New streamlined coverage of elimination and substitution; synthesis skill-building applications; updated problem-solving strategies; and tutorials guide college students throughout fundamental and complex content in both the first and second semesters of the course. Note: You are purchasing a standalone product; MasteringChemistry does not come packaged with this content.
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Preparing Students for Future Study in a Variety of Scientific Disciplines This book organizes the functional groups around mechanistic similarities. When students see their first reaction other than an acid—base reaction , they are told that all organic compounds can be divided into families and that all members of a family react in the same way.
And to make things even easier, each family can be put into one of four groups, and all the families in a group react in similar ways. It lets students see where they have been and where they are going as they proceed through each of the four groups.
It also encourages them to remember the fundamental reason behind the reactions of all organic compounds: electrophiles react with nucleophiles. When students finish studying a particular group, they are given the opportunity to review the group and understand why the families came to be members of that particular group. The four groups are covered in the following order. However, the book is written to be modular, so they could be covered in any order. These compounds are nucleophiles and, therefore, react with electrophiles—undergoing electrophilic addition reactions.
These compounds are electrophiles and, therefore, react with nucleophiles—undergoing nucleophilic acyl substitution, nucleophilic addition, and nucleophilic addition-elimination reactions. Some aromatic compounds are nucleophiles and, there- fore, react with electrophiles—undergoing electrophilic aromatic substitution reactions.
Other aromatic compounds are electrophiles and, therefore, react with nucleophiles—undergoing nucleophilic aromatic substitution reactions. The organization discourages rote memorization and allows students to learn reactions based www. It is only after these patterns of reactivity are understood that a deep understanding of organic chemistry can begin. As a result, students achieve the predictive capacity that is the beauty of studying science.
A course that teaches students to analyze, classify, explain, and predict gives them a strong foundation to bring to their subsequent study of science, regardless of the discipline. Instead, they learn about the synthesis of alkyl halides, alcohols, ethers, epoxides, alkanes, etc. The synthesis of alkenes is not covered until the reactions of alkyl halides and alcohols are discussed—compounds whose reactions lead to the synthesis of alkenes.
It also results in a certain economy of presentation, allowing more material to be covered in less time. For this reason, lists of reactions that yield a particular func- tional group are compiled in Appendix III. Helping Students Learn and Study Organic Chemistry As each student generation evolves and becomes increasingly diverse, we are challenged as teachers to support the unique ways students acquire knowledge, study, practice, and master a subject. This will allow them to study more efficiently with the text.
The book is written much like a tutorial. Each section ends with a set of problems that students need to work through to find out if they are ready to go on to the next section, or if they need to review the section they thought they had just mastered.
Margin notes throughout the book succinctly repeat key points and help students review important material at a glance. Organizational Changes Using the E,Z system to distinguish alkene stereoisomers was moved to Chapter 4, so now it appears immediately after using cis and trans to distinguish alkene stereoisomers. Moving this has another advantage—because catalytic hydrogenation is the only reaction of alkenes that does not have a well-defined mechanism, all the remaining reactions.
Chapter 8 starts by discussingwill Problems of this kind theappear structurerepeatedly of benzenethroughout becausetheit isbook, because the ideal solvingto compound them use is fun and is a good way to learn organic chemistry. This chapter also includes a discussion on aromaticity, so a short introduction to electrophilic aromatic substitution reactions is now included.
This allows students Example 1 to see how aromaticity causes benzene to undergo electrophilic substitution rather than electrophilic addition—the Starting reactions with 1-butyne, howthey justyou could finished makestudying.
You can use any reagents you need. Traditionally, electronic effects are taught so students can O understand the activating and directing effects of substituents on benzene rings. Therefore, in this edition electronic Many effects chemists arethat find discussed the easiestin Chapter 8 and used way to design to teachis students a synthesis how substituents to work backward.
Insteadaffect the of look- pKaat ing values of phenols, the reactant and benzoic decidingacids, how andto doanilinium the firstions.
