diamond and silicon dioxide

• What distinguishes small covalent molecules from giant covalent substances?

  Giant substances have millions of covalent bonds
• What are the three giant covalent substances mentioned?

  Diamond, silicon dioxide, and graphite
• Why are giant covalent substances always solids at room temperature?

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

  They require breaking millions of strong covalent bonds
• What element is diamond formed from?

  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 the diagram of diamond represent?

  Carbon atoms as circles and covalent bonds as sticks
• What makes diamond an extremely hard substance?

  Millions of carbon atoms joined by covalent bonds
• What is the melting point of diamond?

  Over $3,700 \text{ °C}$
• Why can't diamond conduct electricity?

  All outer electrons are in covalent bonds
• 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?

  It has a huge number of strong covalent bonds