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Properties of Water. What molecule supports all of life ?. Water Cycle. What is a polar molecule?. Has polar bonds: Water has polar covalent bonds Oxygen is more electronegative than H Electrons of covalent bonds spend more time closer to Oxygen than to H Creates a polar molecule
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What is a polar molecule? • Has polar bonds: • Water has polar covalent bonds • Oxygen is more electronegative than H • Electrons of covalent bonds spend more time closer to Oxygen than to H • Creates a polar molecule • O region is partially negative • H regions are partially positive • Causes the properties of water
– O POLAR MOLECULE H H + + H2O
– + Water (H2O) + Hydrogen bond – HYDROGEN BONDS Ammonia (NH3) + + +
How does this change when water is in different states? • Slightly positive H of 1 molecule is attracted to slightly negative O of nearby molecule creating a H bond that holds those molecules together
Hydrogen bonds Water and Polarity
What are the Properties of Water? • Adhesion • Cohesion • Surface Tension • High specific heat • Expands when frozen • Universal solvent
1. Cohesion • Cohesion – water “sticking” to itself
1. Cohesion • Cohesion contributes to transport of water and dissolved nutrients against gravity in plants
2. Adhesion Adhesion is water “sticking” to something else
Cohesion is supported by Adhesion • What is Adhesion? • clinging of one substance to another • Adhesion of water to cell walls by those same hydrogen bonds
3. Surface Tension • How is this related to Surface Tension? • Surface tension= how difficult it is to stretch or break the surface of a liquid
Benefits of properties 1-3: • Bugs that walk on water • Bugs that use air bubble to breathe underwater • Leads to transport of water and its dissolved nutrients against gravity in plants • Water molecules leaving plants by evaporation cause H bonds to tug on water molecules, creating an upward force of water in the plant
Hydrogen bonds Water and Temperature
4. High Heat Capacity a.k.a. High Specific Heat • Water’s temperature does not change easily • Water can absorb or release a good deal of heat before its overall temperature changes.
What is specific heat? • the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1 °C
Benefits of having a high heat capacity: • Keeps temperatures more constant in bodies of water so animals can survive better • Keeps water warm on a cool day and cool on a hot day, and in turn, cools the air around it on a hot day and heats air around it on a cool day • Keeps temperature from fluctuating greatly due to the fact that oceans cover the earth • Helps moderate Earth’s climate • Contributes to stability of temperature in lakes and ponds • Prevents land organisms for overheating
5.Expansion Upon Freezing • Water is less dense as a solid than as a liquid • Ice Floats • Begins freezing when its molecules are no longer moving vigorously enough to break their hydrogen bonds • Becomes about 10% less dense
Benefits of water expanding upon freezing: • Fish get to survive in cold temperatures • We get cold drinks
A few terms regarding solutions… • Solution- • Liquid that is completely homogeneous mixture of two or more substances • Solvent- • Dissolving agent of a solution • Solute- • Substance that is dissolved • Aqueous solution- • Solution in which water is the solvent
Why is water a versatile solvent? • Due to polarity of the ions • Ions have mutual affinity through electrical attraction of the opposite charges • Compounds don’t have to be ionic to dissolve water • Dissolve when water molecules surround each of the solute molecules, forming hydrogen bonds with them
Hydrophilic – any substance that “loves” water and dissolves easily into it • Hydrophobic – any substance that “hates” or repels water and will not mix with it
Benefits of water’s solubility: • Allows the movement of solvents through cohesion • Makes the solvent hydrophilic, benefitting cellular processes
QUIZ TIME! • The model illustrates hydrogen bonding found in water. This attraction between water molecules is the result of water’s • A ionic bonding. • B polar covalent bonding. • C positively charged atoms. • D negatively charged atoms.
