Water’s Life support Properties Text pg. 25 - 26

Polar Covalent Bonds Water has atoms with different electronegativities Oxygen attracts the shared electrons more strongly than hydrogen So, the shared electrons spend more time near oxygen The result is a polar covalent bond In H2O the oxygen atom has a slight negative charge and the hydrogens have a slight positive charge Molecules with this unequal distribution of charges are called polar molecules

Hydrogen Bonds Hydrogen, within a polar covalent bond, is attracted to electronegative atoms in other molecules. called a hydrogen bond

Cohesion Hydrogen bonding causes molecules to stick together, a property called cohesion Cohesion is related to surface tension - a measure of how difficult it is to break the surface of a liquid Hydrogen bonds are responsible for surface tension

Adhesion Adhesion is the clinging of one substance to another unlike itself. Caused by adhesion the water runs along the glass and does not fall straight.

Adhesion & Cohesion results in Capillary Action! Capillary Action is how plants obtain water through their root systems, despite gravity! Cohesion Direction of water movement Water-conducting cells

Water’s hydrogen bonds moderate temperature Has a greater ability to resist temperature change because of hydrogen bonds. Heat is the energy associated with movement of atoms and molecules in matter Temperature measures the intensity of heat

Difference between heat and temperature. To raise the temperature, heat must break hydrogen bonds. With so many hydrogen bonds between water molecules, it can absorb a great deal of heat, with only a slight temperature change. Compare the water in a pool on a hot day, and a metal chair next to the pool!

Water’s heat capacity in nature Large bodies of water can store huge amounts of heat from the sun, which can be later given off as it cools – heating the air. Water resists temperature changes also stabilizes ocean temperatures (good for marine life). 70% of our bodies are made of water, which helps moderate our internal temperature

Ice When water freezes, each molecule forms a stable hydrogen bond with four neighbors A three-dimensional crystal results There is space between the water molecules Ice is less dense than water, so it floats

Ice Water molecules Are spaced out Liquid water Water molecules are closer together

Ice in nature Prevents ponds & lakes from freezing solid. Floating ice insulates the water below from the cold air above. This floating ice acts as a “blanket” allowing fish and other aquatic forms of life to survive.

Ice in the Artic Provides a hunting ground for polar bears Deflects heat from the Earth.