2 Water One side is more positive One side is more negative Water is composed of one atom of oxygen and two atoms of hydrogen held together by covalent bonds (H2O)Water is a Polar Molecule unequal distribution of chargesOne side is more positiveOne side is more negativeWhen water molecules are close, their opposite sides are attracted to each other because of polarityThis attraction between water molecules is responsible for most of the properties of water.
3 Polar and Nonpolar Molecules Polar Molecule – Unequal distribution of chargesOne side is more positiveOne side is more negativeDissolves in waterEx: WaterNonpolar Molecule – no separation of charge, so no positive or negative poles are formed.Do not dissolve in waterEx: CO2, O2, lipidsThink of the interaction of two magnets and how they either are attracted to each other or repel.
4 How do water molecules interact with each other? Polar water molecules can be attracted to each otherThe hydrogen atom with its’ partial positive charge (+) is attracted to the oxygen atom (partial negative charge) of a different water molecule!This is known as a hydrogen bond
5 Hydrogen Bonds Bonding between molecules Very weak, but very important for the variouscharacteristics of of water…
6 Covalent bonds internally hold a water molecules together Different water molecules are held together by hydrogen bonds – very weak bondsCovalentHydrogen
7 5 Characteristics of Water 1. Cohesion 2. Adhesion 3. High Specific Heat 4. Less Dense as a Solid 5. Water is a terrific solvent
8 Water Properties **H-bonding is responsible for these properties 1. Cohesion (“co-” means “together”)the attraction between molecules of the same substance (water)Tendency of molecules of the SAME “kind” to stick together2. Surface Tension:Measure of how difficult it is to stretch or break the surface of a liquid/ resist an external force.H2O has high surface tensionDue to H-bonds
10 Surface tension another type of cohesion a measure of how difficult it is to stretch or break the surface of a liquidWater molecules form a “barrier” by H-bonding togetherWater does NOT pull apart very easily acts like elastic
11 2. AdhesionAdhesion = The type of attraction that happens between two different moleculesGlass, soil, plant tissue, cotton, etc.Forms stronger bonds than cohesionExample:Meniscus forming on graduatedcylinder!Capillary action- seen in plants,trees and with straws too!
15 High Specific HeatThe temperature of water does not increase or decrease easilyWater has to absorb more heat energy to increase overall temperature compared to other compoundsEx: Lake Michigan is really cold until ~ August…it takes a long time to warm up!!Helps to regulate cell temperatures in organismsDue to the fact that the molecules hold each other together, the temperature of water does not rise or fall very easily
16 Water has a high specific heat so its temperature does NOT fluctuate very much allows life to live in watermoderate Earth's climate by buffering large fluctuations in temperature.
18 4. Low Density in Solid Form Allows for insulation of bodies of water by floating iceSolid water (i.e.-ice)Is less dense than liquid waterFloats in liquid waterSince ice floats in water Life can exist under frozen surfaces of lakes/polar seas
19 Ice floats because ice is less dense than liquid water! This is because the H bonds hold the water molecules farther apart than in liquid water
20 The hydrogen bonds in ice Are more “ordered” than in liquid water, making ice less denseLiquid waterHydrogen bonds constantly break and re-formIceHydrogen bonds are stable
21 5. Water as a Solvent What is a solution? A solution is a mixture of substances looks the same throughoutMade up of a solute and a solventWater is a GREAT solvent (Water is the universal solvent)Solute – gets dissolved (Hot Cocoa mix)Solvent – does the dissolving (Water)Solution – uniform mixture of two or more substances
22 Hydrophilic and Hydrophobic Substances A hydrophilic substanceHas an affinity for waterWater “loving”Dissolves in waterExample: salt and sugarA hydrophobic substanceDoes not have an affinity for waterWater “fearing”Does NOT dissolve in waterExample: Oil
23 REVIEW Where is the Polar Covalent Bond in water? What is the difference btw a “POLAR COVALENT BOND” and a “NONPOLAR COVALENT BOND?
24 Acids and BasesAn acidcompound that releases/donates a proton (H+) when dissolved in waterIncreases H+ concentration in solutionEx: HClA basecompound that accepts H+ and removes them from a solutionIs any substance that reduces the hydrogen ion concentration of a solutionThe more basic the solution, the higher the OH- concentrationEx: NaOHpHMeasure of acidity or alkalinity of an aqueous solution
25 What is the pH scale? Identifies acids and bases Indicates concentration of H+ ions in a solutionpH 7 = Neutral = concentration of H+ and OH- are equal
26 How do you read the pH scale? pH of 7NeutralConcentration of OH- and H+ are equalEx – WaterpH 1 – 6.5AcidMore H+ than OH-Ex – Lemon juice / HClpH 7.5 – 14BaseMore OH- than H+Ex – Baking soda / ammonia
27 What is a buffer? Buffers prevent drastic changes in pH Buffers: weak acids or bases that can react with strong acids or bases to prevent sudden changes in pHWhy are buffers important?Key in regulating our urinary, circulatory, and blood pHNecessary in maintaining homeostasisBuffers prevent our blood from becoming too acidic, our lungs/muscles from becoming over saturated in CO2
28 the lower the pH the stronger the acid the higher the pH the stronger the basepH 7.0 is neutral