The Chemical Basis of Life

1. The Chemical Basis of Life Energy levels of electrons *chemical behavior due to electrons Electron configuration and chemical properties:

2. Covalent Bonds • A covalent bond forms when two atoms share one or more pairs of outer-shell electrons. • Atoms held together by covalent bonds form a molecule. Name molecular formula Electron configuration Structural formula Space-filling model Ball-and-stick model Hydrogen gas H2 Single bond a pair of shared electrons Oxygen gas O2 Double bond two pairs of shared electrons Methane CH4

3. Ionic Bonds • When an atom loses or gains electrons, it becomes electrically charged. • Charged atoms are called ions. • Ionic bonds are formed between oppositely charged ions. The outer electron is stripped from sodium and completes the chlorine atom’s outer shell Outer shell has 1 electron Complete outer shells Outer shell has 7 electrons The attraction between the ions—an ionic bond—holds them together Na Sodium atom Cl Chlorine atom Na Sodium ion Cl Chlorine ion Sodium chloride (NaCl)

4. Hydrogen Bonds • Water is a compound in which the electrons in its covalent bonds are shared unequally. • This causes water to be a polar molecule, one with opposite charges on opposite ends. slightly  slightly  H H O slightly –

5. Hydrogen bonding • Weak bonds formed between hydrogen and another atom • Surface tension of water • Important as intramolecular bonds, giving shape to proteins and other biomolecules

6. WATER AND LIFE • Life on Earth began in water and evolved there for 3 billion years. • Modern life remains tied to water. • Your cells are composed of 70%–95% water.

7. Properties of Water • Numerous properties due to the hydrogen bonding

8. Properties of Water • Cohesion • Adhesion Evaporation from the leaves Microscopic tubes Cohesion due to hydrogen bonds between water molecules Flow of water SEM

9. Properties of Water • Heat and temperature • Water can absorb and store large amounts of heat while only changing a few degrees in temperature. • Water can moderate temperatures.

10. Properties of Water • Surface tension is the measure of how difficult it is to stretch or break the surface of a liquid.

11. Water is the solvent of life *solution *solvent *solute *aqueous solution

12. The Chemical Basis of Life H2O H+ + OH- *hydrophilic *hydrophobic Hydrophilic and hydrophobic substances The dissociation of water molecules *acid *base Acids and bases

13. 14 Acids, Bases and pH Oven cleaner 13 Household bleach 12 Household ammonia 11 Increasingly basic lower Hconcentration Basic solution Milk of magnesia 10 9 Seawater 8 Human blood Pure water 7 Neutral [H+]  [OH–] 6 Urine Neutral solution 5 Tomato juice 4 Increasingly acidic greater Hconcentration Grapefruit juice, soft drink 3 2 Lemon juice, gastric juice 1 Acidic solution 0 pH scale

14. Carbon and Organic Chemistry • Carbon is a versatile atom. • Carbon forms large, complex, and diverse molecules necessary for life’s functions. • Organic compounds are carbon-based molecules. Structural formula Ball-and-stick model Space-filling model

15. Carbon and Organic Chemistry Carbon skeletons vary in length • Variations in Carbon skeletons Carbon skeletons may be unbranched or branched Carbon skeletons may have double bonds, which can vary in location Carbon skeletons may be arranged in rings

16. Hydrocarbons • Larger hydrocarbons form fuels for engines. • Hydrocarbons of fat molecules fuel our bodies.

17. Chemical Components of Cells *structural isomers Example of enantiomers: *geometric isomers *enantiomers