Overview
This lecture covers ionic compounds, focusing on their structure, properties, and how to determine their chemical formulas.
Structure of Ionic Compounds
- Ionic bonding occurs when a metal atom transfers electrons to a non-metal atom, forming oppositely charged ions.
- The ions are held together by electrostatic forces, creating an ionic bond.
- Ionic compounds are made of many alternating positive and negative ions in a regular three-dimensional lattice structure.
- Ball and stick diagrams can represent ionic compounds, showing ions and the bonds between them.
Properties of Ionic Compounds
- Ionic compounds have high melting and boiling points due to strong ionic bonds that require a lot of energy to break.
- They conduct electricity only when melted or dissolved in water because ions are free to move in those states.
- In solid form, ionic compounds do not conduct electricity since ions are fixed in place.
Determining Formulas of Ionic Compounds
- The formula of an ionic compound balances the total positive and negative charges to make the compound neutral.
- Sodium chloride: Na⁺ and Cl⁻ combine in a 1:1 ratio, formula is NaCl.
- Magnesium chloride: Mg²⁺ needs two Cl⁻ to balance, formula is MgCl₂.
- For polyatomic ions like hydroxide (OH⁻) and sulfate (SO₄²⁻), memorize their formulas and charges.
- Calcium hydroxide: Ca²⁺ combines with two OH⁻ ions, formula is Ca(OH)₂ (brackets show two whole hydroxide ions).
- Aluminium sulfate: Al³⁺ and SO₄²⁻ balance by using two Al³⁺ and three SO₄²⁻, formula is Al₂(SO₄)₃.
Key Terms & Definitions
- Ionic Bond — Attraction between oppositely charged ions.
- Lattice Structure — A regular, repeating arrangement of ions in all directions.
- Polyatomic Ion — An ion made of multiple atoms (e.g., OH⁻, SO₄²⁻).
- Formula — The symbolic representation showing the ratio of ions in a compound.
Action Items / Next Steps
- Memorize the formulas and charges for common polyatomic ions: OH⁻, SO₄²⁻, NO₃⁻, CO₃²⁻, NH₄⁺.