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Water: a special molecule • Water is the most common molecule on Earth & in living organisms. • Chemistry of living organisms takes place in water. Structure of The Water Molecule • H20 is polar: it has a negative end and a positive end. – Oxygen is negative – Hydrogen is positive – Polarity makes water a good solvent. – Most things dissolve in water: sugars, salts, etc. – Water is called the universal solvent Hydrogen Bonds • Water molecules are attracted to each other. • (-) Oxygen is attracted to the (+) Hydrogen of another water molecule • The attraction is called a Hydrogen bond. Hydrogen bonds are very weak Cohesion • Cohesion: Molecules of the same type are attracted to each other. – Surface tension is a result of cohesion. Think: This water strider is more dense than the water. Why doesn't it sink? Adhesion Adhesion: Molecules of different types are attracted to each other. Plants move water up stems in part due to adhesion. Water adhering to the sides of a test tube causes the meniscus Capillary action Capillary action is the combination of cohesion and adhesion. This is the reason water can move up a paper towel against the force of gravity. High heat capacity of water • Heat capacity is the amount of energy it take to raise the temperature of a substance 1°C. • Water must gain or lose a lot of energy for temperature to change. • Result: a stable aquatic environment & the internal environment of cells. Review Give an example, not used in this PowerPoint, of each of the special properties of water.