Water

 In a water molecule two hydrogen atoms form single polar covalent bonds with an oxygen atom. Gives water more structure than other liquids ◦ Because oxygen is more electronegative, the region around oxygen has a partial negative charge. ◦ The region near the two hydrogen atoms has a partial positive charge.  A water molecule is a polar molecule with opposite ends of the molecule with opposite charges.

 Water has a variety of unusual properties because of attractions between these polar molecules. ◦ The slightly negative regions of one molecule are attracted to the slightly positive regions of nearby molecules, forming a hydrogen bond. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 3.1

 Hold water molecules together  Each water molecule can form a maximum of 4 hydrogen bonds  The hydrogen bonds joining water molecules are weak, about 1/20 th as strong as covalent bonds.  They form, break, and reform with great frequency  Extraordinary Properties that are a result of hydrogen bonds. ◦ Cohesive behavior ◦ Resists changes in temperature ◦ High heat of vaporization ◦ Expands when it freezes ◦ Versatile solvent

Cohesion/Adhesion (surface tension)  Capillarity (Capillary Action)  High Specific Heat  Density  Salinity  Solvent (universal)  Transparent

 Cohesion is responsible for the transport of the water column in plants  Cohesion among water molecules plays a key role in the transport of water against gravity in plants  Adhesion- clinging of one substance to another-contributes too as water adheres to the wall of the vessels. Hydrogen bonds hold the substance together, a phenomenon called cohesion

 Surface tension, a measure of the force necessary to stretch or break the surface of a liquid, is related to cohesion. ◦ Water has a greater surface tension than most other liquids because hydrogen bonds among surface water molecules resist stretching or breaking the surface. ◦ Water behaves as if covered by an invisible film. ◦ Some animals can stand, walk, or run on water without breaking the surface. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 3.3

The movement of a liquid along the surface of a solid caused by the attraction of molecules of the liquid to the molecules of the solid. water evaporates from leaves = transpiration adhesion, cohesion and capillary action All thanks to hydrogen bonding! water taken up by roots

trees have specialized structures to transport water: xylem and phloem “plumbing” water molecules are “dragged” from the roots to the top of the tree by capillary action and cohesion: hydrogen bonds help water molecules to each other

Three-fourths of the earth is covered by water. The water serves as a large heat sink responsible for: 1.Prevention of temperature fluctuations that are outside the range suitable for life. 2.Coastal areas having a mild climate 3.A stable marine environment

Celsius Scale at Sea Level 100 o CWater boils 37 o CHuman body temperature 23 o CRoom temperature 0oC0oCWater freezes Water stabilizes air temperatures by absorbing heat from warmer air and releasing heat to cooler air. Water can absorb or release relatively large amounts of heat with only a slight change in its own temperature.

◦ Heat of vaporization  Amount of energy required to change 1g of liquid water into a gas (586 calories).  large number of hydrogen bonds broken when heat energy is applied

 As a liquid evaporates, the surface of the liquid that remains behind cools - Evaporative cooling.  Evaporative cooling moderates temperature in lakes and ponds and prevents terrestrial organisms from overheating.  Evaporation of water from the leaves of plants or the skin of animals removes excess heat.

The relationship between temperature, salinity and density of seawater-as temperature increases, salinity and density increase

 Most dense at 4 o C  Contracts until 4 o C  Expands from 4 o C to 0 o C The density of water: 1.Prevents water from freezing from the bottom up. 2.Ice forms on the surface first—the freezing of the water releases heat to the water below creating insulation. 3.Makes transition between season less abrupt.

◦ When water reaches 0 o C, water becomes locked into a crystalline lattice with each molecule bonded to the maximum of four partners. ◦ Ice is about 10% less dense than water at 4 o C. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 3.5

 A liquid that is a completely homogeneous mixture of two or more substances is called a solution.  The solvent is the material doing the dissolving and in sea water it is the water.  The solute is the material being dissolved. 5-3

 Water is often referred to as the universal solvent  In an aqueous solution, water is the solvent.  Water is not really a universal solvent, but it is very versatile because of the polarity of water molecules.

 Salinity is the total amount of salts dissolved in the water.  It is measured in parts of salt per thousand parts of salt water and is expressed as ppt (parts per thousand) or abbreviated ‰.  Average salinity of the ocean is about 35‰.  The salinity of ocean water slightly LOWERS its freezing point and makes it MORE DENSE than freshwater

 The fact that water is clear allows light to pass through it ◦ Aquatic plants can receive sunlight ◦ Light can pass through the eyeball to receptor cells in the back

 Occasionally, a hydrogen atom shared by two water molecules shifts from one molecule to the other. ◦ The hydrogen atom leaves its electron behind and is transferred as a single proton - a hydrogen ion (H + ) (ACIDIC). ◦ The water molecule that lost a proton is now a hydroxide ion (OH - )(BASIC). ◦ The water molecule with the extra proton is a hydronium ion (H 3 O + ). Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Unnumbered Fig. 3.47

 An acid is a substance that increases the hydrogen ion concentration in a solution.  Any substance that reduces the hydrogen ion concentration in a solution is a base. ◦ Some bases reduce H + directly by accepting hydrogen ions.  Strong acids and bases complete dissociate in water.  Weak acids and bases dissociate only partially and reversibly.

 Measures the power of Hydrogen ion (degree of acidity from 0 – 14)  ACID- pH ranges from pH  NEUTRAL 7  BASE- pH ranges from pH 7.1 – 14  Most biologic fluids are in the pH range from 6 – 8  Each pH unit represents a tenfold difference (scale is logarithmic) (10x bigger or smaller) ◦ A small change in pH actually indicates a substantial change in H + and OH - concentrations.

 A substance that eliminates large sudden changes in pH.  Buffers help organisms maintain the pH of body fluids within the narrow range necessary for life. ◦ Example: Bicarbonate and Phosphate buffers in blood help keep pH around 7.4

 Rain, snow or fog with more strongly acidic than pH of 5.6  West Virginia has recorded 1.5  Occurs when sulfur oxides and nitrogen oxides react with water in the atmosphere ◦ Lowers pH of soil which affects mineral solubility – decline of forests ◦ Lower pH of lakes and ponds – In the Western Adirondack Mountains, there are lakes with a pH <5 that have no fish.