The product The two chapters of theinsynthesis the previous is a edition ketone. We will into useone thechapter Chapter addition acid-catalyzed 9. The recent compelling of water evidence to an alkyne. Youshow- also ing that could usealkyl halides do not undergo S hydroboration—oxidation. Thus, 3-hexyne is the alkyne that should be used for Ithe have found that synthesis of theteaching desiredcarbonyl ketone.
If students understand this, then carbonyl chemistry becomes relatively easy. I synthesize each functional group. To produce the desired six-carbon product, a two-carbon alkyl found that the lipid material that had been put into this chapter detracted from the main message halide must be used in the alkylation reaction.
Therefore, the lipid material was removed and put into a new chapter: The Organic Chemistry of Lipids. The 1. It is used so frequently by experienced synthetic chemists that itThe has book been given a name: retrosynthetic is designed to be modular,analysis. III—Chapters Typically, 15, 16, 17; the reagents needed Group IV—Chapters 18 andto carry 19 can out each stepinare be covered anynot specified until the reaction is written in the forward direction.
For example, the order. The spectroscopy chapters Chapters 13 and 14 are written so that they can be covered at any time during the course. Students are introduced to synthetic chemistry and retrosynthetic analysis early in the book www.
Seven special sections on synthesis design, each with a different focus, O are introduced at appropri- ate intervals. This edition has many new problems, both in-chapter and end-of-chapter. They include new solved problems, new problem- solving strategies, and new problems incorporating information from more than one chapter.
I keep a list of questions my students have when they come to office hours. Many of the new problems were created as a result of these questions. The problems within each chapter are primarily drill problems. They appear at the end of each section, so they allow students to test themselves on material just covered before moving on to the next section.
Short answers provided at the end of the book for problems marked with a diamond give students immediate feedback concerning their mastery of a skill or concept. Selected problems are accompanied by worked-out solutions to provide insight into problem- solving techniques, and the many Problem-Solving Strategies teach students how to approach vari- ous kinds of problems.
These strategies are followed by one or more problems that give students the oppor- tunity to use the strategy just learned. Powerpoint All the art in the text is available on PowerPoint slides.
I created the PowerPoint lectures so they would be consistent with the language and philosophy of the text. Students Interested in The Biological Sciences and Mcat I have long believed that students who take organic chemistry also should be exposed to bioorganic chemistry—the organic chemistry that occurs in biological systems.
Students leave their organic chemistry course with a solid appreciation of organic mechanism and synthesis. But when they take biochemistry, they will never hear about Claisen condensations, SN2 reactions, nucleophilic acyl substitution reactions, etc. Students should see that the organic reactions that chemists carry out in the laboratory are in many ways the same as those performed by nature inside a cell.
The seven chapters Chapters 20—26 that focus primarily on the organic chemistry of living systems emphasize the connection between the organic reactions that occur in the laboratory and those that occur in cells. For example, the first step in glycolysis is an SN2 reaction, the second step is identical to the enediol rearrangement that students learn when they study carbohydrate chemistry, the third step is another SN2 reaction, the fourth step is a reverse aldol addition, and so on.
The first step in the citric acid cycle is an aldol addition followed by a nucleophilic acyl substitution reaction, the second step is an E2 dehydration followed by the conjugate addition of water, the third step is oxidation of a secondary alcohol followed by decarboxylation of a 3-oxocarboxylate ion, and so on.
We teach students about halide and sulfonate leaving groups. Adding phosphate leaving groups takes little additional time but introduces the students to valuable information if they are going on to study biochemistry. But how many of these students are ever told that the reason for the difference in the bases in DNA and RNA is tautomerization and imine hydrolysis?
