Lecture Notes: Ionic Bonds and Dot-and-Cross Diagrams

Introduction to Ionic Bonds

• Purpose: Understanding how particles bond through ionic bonds using dot-and-cross diagrams.

Recap of Ions

• Formation: Ions form when atoms lose or gain electrons.
  • Sodium Example: Sodium (Na) atom loses one electron to form Na⁺ ion.
    • Sodium has one electron in its outer shell, needs to lose it for stability (full outer shell).
  • Chlorine Example: Chlorine (Cl) atom gains an electron to form Cl⁻ ion.
    • Chlorine needs one more electron for a full outer shell.

Electron Transfer

• Real Life Reaction: Occurs through transfer of electrons, not in isolation.
  • Sodium transfers its extra electron to chlorine, forming Na⁺ and Cl⁻.
  • Resulting ions have opposite charges and attract each other via electrostatic forces.
  • This attraction forms an ionic bond.

Dot-and-Cross Diagrams

• Purpose: Visual representation of ionic bonds.

Features of Dot-and-Cross Diagrams

• Electron Representation:
  • Electrons from one atom shown as dots, other as crosses.
  • Movement of electrons indicated by arrows.
• Shells: Show all electron shells or only the outermost shell (as required).

Example: Drawing Dot-and-Cross Diagrams

Simple Example

• Sodium Chloride (NaCl):
  • Sodium loses one electron (dot) to chlorine (cross).
  • Na⁺ and Cl⁻ ions shown with full outer shells in brackets.

Complex Example

• Magnesium Chloride (MgCl₂):
  • Involves 3 atoms: Mg and two Cl.
  • Magnesium: Loses 2 electrons.
  • Chlorine: Each Cl gains 1 electron.
  • Arrangement: Chloride ions placed on either side of magnesium ion.

Conclusion

• Dot-and-cross diagrams aid in understanding ionic bonds.
• Essential for exams.
• Encouragement to share and review material.