Overview
This lecture covers the formation of ions, ionic bonds, and the properties of ionic compounds, with examples from group 1 and group 7 elements.
Ions and Their Formation
- An ion is an atom or group of atoms with a positive or negative charge.
- Atoms form ions to achieve a stable, full outer electron shell.
- Atoms become ions by losing (forming positive ions) or gaining electrons (forming negative ions).
- A cation is a positively charged ion formed by losing electrons (e.g., metals).
- An anion is a negatively charged ion formed by gaining electrons (e.g., non-metals).
- Example: Sodium (Na) loses one electron to form Na⁺ with a full outer shell.
- Example: Chlorine (Cl) gains one electron to form Cl⁻ with a full outer shell.
Ionic Bonds
- An ionic bond is a strong electrostatic attraction between oppositely charged ions.
- Ionic bonds typically form between metals (which lose electrons) and non-metals (which gain electrons).
- Example: Sodium donates its outer electron to chlorine, forming Na⁺ and Cl⁻.
- The resulting compound (e.g., sodium chloride, NaCl) consists of these ions.
Representation of Ionic Bonds
- Dot and cross diagrams represent how electrons are transferred in ionic bonds.
- Outer shell electrons are shown as dots (metals) or crosses (non-metals).
- Brackets indicate the charge and electron configuration of each ion.
Structure and Properties of Ionic Compounds
- Ionic compounds have a giant lattice structure: a regular arrangement of alternating positive and negative ions.
- They have high melting and boiling points due to strong ionic bonds.
- Ionic compounds conduct electricity when dissolved in water (aqueous) or molten but not when solid.
Key Terms & Definitions
- Ion — atom or group of atoms with an electric charge due to electron loss or gain.
- Cation — positively charged ion, formed by losing electrons.
- Anion — negatively charged ion, formed by gaining electrons.
- Ionic bond — strong electrostatic force between oppositely charged ions.
- Giant lattice structure — repeating 3D arrangement of ions in an ionic compound.
Action Items / Next Steps
- Review dot and cross diagrams for ionic bond formation.
- Practice writing electron configurations for common group 1 and group 7 ions.