I found that tying together reactivity and synthesis see p. This is the organization I adopted many years ago when I was trying to figure out how to incorporate the bioorganic bridge into my course. The Bioorganic Bridge Bioorganic chemistry is found throughout the text to show students that organic chemistry and bio- chemistry are not separate entities but rather are closely related on a continuum of knowledge. Once students learn how, for example, electron delocalization, leaving-group propensity, electrophilicity, and nucleophilicity affect the reactions of simple organic compounds, they can appreciate how these same factors influence the reactions of organic compounds in cells.
Thus, the material is available to the curious student without requiring the instructor to introduce bioorganic topics into the course. For example, after hydrogen bonding is introduced in Chapter 3, hydrogen boding in proteins in DNA is discussed; after catalysis is intro- duced in Chapter 5, catalysis by enzymes is discussed; after the stereochemistry of organic reactions is presented in Chapter 6, the stereochemistry of enzyme-catalyzed reactions is discussed; after sulfonium ions are discussed in Chapter 10, a biological methylation reaction using a sulfonium ion is examined and the reason for the use of different methylating agents by chemists and cells is explained; after the methods chemists use to activate carboxylic acids are presented by giving them halide or anhydride leaving groups in Chapter 15, the methods cells use to activate these same acids are explained by giving them phosphoanhydride, pyrophosphate, or thiol leaving groups ; and after condensation reactions are discussed in Chapter 17, the mechanisms of some biological condensa- tion reactions are shown.
In addition, seven chapters in the last part of the book Chapters 20—26 focus on the organic chemistry of living systems. These chapters have the unique distinction of containing more chem- istry than is typically found in the corresponding parts of a biochemistry text. Chapter 22 Catalysis in Organic Reactions and in Enzymatic Reactions , for example, explains the various modes of catalysis employed in organic reactions and then shows that they are identical to the modes of catalysis found in reactions catalyzed by enzymes.
All of this is presented in a way that allows students to understand the lightning-fast rates of enzymatic reactions. Chapter 24 The Organic Chemistry of Metabolic www. Students also see that the synthesis of proteins in cells is just another example of a nucleophilic acyl substitution reaction. Thus, these chapters do not replicate what will be covered in a biochemistry course; they provide a bridge between the two disciplines, allowing students to see how the organic chemistry that they have learned is repeated in the biological world.
Every NADH studying by seeing Genetic engineering the genetic also called connections between modification a segment of DNAformed the ofreactions is the insertion into in a cell can result in the formation of 2. This means that the synthesis of thymine is energetically of ery organic of the host compounds that occur cell.
Genetic engineering in the has many laboratory practical applications. Cytosine eliminating the dependence on pigs for insulin and helping those who are allergic to pig insulin. Crops being produced withThe course. For example, genetically engineered For cotton example, crops are resistant we to theteach students cotton bollworm, about halide and genetically and engineered cornsul- is resistant to the deamination fonate leaving corn rootworm.
H H H Students who are studying organic chemistry learn about cytosine uracil Resisting Herbicides tautomerization and imine hydrolysis, and students study- amino tautomer imino tautomer ing biochemistry learn that DNA has thymine bases in place Glyphosate, the active ingredient in a well-known herbicide called Roundup, kills weeds by inhib- If a C in DNA is deaminated to a U, the U will specify incorporation of an A into the daughter iting an enzyme that plants need to synthesize phenylalanine and tryptophan, amino acids they strand during replication instead of the G that would have been specified by C, and all the progeny ofrequire the uracil bases for growth.
Corn in and RNA. Butbeen cotton have how manyengineered genetically of these students to tolerate the herbicide. Fortunately, there is an enzyme are ever told that the reason for the difference in the bases Then, when fields are sprayed with glyphosate, the weeds are killed but not the crops. The enzyme cuts out the U and replaces it with a C. If Us were. Unlike glyphosphate, normally N-acetylglyphosphate does not inhibit the enzyme that synthesizes phenylalanine and tryptophan. Now scientists are attempting to obtain drugs from plants by biopharming.
