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

a pair of shared electrons two pairs of shared electrons 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 Hydrogen gas H2 Oxygen gas O2 Methane CH4 Electron configuration Structural formula Space-filling model Ball-and-stick model Single bond a pair of shared electrons Double bond two pairs of shared electrons

Sodium chloride (NaCl) 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. Outer shell has 1 electron has 7 electrons The outer electron is stripped from sodium and completes the chlorine atom’s outer shell Na Sodium atom Cl Chlorine atom Complete outer shells The attraction between the ions—an ionic bond—holds them together Na Sodium ion Cl Chlorine ion Sodium chloride (NaCl)

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 –

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

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.

Properties of Water Numerous properties due to the hydrogen bonding

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

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.

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

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

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

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

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

Carbon and Organic Chemistry Variations in Carbon skeletons Carbon skeletons vary in length 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

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

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

Carbon and Organic Chemistry The unique properties of an organic compound depend not only on its carbon skeleton but also on the atoms attached to the skeleton These atoms are called functional groups Some common functional groups include: Hydroxyl group Carbonyl group Amino group Carboxyl group Found in alcohols and sugars Found in amino acids and urea in urine (from protein breakdown) Found in amino acids, fatty acids, and some vitamins Found in sugars