WATER AND SOLUTIONS PAGE BIOLOGY

LECTURE 1 OBJECTIVES BY THE END OF THIS LECTURE, YOU WILL BE ABLE TO:  1. Explain how water’s polar nature affects its ability to dissolve substances.  2. Outline the relationship between hydrogen bonding and the different properties of water.

CORNELL NOTES

WATER! Water is essential to life because of its structure The water molecule is one oxygen atom and two hydrogen atoms that are bonded COVALENTLY (they share electrons) See pics on page 39 of text

POLARITY The total charge on a water molecule is NEUTRAL (no charge) BUT the charge is not the same on both sides Water is called a POLAR molecule because the charge is different on 2 sides

SOLUBILITY OF WATER Because a water molecule is POLAR, other polar molecules will dissolve easily in water OPPOSITES ATTRACT!

HYDROGEN BONDING Because water is POLAR water molecules stick to themselves Water molecules are held to each other by HYDROGEN BONDS These bonds form, break, and reform A LOT

1 st PROPERTY OF WATER: Water molecules sticking to each other is called COHESION Water molecules sticking to something else (like glass) is called ADHESION

2 nd PROPERTY OF WATER: TEMPERATURE MODERATION  Water has a HIGH HEAT CAPACITY, which means it can absorb or release a lot of energy without a big change in temperature  The temperature of water goes up only after all the hydrogen bonds are broken

Examples:  Example: The oceans stabilize global temperatures  Example: Organisms can keep their cells (that are mostly water) the same temp. even though the outside temp. changes  Example: Sweating water which releases body heat

3 rd PROPERTY OF WATER: DENSITY OF ICE:  Because the hydrogen bonds form at a certain angle there is a lot of space between molecules when frozen  So, ice (which is a SOLID) is LESS dense than water (which is a LIQUID)  Bodies of water freeze from top down, allowing life to exist below icy surface

REVIEW: 1. Explain how water’s polar nature affects its ability to dissolve substances: 2. Outline the relationship between hydrogen bonding and the different properties of water: