Chemistry

• All life on earth depends on water
• 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
• Structure of water


  • 4 electron domains around the central atom, O
  • Tetrahedral electron domain geometry
  • Bent molecular geometry
  • Dipole moment moves towards the oxygen atom
  • Polar molecule
• 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
• Polarity of water


  Much of the unique properties of water are owed to the hydrogen bonding capacity of water
• Properties of water


  • Polar
  • Universal solvent
  • High heat capacity
  • High heat of vaporization
  • Cohesive and adhesive properties
  • Less dense as a solid than as a liquid
• Water as a universal solvent


  • Its ability to dissolve ionic solids stems from the polarity of the water molecule
  • Ions break apart and each ion will be surrounded by water molecules, forming hydration sphere
  • Water can dissolve ionic compounds through ion-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


  • 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 substances


  • liquid water: 4.18 J/g × ºC
  • water vapor: 2.11 J/g × ºC
  • ice: 2.00 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
• Heat capacity


  • Temperature is 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
• High heat of vaporization of water

  • Humans (and other animals that sweat) use water's high heat of vaporization to cool off
  • Water is converted from its liquid form to steam when the heat of vaporization is reached
  • Sweat is made mostly of water, the evaporating water absorbs excess body heat, which is released into the atmosphere. This is known as evaporative cooling
• Cohesive and adhesive properties of water

  • Water molecules have strong cohesive forces due to their ability to form hydrogen bonds with one another
  • Cohesive forces are responsible for surface tension, the tendency of a liquid's surface to resist rupture when placed under tension or stress
  • Water also has adhesive properties that allow it to stick to substances other than itself
  • These cohesive and adhesive properties are essential for fluid transport in many forms of life
• Water is less dense as a solid than as a liquid


  • As water freezes, the molecules form a crystalline structure that spaces the molecules further apart than in liquid water
  • This means that ice is less dense than liquid water, which is why it floats
• 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
• Intermolecular forces present in water


  • London dispersion forces
  • Dipole-dipole interactions
  • Hydrogen bonding
• Water is the universal solvent since it can dissolve a wide variety of solutes
• The water's high boiling point and heat capacity are both due to the strong hydrogen bonds present in water molecules
• Liquid water is more dense than ice due to the geometrical and spatial restrictions of the hydrogen bonds
• How can you relate the properties of water to its important role in maintaining life