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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
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Figure 2.5a-c Covalent bond formation
Note the equal sharing of electrons. These are all nonpolar covalent bonds.
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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.
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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
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Hydrogen Bonds Chemical Bonds
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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
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Figure 2.6 Hydrogen bonding among water molecules
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Chemical Reactions
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Chemical reactions Occur when new bonds form or old bonds break between atoms Metabolism – all chemical reactions occurring in the body.
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Figure 2.7 The chemical reaction between two hydrogen molecules and one oxygen molecule to form two water molecules 02_01
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Forms of Energy and Chemical Reactions
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Energy Energy is the capacity to do work
Potential energy is waiting to be used - stored Kinetic energy is being used - motion
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Forms of Energy Chemical Electrical Mechanical Radiant
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Law of Conservation of Energy
Energy cannot be created nor destroyed. It can only be transferred from one form to another.
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Energy Transfer in Chemical Reactions
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Energy Flow in Chemical Reactions
Release energy Exergonic reactions Require energy Endergonic reactions
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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
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Figure 2.8 Activation energy
More energy released than absorbed = exergonic
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Figure 2.9 Comparison of energy needed for a chemical reaction to proceed with a catalyst (blue curve) and without a catalyst (red curve)
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Types of Chemical Reactions
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Synthesis Reactions Small molecules combine to form large molecules
Anabolic – bonds formed
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Decomposition Reaction
Large molecules break down into small molecules Catabolic – breaking bonds
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Exchange Reactions Consist of both synthesis and decomposition reactions What we called replacement reactions
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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
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Inorganic Compounds and Solutions
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Inorganic compounds Small molecules that do not contain carbon Water
Acids and Bases Many salts Minerals
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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
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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
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Figure 2.10 How polar molecules dissolve salts and polar substances
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Inorganic Compounds and Solutions
Solutions, Colloids, and Suspensions Inorganic Compounds and Solutions
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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
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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-
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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
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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
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Figure 2.11 Dissociation of inorganic acids, bases, and salts
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Inorganic Compounds and Solutions
Acid-Base Balance Inorganic Compounds and Solutions
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Figure The pH scale
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Table 2.4 pH Values of Selected Substances
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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-
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Organic Compounds
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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).
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Carbon Is capable of forming up to 4 covalent bonds with other atoms
Can form bonds with other carbons
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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
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Table 2.5 Major Functional Groups
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Carbohydrates Organic Compounds
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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
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Carbohydrates Many polar covalent bonds Most hydrophilic – soluble
Watered carbon Monosaccharides, disaccharides, polysaccharides
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Carbohydrate monomers
Monosaccharides Carbohydrate monomers Contain 3-7 carbon atoms Pentose sugars Deoxyribose Ribose Hexose sugars Glucose Fructose Galactose
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Figure 2.13 Alternative ways to write the structural formula for glucose
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Figure 2.14 Monosaccharides
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Disaccharides Formed by dehydration synthesis
Biologically important examples Sucrose Lactose Maltose Broken down by hydrolysis
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Figure Disaccharides 02_01
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Polysaccharides Glycogen Starches Cellulose
Formed by dehydration synthesis Usually insoluble in water Biologically important examples Glycogen Starches Cellulose Broken down by hydrolysis
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Figure 2.16 Part of a glycogen molecule – the main polysaccharide in the human body
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Table 2.6 Major Carbohydrate Groups
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