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The Chemistry of Life: Chapter 2 Honors Biology  Why are we studying chemistry? Chemistry is the foundation of Biology Honors Biology ▪ Everything is made of matter ▪ Matter is made of atoms Hydrogen...

The Chemistry of Life: Chapter 2 Honors Biology  Why are we studying chemistry? Chemistry is the foundation of Biology Honors Biology ▪ Everything is made of matter ▪ Matter is made of atoms Hydrogen 1 proton 1 electron Oxygen 8 protons 8 neutrons 8 electrons Honors Biology Proton + Neutron 0 Electro – n  The World of Elements H C N O N M P S a C g K a Different kinds of atoms = elements Honors Biology  Honors Biology: Chapter 2 7 N 14 Honors Biology  Honors Biology: Chapter 2 1 H 1 Honors Biology  Honors Biology: Chapter 2 17 35 Cl Chlorine Honors Biology  Honors Biology: Chapter 2 26 56 Fe Iron Honors Biology  Life requires ~25 chemical elements ▪ About 25 elements are essential for life ◆ Four elements make up 96% of living matter: carbon (C) hydrogen (H) oxygen (O) nitrogen (N) ◆ Four elements make up most of remaining 4%: phosphorus (P) calcium (Ca) sulfur (S) potassium (K) Honors Biology  Bonding properties ▪ Effect of electrons ◆ electrons determine chemical behavior of atom ◆ depends on number of electrons in atom’s outermost shell ▪ valence shell How does this atom behave? Honors Biology  Bonding properties ▪ Effect of electrons ◆ chemical behavior of an atom depends on number of electrons in its valence shell How Honors does Biology this atom behave? How does this atom behave?  Elements & their valence shells Elements in the same row have the same number of shells Moving from left to right, each element has a sequential addition of electrons (& protons) Honors Biology  Elements & their valence shells Elements in the same column have the same valence & similar chemical properties Honors Biology  Chemical reactivity ▪ Atoms tend to ◆ complete a partially filled valence shell or ◆ empty a partially filled valence shell This tendency drives chemical reactions… and creates bonds – – – Honors Biology  Hydrogen bond Bonds in Biology H 2O ▪ Weak bonds ◆ hydrogen bonds ▪ attraction between + and – H 2O ◆ hydrophobic & hydrophilic interactions ◆ van derWaals forces Covalent bond ◆ (ionic) – ▪ Strong bonds ◆ covalent bonds – Honors Biology H2 (hydrogen gas)  Covalent bonds ▪ Why is this a strong bond? ◆ two atoms share a pair of electrons ◆ both atoms holding onto the electrons ◆ very stable ▪ Forms molecules H – H H—H O Oxyge – H n H HBiology Honors 2 (hydrogen gas) H2O (water)  Multiple covalent bonds ▪ 2 atoms can share >1 pair of electrons ◆ double bonds ▪ 2 pairs of electrons ◆ triple bonds ▪ 3 pairs of electrons ▪ Very strong bonds H – H–C– – Honors Biology H H  Polar covalent bonds ▪ Pair of electrons shared unequally by 2 atoms ▪ Water = O + H ◆ oxygen has stronger “attraction” for the + – electrons than hydrogen H – ◆ oxygen has higher electronegativity Oxyge ◆ water is a polar molecule n ▪ + vs – poles ▪ leads to many interesting H – properties of water… + – Honors Biology  Hydrogen bonding ▪ Polar water creates molecular attractions ◆ positive H atom in one H2O molecule attracted to negative O in another H2O ◆ also can occur wherever an -OH exists in a larger molecule ▪ Weak bond Honors Biology  Properties of Water Honors Biology  More about Water Why are we studying water? All life occurs in water ◆ inside & outside the cell Honors Biology  Chemistry of water ▪ H2O molecules form H-bonds with each other ◆ + attracted to – ◆ creates a sticky molecule The Power of Water Honors Biology  Elixir of Life ▪ Special properties of water ◆ cohesion & adhesion ▪ surface tension, capillary action ◆ good solvent ▪ many molecules dissolve in H2O ▪ hydrophilic vs. hydrophobic ◆ lower density as a solid ▪ ice floats! ◆ high specific heat ▪ water stores heat ◆ high heat of vaporization ▪ helps keep the body cool (sweat!) Honors Biology  Cohesion & Adhesion ▪ H bonding between H2O molecules is cohesion ◆ water is “sticky” ▪ surface tension ▪ drinking straw ▪ H bonding between H2O & other substances is adhesion ◆ capillary action ◆ meniscus ◆ water climbs up paper towel or cloth Honors Biology  How does H2O get to top of trees? Transpiration built on cohesion & adhesion Honors Biology  Water is the solvent of life ▪ Polarity makes H2O a good solvent ◆ polar H2O molecules surround + & – ions ◆ solvents dissolve solutes creating solutions Honors Biology  Do you dissolve in water? ▪ Hydrophilic ◆ substances have attraction to H2O ◆ polar or non-polar? Honors Biology  Or don’t you? ▪ Hydrophobic ◆ substances that don’t have an attraction to H2O ◆ polar or non-polar? Honors Biology fat (triglycerol)  The special case of ice ▪ Most (all?) substances are more dense when they are solid, but Not water… ▪ Ice floats! ◆ H bonds form a crystal Honors Biology  Ice floats Honors Biology  Why is “ice floats” important? ▪ Oceans & lakes don’t freeze solid ◆ surface ice insulates water below ▪ allowing life to survive the winter ◆ if ice sank… ▪ ponds, lakes & even oceans would freeze solid ▪ in summer, only upper few inches would thaw ◆ seasonal turnover of lakes ▪ cycling nutrients in autumn Honors Biology  Specific heat ▪ H2O resists changes in temperature ◆ high specific heat ◆ takes a lot to heat it up ◆ takes a lot to cool it down ▪ H2O moderates temperatures on Earth Honors Biology  Evaporative cooling Heat of vaporization Organisms rely on heat of Honors Biology vaporization to remove body heat  Ionization of water & pH ▪ Water ionizes ◆ H+ splits off from H2O, leaving OH– ▪ if [H+] = [-OH], water is neutral + ▪ if [H ] > [-OH], water is acidic ▪ if [H+] < [-OH], water is basic ▪ pH scale ◆ how acidic or basic solution is ◆ 0 → 7 → 14 H O → H+ + OH– Honors Biology 2  H+ Ion Examples of Solutions Concentratio p pH Scale n 100 H 0 Hydrochloric acid 10–1 1 10–2 2 Stomach acid, Lemon juice 10–3 3 Vinegar, cola, beer 10–4 4 Tomatoe s Black coffee, Rainwater 10–5 5 10–6 6 Urine, Saliva 10–7 7 Pure water, Blood 10–8 8 Seawate rBaking 10–9 9 soda 10–10 1 Great Salt Lake 10–11 01 Household 10–12 11 ammonia Household 10–13 2 1 bleach Oven cleaner 10–14 3 1 Sodium Honors Biology 4 hydroxide  Buffers & cellular regulation ▪ pH of cells must be kept ~7 ◆ pH affects shape of molecules ◆ shape of molecules affect function ◆ pH affects cellular function ▪ Control pH by buffers 9 8 ◆ reservoir of H+ 7 ▪ donate H+ when 6 Buffering 5 pH range [H+] falls 4 ▪ absorb H+ when 3 2 [H+] rises 1 0 Honors Biology 0 1 2 3 4 5 Amount of base added  What type of bear does not dissolve in water? ▪ A Non-Polar Bear! Honors Biology  Any Questions?!?!?! Honors Biology