Covalent Bonds Covalent bond A bond formed when two atoms share one, two, or three pairs of valence electrons Nonpolar covalent bond Valence electrons are shared equally Polar covalent bond Valence electrons shared unequally

Figure 2.5a-c Covalent bond formation Note the equal sharing of electrons. These are all nonpolar covalent bonds.

Figure 2.5e Covalent bond formation Note the unequal sharing of electrons. This is a polar covalent bond. The nucleus of the oxygen atom attracts the hydrogen atoms more strongly. The nucleus that attracts will have a slightly negative charge compared to the nucleus being attracted – that atom has a greater electronegativity.

Ionic and Covalent Bond Summary Ionic bond Nonpolar covalent bond Polar covalent bond What happens to the electron? Electron is donated by one atom and accepted by another Electron is shared equally between atoms Electron is shared unequally between atoms – it spends more time with the larger atom What is the charge distribution? + Charged cation - Charged anion No difference in charge distribution across the molecule Partial negative charge near the larger atom; partial positive charge near the smaller atom Example Na+Cl- CH4 H2O

Hydrogen Bonds Chemical Bonds

Hydrogen Bonds A special type of polar covalent bond that forms between hydrogen atoms and other atoms Different from other chemical bonds in that it produces intramolecular (not intraatomic) attractions between molecules

Figure 2.6 Hydrogen bonding among water molecules

Chemical Reactions

Chemical reactions Occur when new bonds form or old bonds break between atoms Metabolism – all chemical reactions occurring in the body.

Figure 2.7 The chemical reaction between two hydrogen molecules and one oxygen molecule to form two water molecules 02_01

Forms of Energy and Chemical Reactions

Energy Energy is the capacity to do work Potential energy is waiting to be used - stored Kinetic energy is being used - motion

Forms of Energy Chemical Electrical Mechanical Radiant

Law of Conservation of Energy Energy cannot be created nor destroyed. It can only be transferred from one form to another.

Energy Transfer in Chemical Reactions

Energy Flow in Chemical Reactions Release energy Exergonic reactions Require energy Endergonic reactions

Activation Energy and Catalysts the energy needed to break chemical bonds in the reactant molecule so a reaction can start Activation energy chemical compounds that speed up chemical reactions by lowering the activation energy needed for a reaction to occur (enzymes) Catalysts

Figure 2.8 Activation energy More energy released than absorbed = exergonic

Figure 2.9 Comparison of energy needed for a chemical reaction to proceed with a catalyst (blue curve) and without a catalyst (red curve)

Types of Chemical Reactions

Synthesis Reactions Small molecules combine to form large molecules Anabolic – bonds formed

Decomposition Reaction Large molecules break down into small molecules Catabolic – breaking bonds

Exchange Reactions Consist of both synthesis and decomposition reactions What we called replacement reactions

Oxidation-Reduction Reactions End products can revert to original combining molecules Almost all reactions in the body are reversible. Reversible Reactions Redox reactions  metabolism Transfer of electrons Oxidation = loss e- Reduction = gain e- OIL RIG Oxidation-Reduction Reactions

Inorganic Compounds and Solutions

Inorganic compounds Small molecules that do not contain carbon Water Acids and Bases Many salts Minerals

Water Inorganic Polarity Most abundant inorganic compound in the body (55-60% of body mass) Polarity Uneven sharing of valence electrons Partial negative charge near O Two partial positive charges near H Bent shape

Water Properties Is a solvent In a solution  Solvent dissolves solute Hydrophilic solutes easily dissolve in water Hydrophobic solutes do not easily dissolve in water Is an ideal medium for chemical reactions Hydrolysis reactions Dehydration synthesis reactions Has a high heat capacity It absorbs and releases heat without large changes in its own temperature Has a high heat of vaporization It requires a large amount of heat to change from a liquid to a gas Is a lubricant

