Chemistry of Life

1. microcosm.web.cern.ch Chemistry of Life “Life is just a series of chemical reactions.” LECTURE #2

2. Composition Elements are substances that can’t be broken down to other particles by ordinary means. More than 100 elements known…

3. south.mpls.k12.mn.us Hydrogen, carbon, nitrogen and oxygenare the most common elements (99%)of living organisms. Atomic Number = number of protons

4. Composition Elements are substances that can’t be broken down to other particles by ordinary means. An atom is the smallest unit of an element that still retains the properties of that element. • Protons = positive charge • Neutrons = no charge • Electrons = negative charge

5. Unbalanced atoms… • Isotopes: Atoms of elements that have differing numbers of neutrons. • 99% of carbon on Earth is Carbon-12 (6 neutrons, 6 protons) • But there’s also Carbon-13 (7 neutrons) and Carbon-14 (8 neutrons) • Radioisotopes: atoms with a dissimilar number of protons and neutrons (e.g. Carbon-14). • Rare. Unstable. • Emit electrons. • Used for radioactive dating, tracking chemicals, etc.

6. Matter is transformed through chemical bonding • A few rules… • Energy seeks its lowest state (e.g. rock on a hill) • Atoms do this by completing their outer “electron shell” Shell #1 is full when it has 2 electrons (All other shells need 8 electrons) Result = Atoms with unfilled shells are more likely to bond with other atoms. Hydrogen Helium

7. Types of bonds • Covalent bonding • Atoms share electrons • Molecules are formed (e.g. molecular hydrogen, water) Nonpolar covalent bond = Equal “pull” from all atoms. Polar covalent bond = One atom exerts more force and has a partial negative charge.

8. Types of bonds • Ionic bonding • Association between a positive atom (has lost 1 or more electrons) and a negative atom (has gained 1 or more electrons). • Bonding is a result of mutual attraction.

9. Table salt is the result of an ionic bond planetgreen.discovery.com belmontfrontporch.wordpress.com

10. Types of bonds • Hydrogen bonding • A weak association between an electronegative atom and a hydrogen atom that’s already in a covalent bond. • These bonds are very common. • These bonds are easily broken. • Reason why water has such unique properties!

11. Properties of WaterThermal conductivity= Heat spreads rapidly through water.High specific heat = Water requires a lot of energy to raise its temperature by 1 degree Celsius. • High boiling point = Water requires a lot of energy to break its hydrogen bonds and become a gas. • Evaporative cooling = Animals sweat/pant to release heat generated by metabolism. horseguidelines.com

12. Cohesion = molecules hold togetherAdhesion = attachment of different substances to water • High freezing point = 32 F • Less dense as solid =ice floats

13. Recap… • Elements are substances that can’t be broken down by ordinary means. (EX: Carbon, gold, helium) • Atoms are the smallest units of elements. • Contain protons (+), electrons (-) and neutrons (no charge). • Electrons determine the chemical properties of elements. • To be stable, atoms want their outer electron shellto be FILLED = 8 electrons for most elements. • Chemical reactions involve sharing or exchanging electrons.

14. Recap… • A molecule is 2+ atoms joined by a chemical bond. Covalent bond = atoms share electrons (H2O) Ionic bond = one atom donates electron to the other (Na+Cl-) • Bonds contain energy and therefore take energy to break. • Oxygen is electronegative (“electron-loving”) and creates the partial negative pressure in water molecules that encourages hydrogen bonding… … and give water its unique properties.

15. Water and pH When a water molecule dissociates (comes apart) it forms a H+ ion and an OH- ion. pH is a measure of acidity (+) or alkalinity (-) • ACIDIC solutions have low pH, which means there is an abundance of H+ ions  acids donate H+ • BASIC or ALKALINE solutions have high pH, which means there is an abundance of OH- ions  bases accept H+ • NEUTRAL solutions (pH=7) have a balance of these ions.

16. pH is on a LOG SCALE. So something with a pH of 6 has 10 times the concentration of H+ as one with a pH of 7. Eggs Oranges Coffee Bananas

18. Acids & Bases • Acids and bases are very corrosive/caustic substances • Can damage proteins, cells and tissues • pH in the body is under homeostatic control • Blood pH = 7.4 • Human cell pH = 7 • Human urine – 4.4 to 8 (usually ~6) • Stomach pH = 1 • Buffer = a substance that helps stabilize pH • EX: Antacids that control the acidity of your stomach.

19. Acid Rain is pH < 5.6 COMBINING… • Sulfur dioxide (SO2) from oil-burning plants. • Nitric oxide (NO) from car emissions. • Hydroxyl radicals (OH) in the atmosphere. PRODUCES… • Sulfuric acid (H2SO4) • Nitric acid (HNO3) RESULTS… Soil and organism pH balances are disrupted EX: Leached metals (Al)destroy roots and fish gills. blog.lib.umn.edu/harse003/architecture whoooaaa.wikispaces.com http://www.youtube.com/watch?v=RP-sU8i2edo http://www.5min.com/Video/Coal-Combustion-and-Acid-Rain-1354362 dsc.discovery.com

20. Water’s polarity facilitates reactions • Solute = What is being dissolved • Solvent = Liquid that dissolves solute • Solution = A mixture of 2+ molecules, atoms or ions that is homogeneous throughout. The sodium (+) atoms in salt are attracted to the oxygen (-) and the and chlorine (-) atoms are attracted to the hydrogen (+) atoms. en.wikibooks.org

21. Na+Cl- crystal structure Na+Cl- dissociates in H2O

22. Hydrophobic vs. Hydrophilic • When talking about the way compounds interact in water, we can say that they are either… • Hydrophobic = “water fearing”  NONPOLAR  Repelled by water; don’t mix in solutions - Carbon- and hydrogen-based compounds (CH) • Hydrophilic = “water loving”  POLAR Has an affinity for water and can dissolve in water - Hydroxyl groups (OH) - Any molecules with a + or - charge