STRUCTURE AND UNIQUE PROPERTIES OF WATER

• Have you ever thought about why researchers keep looking for traces of water on other planets?
• This is mainly because water is essential to life. All life on earth depends on water.
• We, as humans, use water for drinking, cooking, cleaning and making other substances.
• If a planet has liquid water in it, then there is a chance that life, similar to Earth, may exist.
• In this lesson, you will learn about the unique properties of water that make it suitable for life.
• Water is represented by the chemical formula H2O.
• The Structure of Water

  • Lewis structure of water
  • There are 4 electron domains around the central atom, O
  • The electron domain geometry of water is tetrahedral
  • Since there are two lone pairs present, the molecular geometry becomes bent
  • Since oxygen is more electronegative than hydrogen, then the dipole moment moves towards the oxygen atom
  • The dipole moments do not cancel out. This means that the water molecule is polar
• Water has 4 electron domains around the central atom (O). It has two single bonds and two lone pairs. Its electron domain geometry is tetrahedral and its molecular geometry is bent.
• Intermolecular forces present in water

  • London dispersion forces
  • Dipole-dipole interactions
  • Hydrogen bonding
• Much of the unique properties of water are owed to the hydrogen bonding capacity of water.
• Physical Properties of Water

  • Specific heat capacity (liquid water): 4.18 J/g · ºC
  • Specific heat capacity (water vapor): 2.11 J/g · ºC
  • Specific heat capacity (ice): 2.00 J/g · ºC
  • Melting point: 0 ºC
  • Boiling point: 100 ºC
• Water has the highest boiling point due to H-bonds.
• This makes it more difficult to break the interactions between particles.
• Water as a Universal Solvent


  • Water is known to be the universal solvent due to its capacity to dissolve a wide variety of substances
  • Its ability to dissolve ionic solids stems from the polarity of the water molecule
  • When ionic compounds are dissolved in water, the ions break apart and each ion will be surrounded by water molecules, forming hydration sphere
• Water can dissolve ionic compounds through ion-dipole interactions.
• Water can dissolve polar compounds through dipole-dipole interactions.
• Amphiphatic molecules


  • Contain a polar and nonpolar regions
  • Fatty acids, such as palmitic acid, contain a long hydrophobic tail and a hydrophilic head
  • When placed in water it forms a micelle, which is an assembly of fatty acids, wherein the hydrophobic tails are hidden inside the structure and the hydrophilic heads are exposed
• Heat Capacity


  • Heat capacity is the amount of heat required to raise the temperature of a substance by 1 ºC
  • Specific heat capacity refers to the amount of heat required to raise the temperature of one gram of a substance by 1 ºC
  • For liquid water, the specific heat capacity is 4.18 (J/g × ºC)
• Specific heat capacity of various substances

  • Liquid water: 4.18 J/g × ºC
  • Water vapor: 2.11 J/g × ºC
  • Ice: 2.00 J/g × ºC
  • Dry air: 1.01 J/g × ºC
  • Magnesium: 1.024 J/g × ºC
  • Aluminum: 0.903 J/g × ºC
  • Iron: 0.449 J/g × ºC
  • Zinc: 0.389 J/g × ºC
  • Copper: 0.385 J/g × ºC
  • Granite: 0.79 J/g × ºC
• Remember that from the kinetic molecular theory, temperature is defined as the measure of the average kinetic energy of the particles.
• When the particles move faster, this translates to a higher temperature.
• The hydrogen bonds are able to absorb the energy in the form of heat.
• Heat capacity is an extensive property while specific heat is an intensive property.
• Phases of Water


  • Water, like all matter, can exist as a solid (ice), liquid (water), or gas (steam)
  • From the kinetic molecular theory, solids typically have a more compact arrangement of particles than liquids and gases
  • However, this is not true for water
  • When liquid water solidifies to ice, it arranges itself based on the hydrogen bonding requirements
  • When a hydrogen bond is formed the hydrogen donor-hydrogen acceptor-hydrogen atom bond should be 180 degrees

  
• It is the type of covalent compound that applies to water.
• It is the molecular geometry of water.
• It is the amount of heat needed to increase the temperature of a gram of a substance by one degree Celsius.
• Brown T.L. et al. 2012. Chemistry: The Central Science. Pearson Prentice Hall.
• Bettelheim, Frederick A., et al. 2015. Introduction to General, Organic and Biochemistry. Boston: Cengage Learning.
• Ebbing, Darrell and Steven Gammon. 2016. General Chemistry. Boston: Cengage Learning.
• Moore, John W, and Conrad L. Stanitski. 2015. Chemistry: The Molecular Science, 5th ed. USA: Cengage Learning.
• Petrucci, Ralph H. General Chemistry: Principles and Modern Applications. Toronto, Ont.: Pearson Canada, 2011. Print.