Biopharming uses genetic engineering techniques to produce drugs in crops such as corn, rice, tomatoes, and tobacco. R F R Cl R Br R I An experimental drug that was used to treat a handful alkyl fluoride of patients with Ebola, alkyl chloride the virus that was alkyl spread-bromide alkyl iodide ing throughout West Africa, was obtained from genetically engineered tobacco plants.
The tobacco plants were infected with three genetically engineered Alkyl halides plant virusesarethat a goodare family harmless of to compounds humans and withanimals which to start the study of substitution and elimination but have structures similar to that of the Ebola virus. Asreactions a resultbecause of beingthey have relatively infected, the plantsgood leaving groups; that is, the halide ions are produced antibodies to the viruses.
The antibodies wereeasily displaced. All 18 monkeys survived, whereas the three monkeysSubstitution in theand elimination control group died.
We will see, however, that because cells Currently, Five of the seven people given the drug survived. The Birth of the Environmental Movement Alkyl halides have been used as insecticides since , when it was discovered that DDT first www. It saved millions of lives, but no one realized at that time that, because it is a very stable compound, it is resistant to biodegradation. Therefore, they accumulate in the fatty tissues of birds and fish and can be passed up the food chain.
In , Rachel Carson, a marine biologist, published Silent Spring, where she pointed out the environmental impacts of the widespread use of DDT.
The book was widely read, so it brought the problem of environmental pollution to the attention of the general public for the first time. Consequently, its publication was an important event in the birth of the environmental movement. In , the Stockholm Convention banned the worldwide use of DDT except for the control of malaria in coun- tries where the disease is a major health problem.
Cl In Section It, too, can accumulate in the environment, however, so its use. Working through these problems will take only a little of your time. It will be time well spent, however, because curved arrows are used throughout the book and it is important that you are comfortable TUTORIAL with them. They provide covalent bonds form. The tail of the arrow is positioned where the electrons are in the reactant; the tail always starts at a lone pair or at a bond.
Thus, the arrow starts at the elec- trons that carbon and bromine share in the reactant, and the head of the arrow points at or as test preparation.
This is because it has lost the two electrons it was sharing with bromine. The bromine is negatively charged in the product because it has gained the electrons that it shared with carbon in the reactant. The fact that two electrons move in this example is indicated by the two barbs on the arrowhead.
Notice that the arrow always starts at a bond or at a lone pair. It does not start at a negative charge. The arrow starts at one of the lone pairs of the oxygen and points at the atom the carbon that will share the electrons in the product. The oxygen in the product is positively charged, because the electrons that oxygen had to itself in the reactant are now being shared with carbon. The carbon that was positively charged in the reactant is not charged in the product, because it has gained a share in a pair of electrons.
The answers to all problems appear immediately after Problem CH3 CH3 The average human body breaks down about 6 g of hemoglobin a. Then the bridge between the C and b. You can witness heme degradation by observing the changing colors of a bruise.
Some urobilinogen is trans- ported to the kidney, where it is oxidized to urobilin a yellow compound. This is the compound that gives urine its characteristic color.
If more bilirubin is formed than can be metabolized and excreted by the liver, it accumulates in the blood. When its concentration there reaches a certain level, it diffuses into the tissues, giving them a yellow appearance.
This condition is known as jaundice. O quaternary ammonium www. O sulfonium reactions, nucleophilic addi- sulfonate salt from an A-carbon forms a nucleophile that can They undergo electrophilic aromatic substitution tion reactions, and nucleo- ester react with electrophiles. Halo-substituted benzenes reactions They undergo nucleophilic and halo-substituted pyridines are electrophiles. All the compounds in Group IV are aromatic. To preserve the aromaticity of the rings, these.
Follow-up problems that require What is the product of the reaction of acetyl chloride with CH3O-? These To identify the product of the reaction, we need to compare the basicities of the two groups in the tetra- Starting with methyl propanoate, how could you prepare 4-methylheptanone?
