Properties of small covalent molecules

• Small covalent molecules


  Molecules with a small number of atoms, e.g. methane with 5 atoms
• Small covalent molecules


  • Have low melting and boiling points
  • Are usually gases or liquids at room temperature
• Small covalent molecules


  • Methane
  • Other molecules shown
• Water is a liquid at room temperature, but has a relatively low boiling point of 100°C
• Why small covalent molecules have low melting and boiling points

  1. Atoms in each molecule held together by strong covalent bonds

  2. Weak intermolecular forces between molecules

  3. As temperature increases, vibration of molecules increases

  4. At a certain point, vibration is strong enough to break weak intermolecular forces, causing the substance to boil
• Covalent bonds are not broken when a substance melts or boils
• As the size of the covalent molecule increases

  The intermolecular forces increase, requiring more energy to break them and increasing the boiling point
• Intermolecular forces


  Weak forces between one molecule and another molecule
• Small covalent molecules do not conduct electricity
• Small covalent molecules do not have an overall electric charge