diamond and silicon dioxide

• Giant covalent substances

  Contain millions of covalent bonds
• Giant covalent substances are always solids at room temperature
• Carbon atom

  • 4 electrons in outer energy level
  • Forms 4 covalent bonds to other carbon atoms
• Diamond

  Giant covalent substance formed from carbon atoms
• Representing diamond

  1. Carbon atoms shown as circles

  2. Covalent bonds shown as sticks
• Even a tiny diamond contains millions of carbon atoms joined by covalent bonds
• Diamond has a very high melting point (over 3,700 °C)
• Silicon dioxide (silica)

  Giant covalent substance containing silicon and oxygen atoms
• Silicon dioxide has a very high melting and boiling point