Free Science Lessons: Giant Covalent Molecules

Introduction

• Focus of the video:
  • Describe the structure of giant covalent molecules: Diamond and Silicon Dioxide
  • Discuss properties of these molecules
  • Link properties to the structures
• Previous video: Properties of small covalent molecules (link in description)

Small Covalent Molecules Recap

• Example: Hydrogen molecule (H2)
• Characteristics:
  • Small number of covalent bonds
  • Weak intermolecular forces between molecules
  • Low melting and boiling points
  • Mostly gases at room temperature

Giant Covalent Substances

• Differ from small covalent substances:
  • Contain millions of covalent bonds
• Examples discussed:
  • Diamond
  • Silicon Dioxide
  • (Graphite discussed in next video)
• Key fact:
  • Always solid at room temperature
  • High melting and boiling points due to many strong covalent bonds

Diamond

• Formed from carbon
  • Carbon atoms have four electrons in outer energy level
  • Each carbon atom forms covalent bonds with four other carbon atoms
• Structure:
  • Millions of carbon atoms bonded by covalent bonds
  • Represented with atoms as circles and bonds as sticks in diagrams
• Properties:
  • Extremely hard
  • Very high melting point (> 3,700°C)
  • Does not conduct electricity
    • All outer electrons are in covalent bonds
    • No free electrons to carry charge

Silicon Dioxide (Silica)

• Contains silicon and oxygen, covalently bonded
• Giant covalent molecule:
  • Huge number of covalent bonds
• Properties:
  • Very high melting and boiling point
  • Strong covalent bonds require a lot of energy to break

Conclusion

• Topic questions available in vision workbook (link available in video)