Diamond and Silicon Dioxide

• What are the two giant covalent substances discussed in this video?

  Diamond and silicon dioxide
• What are the characteristics of giant covalent substances?

  • Always solids at room temperature
  • High melting and boiling points
  • Contain millions of covalent bonds
• Why do giant covalent substances have high melting and boiling points?

  Because they have millions of strong covalent bonds that require a lot of energy to break.
• What type of intermolecular forces exist in small covalent substances?

  Weak intermolecular forces
• How do the melting and boiling points of small covalent substances compare to those of giant covalent substances?

  Small covalent substances have low melting and boiling points, while giant covalent substances have high melting and boiling points.
• What are the properties of diamond as a giant covalent substance?

  • Extremely hard
  • Very high melting point (over 3,700 °C)
  • Cannot conduct electricity
• What element is diamond formed from?

  Carbon
• Why can't diamond conduct electricity?

  Because all outer electrons are in covalent bonds, leaving no free electrons to conduct electricity.
• What is silicon dioxide and what elements does it contain?

  • Silicon dioxide is a giant covalent molecule
  • Contains silicon and oxygen covalently bonded together
• How does the melting point of silicon dioxide compare to that of diamond?

  Both have very high melting points due to strong covalent bonds.
• What must be broken to melt silicon dioxide?

  Covalent bonds
• Why does melting silicon dioxide require a great deal of energy?

  Because it requires breaking a huge number of strong covalent bonds.