Ion Formation and Periodic Trends Notes

Ion Formation

  • In chemical processes, the nucleus remains unchanged; electrons can be added, removed, or shared.
  • Ions form when atoms gain or lose electrons; metals tend to form cations, nonmetals tend to form anions.
  • Metals lose electrons to reach the electron configuration of the preceding noble gas; nonmetals gain electrons to reach the configuration of the next noble gas.
  • Common ion-charge patterns (main-group):
    • Group 1 forms 1+1^+ ions
    • Group 2 forms 2+2^+ ions
    • Group 17 forms 1−1^- ions
    • Group 16 forms 2−2^- ions
  • Trend limitations:
    • The pattern is most reliable for main-group elements; transition metals and some metals have variable charges.
    • Example variability: Cu+\mathrm{Cu}^{+} or Cu2+\mathrm{Cu}^{2+}; Fe2+\mathrm{Fe}^{2+} or Fe3+\mathrm{Fe}^{3+}
  • Driving principle:
    • Atoms gain or lose electrons to achieve the same electron count as the nearest noble gas.

Example: Noble-gas electron-count alignment

  • Magnesium loses two electrons to attain the same electron count as neon: Mg→Mg2++2e−\mathrm{Mg} \rightarrow \mathrm{Mg}^{2+} + 2e^-
  • Fluorine gains one electron to attain the same electron count as neon: F+e−→F−\mathrm{F} + e^- \rightarrow \mathrm{F}^-
  • Consequence: F−\mathrm{F}^- has the same electron count as Ne.