Properties of solids and liquids

• Physical Properties of Liquid Affected by IMF

  • Boiling Point and Melting Point
  • Viscosity
  • Surface Tension
  • Adhesion and Cohesion-Capillary
  • Vapor Pressure
• IMF like van der Waals forces consists of dipole interactions and dispersion forces
• Dispersion forces are said to be the weakest of all IM forces
• The relatively strong attraction found in hydrogen-containing molecules and water is called hydrogen bond which is stronger than dipole-dipole interactions
• IMF is generally weaker than ionic or covalent bonds between atoms in a molecule
• When comparing different substances, their IMF strength can be identified by

  • Identifying the type of intermolecular forces of attraction
  • Considering the polarity of the molecules
  • Comparing their molecular masses
• The strength of the IMF increases with increasing molecular masses
• Liquids have a definite volume due to the intermolecular forces of attractions between liquid molecules
• When the molecule is polar, it suggests stronger IMF but it is not always true
• Physical properties of liquid

  • Boiling Point and Melting Point
  • Viscosity
  • Surface Tension
  • Adhesion and Cohesion-Capillary
  • Vapor Pressure
• Boiling occurs when the pressure exerted by escaping molecules of the liquid and the molecules in the atmosphere are in equilibrium
• The normal boiling point of a liquid is at 1.0 atmosphere or 760 mm Hg
• Boiling


  Occurs when the pressure exerted by escaping molecules of the liquid and the molecules in the atmosphere are in equilibrium
• Boiling points of substances in order of increase: N2 < Cl2 < ClNO < CCl4
• Viscosity is the resistance to flow. Compounds with high or strong IMF are more viscous than compounds with weak IMF. Viscosity increases with increasing molar mass and decreases with increasing temperature
• Boiling point and melting point of liquids are directly proportional to their IMF strength and molecular masses
• Surface tension is the energy required to increase the surface area of a liquid by a unit amount depending on the nature of the liquid’s intermolecular forces of attraction
• Substances that reduce the surface tension of the liquid and allow it to spread more easily are called wetting agents
• Adhesive forces refer to the attraction between different substances, while cohesive forces refer to the attraction between similar substances
• Cohesion attributes to the surface tension of liquids
• Macroscopic effects of cohesion and adhesion: polar substances like water have partial positive and negative charges that attract neighboring molecules
• Cohesion and adhesion


  1. Partial positive charge on hydrogen atoms and partial negative charge on the oxygen in a polar substance like water

  2. Partial negatively charged molecule of water attracted to neighboring partial positively charged molecule of water forming a cohesive force of attraction between water molecules

  3. Water molecules in the container pulled and pushed evenly in all directions producing a zero net pull and push

  4. Water molecules on the surface experience a net downward pull due to lack of pulling forces in the upward direction

  5. Adhesive force of attraction between water molecules and the surface of the wall of the graduated cylinder causes the formation of the curvature of the liquid’s surface or the meniscus
• Surface tension


  • Depends on cohesive forces and adhesive forces between molecules
  • Decreases with increasing cohesive forces compared to adhesive forces
• Capillary Action is the rising of the liquid inside a capillary or slim tube or permeable substance due to adhesion and cohesion
• Surface tension occurs as a result of cohesive forces between the molecules of the liquid
• Capillary action increases with decreased surface tension
• Vapor pressure is the partial pressure of the substance in vapor phase present above the liquid sample in a closed container
• Different substances have different vapor pressures at a given temperature due to varying intermolecular forces
• Molecules need enough kinetic energy to escape into the vapor phase by breaking the intermolecular forces at the surface of the liquid
• Liquids with high vapor pressure at room temperature are volatile
• The volatility of the liquid is determined primarily by the IMF
• Volatility


  The more volatile the liquid is, the higher the vapor pressure (determined by the strength of IMF)
• Vapor pressure depends largely on the particular liquid and the temperature
• Vapor pressure does not depend on the amount of liquid nor the amount of vapor pressure
• The weaker the IMF, the more volatile the liquid is (the vapor pressure is high)
• Surface tension of liquids depends on the two intermolecular forces of attraction, cohesive forces, and adhesive forces
• Capillary action occurs only when the adhesive forces are strong
• The solid form of most substances is usually denser than the liquid state due to stronger intermolecular forces of attraction
• Most solid substances will sink when dropped in a liquid or body of water
• Authors: 'Brown, T.L., LeMay, H.E., Bursten, B.E., Murphy, C.J., and Woodward, P.M. (2012)'