Understanding Water

STRUCTURE OF WATER MOLECULE Hydrogen atom Hydrogen atom Formula: H2O Oxygen atom

H+ H+ O- POLARITY OF WATER Different sides of molecule have different charges. Due to unequal sharing of electrons. H+ H+ O- Oxygen side is negative because it has a stronger attraction of electrons.

COVALENT BONDING Sharing of electrons between atoms Sharing electrons Sharing of electrons between atoms Oxygen has 6 valence electrons Hydrogen has 1 valence electron H H O

Cohesion Water molecules stick to each other. Creates surface tension Positive side attracted to negative side Creates surface tension Water is pulled easily through small vessels (capillary action)

Adhesion Water molecules stick to other substances. Water molecules can be pulled through other substances. Water molecules being attracted to side of a small glass tube. A meniscus is the dip in the water surface due to this attraction. Water molecules attracted to paper towel

Low density of ice Less dense than water Floats on water Ice = 0.9164 g/ml Water = 0.9999 g/ml Floats on water Lakes and ponds freeze from top to bottom Insulates ponds from freezing solid Protects organisms in ponds and lakes Arrangement of ice provides s pace between molecules so it is lighter than water.

High Heat of Vaporization It takes a lot of energy for water to evaporate. This prevents excessive loss of water from lakes and ponds in summer. High heat causing water to evaporate.

High Specific Heat It takes a lot of energy to change the temperature of water. Water has the highest specific heat of all liquids except ammonia. Heat energy used to break molecules is not available for increased kinetic energy for evaporation. It would take more energy for evaporation. Larger numbers of water molecules per gram allows it to absorb more heat energy thus buffering against heat loss This helps to maintain constant temperature of oceans and body temperature. Substance   Specific Heat (cal/g-C)  Water        1.00  Aluminum        0.215  Iron        0.108 Gold        0.031  Specific Heat for water: It takes 1 calorie of energy to raise 1 gram of water I degree Celsius

Universal Solvent Ionic and polar substances dissolve best in water. Ionic and polar molecules have charges Water is attracted to parts of other molecules causing them to separate. (see below) Minerals and nutrients can be dissolved and transported more quickly and better throughout organisms. Main solvent in organisms.

Acids and Bases Acids have excess H+ ions. Bases have excess OH- ions. Neutral water has equal amounts of H+ and OH- ions. pH measures the concentration of H+ ions. pH scale ACIDS NEUTRAL BASES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 (Strongest) (Weakest) (Weakest) (Strongest)