Diamond and Silicon

• What distinguishes small covalent molecules from giant covalent substances?

  Giant substances have millions of covalent bonds
• Why do small covalent substances have low melting and boiling points?

  They have weak intermolecular forces
• What happens when we melt or boil a small covalent substance?

  We break weak intermolecular forces
• What are giant covalent substances always at room temperature?

  Solids
• Why do giant covalent substances have high melting and boiling points?

  They have millions of strong covalent bonds
• What is diamond formed from?

  The element carbon
• How many electrons are in the outer energy level of a carbon atom?

  Four electrons
• How does a carbon atom achieve a full outer energy level?

  By forming covalent bonds with four other carbon atoms
• What does a diagram of diamond represent?

  Carbon atoms as circles and covalent bonds as sticks
• Why is diamond considered an extremely hard substance?

  It contains millions of carbon atoms joined by covalent bonds
• What is the melting point of diamond?

  Over 3,700 °C
• Why can't diamond conduct electricity?

  It has no free electrons to carry charge
• What is silicon dioxide also known as?

  Silica
• What elements are covalently bonded in silicon dioxide?

  Silicon and oxygen
• How does silicon dioxide compare to diamond in terms of melting and boiling points?

  Both have very high melting and boiling points
• Why does melting silicon dioxide require a great deal of energy?

  Because strong covalent bonds must be broken
• What are the properties of giant covalent substances?

  • Always solids at room temperature
  • High melting and boiling points
  • Millions of strong covalent bonds
• What are the differences between small covalent molecules and giant covalent substances?

  Small covalent molecules:

  • Few covalent bonds
  • Weak intermolecular forces
  • Low melting and boiling points

  
  

  Giant covalent substances:

  • Millions of covalent bonds
  • Strong covalent bonds
  • High melting and boiling points