Overview
This lesson explains ions—charged particles formed when atoms gain or lose electrons—and how their electronic structure relates to noble gases.
What Are Ions?
- Ions are atoms or molecules with an electric charge due to the loss or gain of electrons.
- Atoms become positively charged when they lose electrons, forming cations.
- Atoms become negatively charged when they gain electrons, forming anions.
- The charge of an ion is shown as a superscript by its symbol.
Formation of Ions: Examples
- Sodium (Na) has an electronic structure of 2,8,1 and loses one electron to form a Na⁺ cation.
- Oxygen (O) has an electronic structure of 2,6 and gains two electrons to form an O²⁻ anion.
- Both sodium and oxide ions have the same electronic structure as the noble gas neon.
Drawing Ion Structures
- Draw ions by showing full outer shells and indicating the charge in the top right using square brackets.
- Calcium (Ca) with electronic structure 2,8,8,2 loses two electrons to form Ca²⁺, matching argon’s structure.
- Chlorine (Cl) with electronic structure 2,8,7 gains one electron to form Cl⁻, also matching argon.
Patterns in Ion Formation Across the Periodic Table
- Metals (e.g., sodium, magnesium) lose electrons and form cations; group 1 forms +1 ions, group 2 forms +2 ions.
- Non-metals (e.g., oxygen, fluorine) gain electrons and form anions; group 6 forms -2 ions, group 7 forms -1 ions.
- Group 3 elements (e.g., aluminum) lose three electrons to form +3 ions.
- Group 5 elements (e.g., nitrogen) gain three electrons to form -3 ions.
- Group 4 elements (e.g., carbon) typically form covalent compounds instead of ions.
Key Terms & Definitions
- Ion — a charged atom or molecule, formed by gaining or losing electrons.
- Cation — a positively charged ion (atom loses electrons).
- Anion — a negatively charged ion (atom gains electrons).
- Valence electrons — electrons in the outermost shell of an atom.
- Noble gas structure — a stable, full outer electron shell, as seen in noble gases.
Action Items / Next Steps
- Practice drawing electronic structures of Ca²⁺ and Cl⁻ ions, including correct charge notation.
- Remember to specify charges and closed-shell configurations when representing ions.