The Claisen methyl condensation forms a acetate b-keto ester that can be easily alkylated at the desired carbon because it is flanked by two carbonyl groups. Acid-catalyzed hydrolysis forms a 3-oxocarboxylic acid that decarboxylates when heated. What is the product of the reaction O chloride with HO-? What is2. CH3product O of the reaction of acetamide with1. Many problems bond to produce two fragments. For example, an ester carbonyl group would be a good electrophile for this synthesis because it has a group that would be eliminated.
Moreover, the a-hydrogens of the ketone are more acidic than the a-hydrogens of the ester, so the desired nucleophile would be easy to obtain.
Thus, converting the starting material to an ester Section SOCl2 H3C 1. The text works with MasteringChemistry to guide students on what they need to know before testing them on the content.
The third edition continually engages students through pre-lecture, during- lecture, and post-lecture activities that all include real-life applications. Now assignable, Dynamic Study Modules enable your students to study on their own and be better prepared for class.
The modules cover content and skills needed to succeed in organic chemistry: fundamental concepts from general chemistry; practice with nomenclature, functional groups, and key mechanisms; and problem-solving skills.
For students who want to study on the go, a mobile app that records student results to the MasteringChemistry gradebook is available for iOS and Android devices. Spectroscopy Simulations www. Activities authored by Mike Huggins, University of West Florida, prompt students to utilize the spectral simulator and walk them through different analyses and possible conclusions. The first presentation contains the images embedded within PowerPoint slides.
The second includes a complete lecture outline that is modifiable by the user. Powerpoints of the in-chapter worked examples are also included. In addition, you will find additional spectroscopy problems.
This Solutions Manual provides detailed solutions to all in- chapter, as well as end-of-chapter, exercises in the text. In particular, a loud thanks goes to Richard Morrison of the University of Georgia, who read every page, made critically important suggestions, checked every answer in the Solutions Manual, and created many new end-of-chapter problems—and to Jordan Fantini of Dennison University, who created the interactive digital modules designed to engage students in the fundamental principles of reactivity while advancing their visualization skills.
I also thank my many students, who pointed out sections that needed clarification, searched for errors, and whose questions guided the creation of new problems. The following reviewers have played an enormously important role in the development of this book.
Eighth Edition Contributors Benjamin W. Sessions, Valencia College Richard J. Louis Harold R. I am also extremely grateful to have had the opportunity to work with Matt Walker, the development editor.
I am also grateful to Elisa Mandelbaum, the project editor, whose attention to detail and creation of manageable deadlines made the book actually happen. And I want to thank the other talented and dedicated people at Pearson whose contributions made this book a reality: I particularly want to thank the many wonderful and talented students I have had over the years, who inspired me, challenged me, and who taught me how to be a teacher.
And I want to thank my children, from whom I may have learned the most. To make this textbook as user friendly as possible, I would appreciate any comments that will help me achieve this goal in future editions. If you find sections that could be clarified or expanded, or examples that could be added, please let me know. Finally, this edition has been painstakingly combed for typographical errors. Any that remain are my responsibility.
If you find any, please send me a quick email so they can be corrected in future printings of this edition. Her research interests center on the mechanism and catalysis of organic reactions, particularly those of biological significance. Paula has a daughter and a son who are physicians and a son who is a lawyer.
PART An Introduction to the ONE Study of Organic Chemistry The first three chapters of this textbook cover a variety of topics with which you need to be familiar to start your study of the reactions and synthesis of organic compounds.
The chapter starts with a description of the structure of atoms and then proceeds to a description of the structure of molecules. Molecular orbital theory is introduced. You will see how the structure of a molecule affects its acidity and how the acidity of a solution affects molecular structure. In Chapter 3, you will learn how to name five differ- ent families of organic compounds. This will give you a good understanding of the basic rules for naming compounds. Because the compounds examined in the chapter are the reactants or the prod- ucts of many of the reactions presented in the first third of the book, you will have numerous oppor- tunities to review the nomenclature of these compounds as you proceed through these chapters.
