Forces and Properties of Substances

• INTRAMOLECULAR FORCES - Forces that hold atoms together within a molecule.
• Atom - smallest unit of matter
• Molecule - group of two or more atoms held together by forces known as chemical bonds.
• INTERMOLECULAR FORCE - Attractive and repulsive forces that hold molecules together in substance.
• FOUR (4) MAIN TYPES OF INTERMOLECULAR FORCES 1. Ion-Ion Forces

  2. Dipole-Dipole Forces

  *2.1 Hydrogen Bonds

  3. Dispersion Forces
• 1. ION-ION FORCES - Occurs between ionic compounds. - Exist between oppositely charged ions. - Strength of attraction: HIGH
• 2. DIPOLE-DIPOLE FORCES - Occurs between polar molecules. - Strength of attraction: MEDIUM - Average dipole-dipole interaction is relatively weak and thus, effective over a very short range.
• 3. HYDROGEN BONDS - Special forces dipole-dipole - Occurs between polar molecules containing H and any one of the highly electronegative elements (F, O, N). - Strength of attraction: MEDIUM-HIGH
• 4. DISPERSION FORCES - "London Forces" - Present in ALL molecules. - Occurs between nonpolar molecules. - Strength of attraction: LOW
• Five (5) Properties of Substances 1. Boiling and Melting Point 2. Capillary Action 3. Evaporation or Vaporization 4. Surface Tension 5. Viscosity
• BOILING POINT - The temperature at which liquid turns into gas.
• MELTING POINT - The temperature at which solid turns into liquid.
• CAPILLARY ACTION - "Capillarity" - Ability of a liquid to pass through a narrow space without the assistance or opposition of external forces.
• EVAPORATION - "Vaporization" - The heat required to turn liquid to gas.
• SURFACE TENSION - An effect that causes the surface layer of a liquid to behave as an elastic sheet.
• VISCOSITY - The ability of a liquid to resist flowing.
• The stronger the forces between particles, the higher its property.