Unit 1: Biochemistry I. Chemical Bonding

 Compound—a substance consisting of two or more different elements combined in a fixed ratio Sodium ChlorideChlorineSodium +

 Many of the compounds in living organisms contain carbon, hydrogen, oxygen, and nitrogen –DNA, for example, contains all four of these elements  Different arrangements of elements provide unique properties for each compound  Only valence electrons (in the outermost energy level) are involved in chemical bonding  Atoms want to fill their outer energy levels by forming compounds.

Magnesium Lithium Hydrogen Third shell First shell Second shell Sodium Beryllium Aluminum Boron Silicon Carbon Phosphorus Nitrogen Sulfur Oxygen Chlorine Fluorine Argon Neon Helium

A. Ionic Bond- formed when two ions with opposite charges attract each other Due to transfer of valence electrons cation (+) & anion (-) = ionic compound metal & non-metal stronger bonds, solids (at room temp), higher melting points

Na Sodium atom Transfer of Valence electron Cl Chlorine atom Na + Sodium ion Cl – Chloride ion Sodium chloride (NaCl) + –

Na + Cl –

B. Covalent bond- formed when atoms share valence electrons compound is called a molecule 2 or more non-metal elements weaker than ionic bond, can be solid liquid or gas, low melting points

1. nonpolar covalent bonds – equal sharing of valence electrons ex: H 2, O 2, CH 4 2. polar covalent bonds – unequal sharing of valence electrons one atom attracts electrons stronger than the other ex: H 2 O referred to as a polar molecule

(–) O HH (+)

II. Water’s Life Supporting Properties When hydrogen is part of a polar covalent bond it can form attractions with other atoms (ex: O, N, F) This attraction is called a hydrogen bond (weaker than covalent bond; not really a bond) The H of one water molecule is attracted to the O end of a nearby water molecule due to hydrogen bonding

Hydrogen bond

1. Cohesion - hydrogen bonding causes molecules of the same substance to stick together stronger for water than other liquids useful in plants that depend upon cohesion to help transport water and nutrients up the plant related to surface tension - a measure of how difficult it is to break the surface of a liquid

2. Adhesion – attraction between 2 different substances water forms hydrogen bonds with other substances like plant tissue and glass. causes meniscus in graduated cylinder capillary action- adhesion between water and glass causes water to rise in a narrow tube against the force of gravity.

Water-conducting cells Adhesion Cohesion 150 µm Direction of water movement

3. High Specific Heat- amount of energy required to raise 1 g of a substance 1°C. due to hydrogen bonding, water has a greater ability to resist temperature change than other liquids makes water a good insulator

4. Water’s Density When water freezes, each molecule forms a stable hydrogen bond with four neighbors A three-dimensional crystal results There is space between the water molecules Ice is less dense than water, so it floats

Liquid water Hydrogen bonds constantly break and re-form Ice Hydrogen bonds are stable Hydrogen bond

5. Universal Solvent Water is the greatest solvent on Earth. Water's polarity gives it the ability to dissolve both ionic compounds and other polar molecules, such as sugar. (like dissolves like) A solution is a uniform mixture of two or more substances dissolving agent =solvent substance dissolved= solute Copyright © 2009 Pearson Education, Inc.

Ion in solution Salt crystal

The ions gradually become dispersed in the water, forming a solution.

III. pH Scale some water molecules break apart into ions  hydrogen ions (H + )  hydroxide ions (OH – ) Both are extremely reactive A balance between the two is critical for chemical processes to occur in a living organism Buffers minimize pH changes in humans by absorbing H + or OH -

A. Acids - chemicals other than water that can contribute H + to a solution  Ex: HCl (gastric acid) in your stomach that aids in digestion  An acidic solution has a higher concentration of H + than OH –

B.Bases -chemicals that contribute OH - to a solution  Ex: sodium hydroxide (NaOH) provides OH –  Basic solutions have a higher concentration of OH – than H +

Acidic solution Neutral solution Basic solution

C.pH scale (pH = potential of H + ) describes whether a solution is acidic or basic  ranges from 0 (most acidic) to 14 (most basic)  neutral (pH = 7)  pH<7 = acid  pH>7 = base

Acidic solution pH scale Battery acid Lemon juice, gastric juice Grapefruit juice, soft drink, vinegar, beer Tomato juice Rain water Human urine Saliva Pure water 6 7 Human blood, tears Seawater Milk of magnesia Household ammonia Household bleach Oven cleaner Neutral solution Basic solution NEUTRAL [H + ]=OH – ] Increasingly ACIDIC (Higher concentration of H + ) 14 Increasingly BASIC (Lower concentration of H + )

IV. Chemical Reactions C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O reactants products

electron transfer between atoms creates electron sharing between atoms creates Chemical Bonds atomic number of each element water nonpolar covalent bonds (e) ions (f) (g) (h) attraction between ions creates unequal sharing creates can lead to example is equal sharing creates has important qualities due to polarity and have positively charged have neutral have negatively charged number in outer shell determines formation of number may differ in number present equals (a) Atoms (b) (c) (d)

atomic number of each element have positively charged have neutral have negatively charged number in outer shell determines formation of number may differ in number present equals (a) Atoms (b) (c) (d)

electron transfer between atoms creates electron sharing between atoms creates Chemical Bonds water nonpolar covalent bonds (e) ions (f) (g) (h) attraction between ions creates unequal sharing creates can lead to example is equal sharing creates has important qualities due to polarity and