Chapter 3 also compares and contrasts the structures and physical properties of these compounds, which makes learning about them a little easier than if the structure and physical properties of each family were presented separately.
Because organic chemistry is a study of compounds that contain carbon, the last part of Chapter 3 discusses the spatial arrangement of the atoms in both chains and rings of carbon atoms. Compounds derived mentioned in this text book can from living organisms were believed to contain an immeasurable vital force—the essence of life.
Why is an entire branch of chemistry devoted to the study of carbon-containing compounds? We study organic chemistry because just about all of the compounds that make life possible and that make us who we are—proteins, enzymes, vitamins, lipids, carbohydrates, DNA, RNA—are organic compounds.
Thus, the chemical reactions that take place in living systems, including our 2. Most of the compounds found in nature—those that we rely on for food, clothing cotton, wool, silk , and energy natural gas, petroleum —are organic compounds as well.
Organic compounds are not limited to those found in nature. Chemists have learned how to synthesize millions of organic compounds not found in nature, including synthetic fabrics, plastics, synthetic rubber, and even things such as compact discs and Super Glue. And most importantly, almost all commonly prescribed drugs are synthetic organic compounds.
Some synthetic organic compounds prevent shortages of naturally occurring compounds. For example, it has been estimated that if synthetic materials—nylon, polyester, Lycra—were not avail- able for clothing, all of the arable land in the United States would have to be used for the production of cotton and wool just to provide enough material to clothe us. Other synthetic organic compounds provide us with materials we would not have—Teflon, Plexiglas, Kevlar—if we had only naturally occurring organic compounds.
Currently, there are about 16 million known organic compounds, and many more are possible that we cannot even imagine today. Why are there so many carbon-containing compounds? Carbon is in the center of the second row of elements. We will see that the atoms to the left of carbon have a tendency to give up electrons, whereas the atoms to the right have a tendency to accept electrons Section 1.
Instead, it shares electrons. Carbon can share electrons with several kinds of atoms as well as with other carbon atoms. Consequently, carbon forms millions of stable compounds with a wide range of chemical properties simply by sharing electrons.
Natural Versus Synthetic Organic Compounds It is a popular belief that natural substances—those made in nature—are superior to synthetic ones—those made in the laboratory. Some- times chemists can even improve on nature. Most commercial morphine is obtained from opium, the juice extracted from the species of poppy shown in the photo.
Morphine is the starting material for the synthesis of heroin. Organic compounds consist of atoms held together by covalent bonds. When an organic compound reacts, some of these covalent bonds break and some new covalent bonds form. Covalent bonds form when two atoms share electrons, and they break when two atoms no longer share electrons. How easily a covalent bond forms or breaks depends on the electrons that are shared, which, in turn, depends on the atoms to which the electrons belong.
So if we are going to start our study of organic chemistry at the beginning, we must start with an understanding of the structure of an atom—what electrons an atom has and where they are located. The nucleus contains positively charged protons and uncharged neutrons. The electrons are negatively charged. The amount of positive charge on a proton equals the amount of nega- The electrons are tive charge on an electron. Therefore, the number of protons and the number of electrons in an negatively charged.
Electrons move continuously. Protons and neutrons have approximately the same mass and are about times more massive than an electron. Most of the mass of an atom, therefore, is in its nucleus.
Most of the volume of an atom, however, is occupied by its electron cloud. This is where our focus will be because it is the electrons that form chemical bonds. The atomic number of an atom is the number of protons in its nucleus. The atomic number is unique to a particular element. For example, the atomic number of carbon is 6, which means that all uncharged carbon atoms have six protons and six electrons. Although atoms can gain electrons and become negatively charged or lose electrons and become positively charged, the number of protons in an atom of a particular element never changes.
