Water Notes

Biology, 9th ed,Sylvia Mader Chapter 02 Water Molecule Water is a POLAR molecule The oxygen atom “pulls” on electrons more than the hydrogen atoms. Because of this, oxygen has a slight negative charge and the hydrogens have a slight positive charge. Basic Chemistry

Because it is polar, it forms HYDROGEN BONDS Oxygen attracts the shared electrons and is partially negative. Hydrogens are partially positive. Ball-and-stick Model Electron Model Space-filling Model hydrogen bond a. Water (H2O) b. Hydrogen bonding between water molecules O 104.5° Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. + – Separate water molecules form temporary and brief bonds with nearby water molecules. The H of one molecule is attracted to the O from another

Properties of Water 1 and 2: Cohesion & Adhesion Biology, 9th ed,Sylvia Mader Chapter 02 Properties of Water 1 and 2: Cohesion & Adhesion Cohesion: Hydrogen bonds hold water molecules tightly together i.e. allows water to flow freely without molecules separating. Adhesion: Hydrogen bonds for between water and other polar materials Allow water be drawn many meters up a tree in a tubular vessel Basic Chemistry

Property 3: High Surface Tension Water molecules at surface hold more tightly than below surface Amounts to an invisible “skin” on water surface Allows small nonpolar objects (like water strider) to sit on top of water

Property 4: Capillary Action Biology, 9th ed,Sylvia Mader Chapter 02 Property 4: Capillary Action Water evaporates, pulling the water column from the roots to the leaves. Water molecules cling together and adhere to sides of vessels in stems. Water enters a plant at root cells. H2O Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Because of cohesion and adhesion, water has the ability to move through narrow spaces. This is why water seeps through a paper towel, and how it moves against gravity to the tops of trees Basic Chemistry

Property 5: Ice is less dense than water Biology, 9th ed,Sylvia Mader Chapter 02 4 100 1.0 0.9 Density (g/cm3) Temperature (ºC) liquid water ice lattice Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Property 5: Ice is less dense than water Frozen water less dense than liquid water Otherwise, oceans and deep lakes would fill with ice from the bottom up Ice acts as an insulator on top of a frozen body of water Melting ice draws heat from the environment Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ice layer Protists provide food for fish. River otters visit ice-covered ponds. Aquatic insects survive in air pockets. Freshwater fish take oxygen from water. Common frogs and pond turtles hibernate. Basic Chemistry

Biology, 9th ed,Sylvia Mader Chapter 02 Water: pH Scale pH value 10–1 10–2 10–3 10–4 10–5 10–6 10–7 10–8 10–9 10–10 10–11 10–12 10–13 10–14 10 0 Examples hydrochloric acid acidic basic stomach acid, lemon juice vinegar, cola, beer tomatoes black coffee urine pure water seawater baking soda Great Salt Lake household ammonia household bleach sodium hydroxide 1 2 3 4 5 6 7 8 9 10 11 12 13 14 H+ Ion Concentration Used to indicate acidic or basic a solution is Values range from 0-14 0 to <7 = Acidic 7 = Neutral >7 to 14 = Basic (or alkaline) Acids are usually sour to taste, bases are bitter. Basic Chemistry