Properties of substances with small molecules

• What is a covalent bond?

  A covalent bond is a shared pair of electrons.
• What do covalent bonds form?

  Covalent bonds form molecules.
• What are the melting and boiling points of substances with small molecules?

  They have low melting and boiling points.
• Do substances with small molecules conduct electricity?

  No, they do not conduct electricity.
• What are the properties of substances with small molecules?

  • Strong covalent bonds within molecules
  • Weak forces between molecules
  • Low melting and boiling points
  • Often exist as liquids or gases at room temperature
• What is the definition of a molecule?

  A molecule is a collection of two or more atoms held together by chemical bonds.
• What happens to the attractive forces during melting and boiling?

  Some forces of attraction are overcome during melting, and more are overcome during boiling.
• What is the temperature at which a solid changes into a liquid called?

  The melting point.
• What is the temperature at which a substance rapidly changes from a liquid to a gas called?

  The boiling point.
• What must be transferred to a substance to make it melt or boil?

  Energy must be transferred to the substance.
• What are intermolecular forces?

  Intermolecular forces are weak attractive forces between molecules.
• What happens when a simple molecular substance melts or boils?

  The weak intermolecular forces are broken, not the covalent bonds in each molecule.
• Why do small molecular substances have low melting and boiling points?

  Relatively little energy is needed to overcome the intermolecular forces.
• What is the melting point of O₂?

  • 218°C
• What is the boiling point of H₂O?

  100°C
• What state is O₂ at 20°C?

  Gas
• What state is H₂O at 20°C?

  Liquid
• How do the intermolecular forces between water molecules compare to those between oxygen molecules?

  The intermolecular forces between water molecules are stronger than those between oxygen molecules.
• How does the size of a molecule affect its intermolecular forces?

  The bigger the molecule, the stronger the intermolecular forces.
• What is required for a substance to conduct electricity?

  A substance must contain charged particles that are free to move.
• Why can't small molecules conduct electricity?

  Small molecules have no overall electric charge.
• What is a key fact about simple molecular substances when they melt or boil?

  • Their weak intermolecular forces are overcome
  • Their strong covalent bonds remain intact