2.1 Ionic Compounds

Ionic Compounds

• Scientists estimate over 10 million different compounds exist, with more being created daily.

• Compounds in households vary greatly; some are safe to consume, while others, like ammonia, are toxic.

Comparison of Ionic and Molecular Compounds

• Types of Compounds:

  • Ionic Compounds: Composed of a metal and a non-metal.

  • Molecular Compounds: Comprised of two or more non-metallic elements.

• Chemical bonds act as invisible "glue" holding atoms together and influence the properties of compounds.

Properties of Ionic Compounds

• Common examples: NaCl (table salt), CaCO3 (limestone), HgS (cinnabar).

• Structure: Composed of metallic and non-metallic elements.

• Properties:

  • Hard and brittle

  • High melting (e.g., NaCl ~801 °C) and boiling points.

  • Conduct electricity when molten or dissolved in water (e.g., NaCl is an electrolyte).

• Electrolytes: Compounds that dissolve in water to form conductive solutions, crucial for bodily functions (e.g., sports drinks replenish lost electrolytes).

Formation of Ionic Compounds

• Example: Sodium chloride (NaCl) forms by the transfer of electrons, converting neutral sodium (Na) into a cation (Na+) and chlorine (Cl) into an anion (Cl-).

• General Process:

  • Metals (like sodium) lose electrons to form cations.

  • Non-metals (like chlorine) gain electrons to form anions.

• Electrostatic forces attract the oppositely charged ions, resulting in ionic bonds.

Common Properties of Ionic Compounds

• Shared Characteristics:

  • Solid at room temperature

  • Definite geometries (often cubic)

  • High melting and boiling points due to strong electrostatic forces.

• Electrical Conductivity: Not conductive as solids but conductive when melted or dissolved in water, as shown with NaCl.

Structure of Ionic Compounds

• Large assemblies of positive (cations) and negative (anions) ions make up a crystal lattice structure.

• The formula unit defines the smallest repeating unit in an ionic crystal (e.g., NaCl, HgS).

Explaining Properties via Structure

• High Melting Points: Strong ionic bonds among ions increase melting points.

• Hardness: Resilience to stretching due to the strong bonds.

• Brittleness: Displacement causes like-charged ions to repel, leading to breaks.

• Dissolution in Water: Water molecules surround and separate the ions, allowing conductivity.

Summary

• Two primary types of chemical compounds exist: ionic and molecular.

• Ionic compounds consist of cations and anions linked by ionic bonds.

• Their distinguishable properties result from ionic bonds, affecting their melting points, hardness, and conductivity.

• Lewis symbols: A tool to represent the formation of ionic bonds.

Questions

1. Distinctive Properties of Ionic Compounds:

   • Hardness

   • High melting and boiling points

   • Conductivity when dissolved or molten.

2. Definitions:

   • Electrolyte: Compound producing an electric conducting solution when dissolved in water.

   • Ionic bond: The electrostatic attraction between cations and anions.

   • Formula unit: The smallest repeating unit in an ionic compound.

3. Lewis Symbols: Represent formation of bonds in magnesium oxide; Example:

   • Mg + O → MgO

4. Conductivity Difference: Tap water contains ions from minerals, allowing better conductivity than pure water.

5. Ionic Bond Strength Comparison: Based on melting points; stronger ionic bonds show higher melting points due to electrostatic interaction strength.

6. Support for Ionic Bonding Theory: Hardness shows resistance to deformation; brittleness shows prone to break due to similar ions repelling each other.

7. Lewis Symbols Practice:

   • Draw Lewis symbols for compounds like lithium chloride, magnesium chloride, sodium sulfide, aluminum oxide.

8. Element Classification: Determine if Element A (2 valence electrons) is a metal and Element B (7 valence electrons) a non-metal.

9. Research Connections: Explore similarities between ionic compounds and fabrics/patterns.

10. Road Salt Research: Look into the effects of sodium and calcium chloride on roads and environmental impacts.