atoms generally gain or lose electrons to emulate the electron configuration of the nearest noble gas, leading to well?known oxidation states (for instance, alkali metals commonly form +1 ions while halogens form -1 ions). Deviations from these common states indicate ionic forms that are less stable or ‘non?normal’ for the element.

Electronic Configuration and the Noble Gas Rule

Ionic stability is largely influenced by the attainment of a noble gas electron configuration, which is particularly stable due to its complete valence shell. When an atom reaches this configuration by either losing or gaining electrons, the resulting ion is considered ‘normal’. Ions that do not lead to achieving a noble gas configuration are typically less stable and are not the preferred state in chemical reactions.

Periodic Trends and Ion Formation

Periodic trends explain why elements tend to form ions with specific charges based on their positions in the periodic table. Metals, located on the left side, tend to lose electrons while non-metals, positioned on the right side, tend to gain electrons. These trends help determine the ‘normal’ or most stable ion for an element and also explain why ions with unexpected charge numbers are uncommon.

Ion Stability and Energy Considerations

The relative stability of an ion is determined by the energy changes associated with electron loss or gain. The formation of the most stable ion typically involves a favorable energy balance, wherein the ion achieves a low-energy state. Ions that do not conform to these energetically favorable states are considered less stable because they do not result in the most complete or advantageous electron configuration.

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