 Most important inorganic molecule in living things.  Living organisms = 75-80% H 2 O.  Many biological processes require H 2 O › Survive days without food › Survive 3 days without water

 Solid (ice)  Liquid  Gas (vapor)

 Buoyancy  Polarity  Cohesion  Adhesion  Surface Tension  High Specific Heat  Forms solutions  Neutral pH

 High Specific Heat- a lot of heat is needed to raise the temperature of 1 gram of H 2 O by 1°C  H 2 O retains heat & cools slowly. › Ex: pool/ocean is warm in the fall.  Allows organisms to maintain relatively constant body temperatures.

 Atoms of different elements don’t always share e- equally. › More protons (+) in the nucleus means a stronger attraction for electrons (-).

 e- drawn the nucleus with more protons MORE than the others. › Charges form  polar molecules or polar regions of large molecules

 Cohesion - ability of H 2 O molecules to resist coming apart. › Keeps H 2 O molecules together as they move from roots to leaves. Giant Sequoia

 How droplets of H 2 O form.  Attraction between H 2 O molecules  surface tension › Surface Tension - molecules in the surface layer are H-bonded to H 2 O molecules below them. › Prevents water’s surface from easily breaking. Water StriderDroplet Formation

 Adhesion - attraction between H 2 O molecules and molecules of other substances (that can form H-Bonds). › Due to polarity of H 2 O › Other polar substances get wet (mix with H 2 O) › Nonpolar molecules, like oils, do not.

 Attraction of H 2 O to surfaces with a charge  capillary action  Capillary Action- tendency of liquids to rise in tubes of small diameter. › Explains movement of H 2 O from roots  leaves

 Many substances dissolve in H 2 O.  Solution - mixture in which 1+ substances are evenly distributed in another substance. › Can be mixtures of liquids, solids, or gases. › Substances transported in organisms as solutions of water.  Ex: Plasma (liquid part of blood)- made up of various ions and macromolecules, as well as gases, that are dissolved in H 2 O.

 Solute - substance being dissolved. › Ex: Sugar  Solvent - substance in which solute is dissolved. › Ex: H 2 O Sugar + H 2 O  Sugar H 2 O **Sugar & H 2 O molecules remain unchanged and can be separated again.**

 Ice (solid) is LESS dense than liquid H 2 O.

 Bonds break between some water molecules as they collide. › Forms a H ion (H+) and a hydroxide ion (OH-).  Pure H 2 O ALWAYS has a low concentration of H+ and OH- ions  H+ ions = OH- ions

 Compounds that form H+ when dissolved in H 2 O are acids. › Adding acids to pure H 2 O  H+ level increases above that of pure H 2 O  Bases - compounds that reduce [H+] in a solution. › Many bases form OH- when dissolved in H 2 O. › Lower [H+] because OH- reacts with H+ to form H 2 O.

 pH scale- measures H+ concentration in a solution.

 Each whole # (on pH scale) represents a factor of 10. › Solution with pH 5 has 10 times more H+ than a solution with pH 6. › Note: Stomach acid pH= 2 Blood pH= 7.5

1. Lemons have a pH of 2. Are lemons acidic or basic? 2. The strongest bases have a pH of ____. 3. Pure water is a neutral substance. What is the pH of pure water?

 Matter:  Matter Video Review: nano_vid_matter/ nano_vid_matter/  Atomic Structure:  Chemical Bonding:  Water Video:  NOVA Hunting the Elements Video: