Water

The chemical reactions of all living things take place in an aqueous (water based) environment. Thus, water is one of the most important compounds found in living things.

A. Water: the single most abundant compound in most living things

B. Chemical formula: H20 (2 part hydrogen, 1 part oxygen)

C. Bohr model for water (covalent bonds)

D. Water is a polar covalent compound

  1. Polar: the electrons are unevenly shared between the hydrogen and oxygen atoms.

  2. Oxygen pulls on the e- greater than the H so at any moment, the shared e- are more likely closer to the oxygen.

  3. What effect does “polar” have

    • water has a partial positive pole and partial negative pole

    • like a magnet

E. Hydrogen bonding

  1. the partial positive and partial negative charges allow H20 molecules to attract to each other or stick together through hydrogen bonds

  2. Hydrogen bonds are weak bonds that can be broken

  3. H-bonds are responsible for waters specials properties

    Polar covalent bonds are within the compound and hydrogen bands are between other water molecules.

F. Properties of water

  1. Strong cohesion and adhesion forces

    • Cohesion = attraction between molecules of the same substance

    • Ex. cohesion leads to water having a high surface tension due to the hydrogen bonding of surface molecules to each other

    • Adhesion = attraction between molecules of different substances

    • Capillary action = the movement of water within spaces of a porous material due to the forces of adhesion, cohesion, and surface tensio

    • Surface tensions = The slightly elastic quality along the surface of water allows certain insects to walk on water.

  2. Waters high specific heat capacity

    • Water can absorb heat and large amounts of thermal energy before its own

    • Water acts like a heat buffer for the globe

    • Heat capacity: it is caused by hydrogen bonding among water molecules, when heat is absorbed, hydrogen bonds are broken, and water molecules can move freely

  3. Ice

    • ice is less dense than liquid water

  4. Ability to form solutions

    • water is very effective in dissolving many other substances

  5. Water is the universal solvent

    • Solution: liquid consisting of uniform mixture of two or more substances (Kool-Aid)

    • Solvent: Liquid (dissolving agent) (ex. water)

    • Solute: substance dissolved (ex. Kool-Aid powder/sugar)

G. Remember the rule to make a solution

  • Since water is polar, it will dissolve ions and other polar substances

  • Hydrophilic = water lover

  • Water will NOT dissolve non-polar substances