• Why Is Water So Important to Life? Water makes up 60-90% body weight of most organisms. Special Properties of Water:Water molecules attract one another• __Cohesion__ -the molecules of a substance tend to stick together• _Hydrogen Bonding__ between water molecules produces high cohesion• Water cohesion explains how water molecules can form a chain in delivering moisture to the top of a tree (R- below- Fig. 2.8)• Cohesion of water molecules along a surface produces _surface tension__• Spiders and water striders rely on surface tension to move across the surface of ponds (L- Below)Water molecules _stick to polar or changed surfaces_ according to the property called _adhesion__• Adhesion helps water climb up the thin tubes of plants to the leaves_Water interacts___ with many other molecules• Water is an excellent _solvent___• A wide range of substances _dissolve___ (are completely surrounded and dispersed) in water to form __solutions____• Author Animation: Water as a solvent –Fig. 2-9• Water as a Solvent• Water interacts with many other molecules (continued)_Water soluble__ molecules are __hudrophilic__• Ex.- sugars and amino acidsWater-insoluble molecules are __hydrophobic________________________• Ex. – __fats and oil____• Water-based solutions can be __acidic, basic, or neutral_____A small fraction of water molecules break apart into ions (Fig. 2.11):H2O OH– + H+Solutions where H+ > OH– are acidic• For example, hydrochloric acid ionizes in water: HCl H+ + Cl–• Lemon juice and vinegar are naturally occurring acidsSolutions where OH– > H+ are __basic__• For example, sodium hydroxide ionizes in water: NaOH Na+ + OH–A base is a substance that combines with hydrogen ions (reducing their numbers.)• Baking soda, chlorine bleach, and ammonia are basic• The degree of acidity of a solution is measured using the _pH scale____• pH 0–6 is acidic (H+ > OH–)• pH 7 is neutral (H+ = OH–)• pH 8–14 is basic (OH– > H+)• The pH Scale – Fig 2.12Each unit on the pH scale represents a tenfold change in the concentration of H + ions .A __buffer__ helps maintain a relatively constant pH in a solution• A buffer is a compound that accepts or releases H+ in response to a pH change• The bicarbonate buffer found in our bloodstream prevents pH changes• If the blood becomes too acidic, bicarbonate accepts H+ to make carbonic acid HCO3– + H+ H2CO3 bicarbonate hydrogen ion carbonic acidBUT, if the blood becomes too basic, carbonic acid liberates hydrogen ions to combine with OH– to formwaterH2CO3 + OH– HCO3– + H2Ocarbonic acid hydroxide ion bicarbonate water• Water moderates the effects of temperature changeVery _low or high temperatures may damage enzymes__ or slow down important chemical reactionsThe energy required to heat 1 gram of a substance by 1°C is called its _specific heat__It takes a lot of energy to heat water. Heat speeds up the movement of molecules. To move, the hydrogen bonds must be broken first, leaving less energy to heat the water.• Why organisms can inhabit hot environments without overheating• Water moderates the effects of temperature change (continued)The ___heat of vaporization___ is the amount of heat needed to cause a substance such as water to evaporate (to change from a liquid to a vapor)Evaporating water uses up heat from its surroundings, cooling the nearby environment (as occurs duringsweating)It takes a lot of energy to cause water to evaporate• So very few molecules actually evaporate, the remaining water is cooled by losing those molecules.• Sunbathers don’t overheat. • Author Animation: Hydrogen Bonds and Specific Heat• Water’s High Specific Heat and High Heat of VaporizationWater forms an unusual solid: ice• __Most substances become denser___ when they solidify from a liquid• Ice is unusual because it is less dense than liquid water• Water molecules spread apart during freezingEffects:• Ice floats in liquid water• Ponds and lakes freeze from the top down and never freeze completely to the bottom• Many plants and fish are therefore saved from freezing• Water and Ice• Questions for Chapter 21. What is the stable part of an atom? The stable part of an atom is the nuclei which includes neutrons and protons. What does ‘atomic number’ mean? The atomic number just references to the number of protons in the atom.2. Explain inert and reactive elements. An inert element means that the particular element has the perfect amount of electrons in the outermost shell and can’t be altered in anyway. And a reactive element is just the exact opposite, these elements don’t have a full outermost shell and can share, gain, or lose electrons.3. What particles interact to form bonds? Electrons. What are ionic, covalent, and hydrogen bonds? Ionic bonds are bonds between two or more ions. Covalent bonds form between uncharged atoms that share electrons. Hydrogen bonds is the attractive forces between polar molecules.4. What are isotopes, free radicals, and antioxidants? Isotopes are elements with the same chemical properties but have different number of neutrons. Free radicals form when molecules have unpaired electrons in the outmost shell, free radicals also damage other cells. Antioxidants intercept the harmful effects of free radicals.5. How do we distinguish a molecule from a compound? Molecules can be between either the same or different elements through interactions on the outmost shell. While compounds can only be different elements that interact with each other.6. Explain the difference between a non-polar covalent bond and a polar covalent bond. Also, name some polar molecules. The difference between non-polar and polar covalent bonds is that a non- polar covalent bond equally shares the electrons and polar covalent means that they do not all share equally. Some examples are sugars, DNA, proteins7. Name the many special properties of water. Water makes up about 60- 90% of all organisms. Water molecules attract one another, resulting in cohesion (water molecules tend to stick together) and hydrogen bonding (high cohesion). Water molecules stick to polar or changed surfaces (adhesion.) Water interacts with many other molecules and is an excellent solvent.8. Name something that is neutral, acidic and basic. How does the pH scale work? Acidic: lemon juice and
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