WATER AND THE FITNESS OF THE ENVIRONMENT WATER

Chemistry of water Water is a POLAR molecule. This means it has covalent bonds that do not share electrons equally. The oxygen is slightly negative, the hydrogens are slightly positive.

Chemistry of Water Water molecules form HYDROGEN BONDS with other water molecules. The positive Hs are attracted to negative Os This creates a weak bond, and a ”sticky” molecule

Special Properties of Water Because of Hydrogen bonding Cohesion Adhesion Surface Tension Ice Floats High Specific Heat Evaporative Cooling Universal Solvent Forms ions in water

Cohesion Hydrogen bonds between water molecules creates cohesion, where water sticks to other water molecules  Drinking water through a straw  Water moving up a tree

Adhesion Water molecules can stick to other things because of hydrogen bonds, this is called adhesion  Water climbing up a paper towel  A meniscus in a graduated cylinder  Dew drops on plant leaves

Surface Tension On the tops of bodies of water, molecules on the surface stick to each other, causing surface tension.  Bugs and lizards can “walk” across the top of water

Ice floats Ice is less dense than liquid water, so ice floats Hydrogen bonds form a crystal with a loose structure and space between the molecules Molecules are further apart and less dense Ponds don’t freeze solid in winter

High specific heat Water has high specific heat, it takes a lot of energy to change the temperature of water because of the hydrogen bonds This helps moderate the temperatures on Earth

Evaporative cooling As we sweat, water turns from liquid to gas. As the water evaporates, the body’s temperature is lowered. Hydrogen bonds are broken, and heat is released.

Universal Solvent Water is a good solvent due to its polarity  Polar = Charged = Hydrophilic = dissolves in water  Non-polar = Not charged = Hydrophobic = won’t dissolve Polar molecules surround positive and negative ions Solvents dissolve solutes creating aqueous solutions

Forms ions A hydrogen ion (H + ) splits off from water to leave a hydroxide ion ( - OH) H > H OH If the concentration of the 2 ions is equal, water is neutral If there are more hydrogen ions (H+), water is acidic If there are more hydroxide ions (OH-), water is basic