Figure 2.10 How polar molecules dissolve salts and polar substances

Inorganic Compounds and Solutions Solutions, Colloids, and Suspensions Inorganic Compounds and Solutions

Mixtures Solution Colloid Suspension a mixture of mostly solvent with some solute Solution a mixture with large solutes that scatter light Colloid a mixture with large solutes that tend to settle out Suspension

Acids Dissociate in water to produce hydrogen ions (H+) and anions Are also called proton donors Have a pH < 7.0 Acid - dissociates in water to produce hydrogen ions (H+) and anions (-). Dissociation = ionization Also called a proton donor because H+ is a single proton with 1 positive charge. Example: HCl  H+ + Cl-

Bases Dissociate in water to produce hydroxide ions (OH-) and cations Are also called proton acceptors Have a pH > 7.0 Base - dissociates in water to produce hydroxide ions (OH-) and cations (+). Also called a proton acceptor because hydroxide ions attract protons. Removes H+ from a solution. Example: NaOH  Na+ + OH- And then….OH- + H+  H2O

Salts Dissociate in water to produce anions and cations other than H+ and OH- Are the products of acid-base chemical reactions Salt - dissociates in water to produce anions and cations other than H+ and OH- Often the product of an acid-base chemical reaction. Acids and bases react with one another to form salts. Example: HCl + KOH  H+ + Cl- + K+ OH-….And then H+ + Cl- + K+ OH-  KCl + H2O acid base dissociated ions salt water Essential source of electrolytes; make bones and teeth hard; essential for nerve and muscle function

Figure 2.11 Dissociation of inorganic acids, bases, and salts 02_01

Inorganic Compounds and Solutions Acid-Base Balance Inorganic Compounds and Solutions

Figure 2.12 The pH scale

Table 2.4 pH Values of Selected Substances

Buffer Systems Maintain pH by removing or adding hydrogen ions from a solution Carbonic acid – bicarbonate buffer system During acidosis: H+ + HCO3-  H2CO3 During alkalosis: H2CO3  H+ + HCO3-

Organic Compounds

Organic Compounds Carbohydrates Lipids Proteins Nucleic Acids Adenosine Triphosphate Organic compounds are relatively large carbon-based compounds. Important types of organic compounds are carbohydrates, lipids, proteins, nucleic acids, and adenosine triphosphate (ATP).

Carbon Is capable of forming up to 4 covalent bonds with other atoms Can form bonds with other carbons

Some Definitions Carbon skeleton Functional groups Monomer Polymer the chain of carbon atoms in an organic molecule Carbon skeleton other atoms or molecules bound to the carbon skeleton Functional groups a small organic molecule used to build macromolecules Monomer a macromolecule built from monomers Polymer

Table 2.5 Major Functional Groups

Carbohydrates Organic Compounds

Carbohydrates Include sugars, glycogen, starches, and cellulose Represent 2-3% of your body mass Main source of chemical energy for generating ATP A few are used as structural material Contain C, H, and O

Carbohydrates Many polar covalent bonds Most hydrophilic – soluble Watered carbon Monosaccharides, disaccharides, polysaccharides

Carbohydrate monomers Monosaccharides Carbohydrate monomers Contain 3-7 carbon atoms Pentose sugars Deoxyribose Ribose Hexose sugars Glucose Fructose Galactose

Figure 2.13 Alternative ways to write the structural formula for glucose 02_01

Figure 2.14 Monosaccharides 02_01

Disaccharides Formed by dehydration synthesis Biologically important examples Sucrose Lactose Maltose Broken down by hydrolysis

Figure 2.15 Disaccharides 02_01

Polysaccharides Glycogen Starches Cellulose Formed by dehydration synthesis Usually insoluble in water Biologically important examples Glycogen Starches Cellulose Broken down by hydrolysis

Figure 2.16 Part of a glycogen molecule – the main polysaccharide in the human body 02_01

Table 2.6 Major Carbohydrate Groups