The mass number of an atom is the sum of its protons and neutrons. Although all carbon atoms have the same atomic number, they do not all have the same mass number. Because carbon atoms can have varying numbers of neutrons. For example, These two different kinds of carbon atoms 12C and 13C are called isotopes. This isotope of carbon is radioactive, decaying with a half-life of years. The half-life is the time it takes for one-half of the nuclei to decay.
As long as a plant or an animal is alive, the 14C that is lost through exhalation or excretion is constantly replenished. Consequently, its 14C is slowly lost through radioactive decay. Therefore, the age of a substance derived from a living organism can be determined by its 14C content.
Therefore, the atomic mass of carbon is The molecular mass is the sum of the atomic masses of all the atoms held together by bonds. The atomic number of oxygen is 8. How many protons and neutrons does each of the isotopes have?
How many protons do the following species have? See the periodic table inside the back cover of this book. How many electrons does each have? The atomic mass of 35Cl is What is the atomic weight of chlorine?
Albert Einstein 1. In , however, Louis de Broglie, a French physicist, showed that electrons three most important contributions to science: the photoelectric effect, the equivalency of also have wave-like properties.
He did this by combining a formula developed by Albert Einstein energy and matter, and the theory of relativity. At his feet is a map of the sky. The realization that electrons have wave-like properties spurred physicists to propose a math- ematical concept known as quantum mechanics to describe the motion of an electron around a nucleus.
Quantum mechanics uses the same mathematical equations that describe the wave motion of a guitar string to characterize the motion of an electron around a nucleus.
Table 1. The second shell lies farther from the nucleus. The third and higher numbered shells lie even farther out. We will see that an atomic orbital has a characteristic shape and energy and occupies a characteristic volume of space Section 1. Each second and higher shell—in addition to its s atomic orbital—contains three degenerate p atomic orbitals. Degenerate orbitals are orbitals Degenerate orbitals are orbitals that have the same energy.
The third and higher shells—in addition to their s and p atomic that have the same energy. See the Pauli exclusion principle on p. Therefore, the first four shells, with 1, 4, 9, and 16 atomic orbitals, respectively, can contain a maximum of 2, 8, 18, and 32 electrons. In our study of organic chemistry, we will be concerned primarily with atoms that have electrons only in the first two shells.
If energy is applied to an atom in the ground state, one or more electrons can jump into a higher-energy orbital. The atom then would be in an excited state and have an excited-state electronic configuration. The ground-state electronic configurations of the smallest atoms are shown in Table 1.
Each arrow—whether pointing up or down—represents one electron. When using the aufbau principle rule, it is important to remember that the closer the atomic orbital is to the nucleus, the lower is its energy. Because the 1s orbital is closer to the nucleus, it is lower in energy than the 2s orbital, which is lower in energy—and closer to the nucleus—than the 3s orbital.
When comparing atomic orbitals in the same shell, we see that an s orbital is lower in energy than a p orbital, and a p orbital is lower in energy than a d orbital. The Pauli exclusion principle states that no more than two electrons can occupy each atomic orbital, and the two electrons must be of opposite spin.
This is called an exclusion principle because it limits the number of electrons that can occupy www. Notice in Table 1. These first two rules allow us to assign electrons to atomic orbitals for atoms that contain one, two, three, four, or five electrons. The subscripts x, y, and z distinguish the three 2p orbitals. Because the three p orbitals are degenerate, the electron can be put into any one of them. Before we can discuss atoms containing six or more electrons, we need the third rule. In this way, electron repulsion is minimized.
The locations of the electrons in the remaining elements can be assigned using these three rules. Valence and Core Electrons The major factor that determines the chemical behavior of an element is the number of valence electrons Valence electrons are electrons it has.
Electrons in inner shells below the in the outermost shell. For example, carbon has four valence electrons and two core electrons Table 1. Valence electrons participate in chemical bonding; core electrons do not. Core electrons are electrons in inner shells. Elements in the same column of the periodic table have similar chemical properties because they have the same number of valence electrons. If you examine the periodic table inside the back cover The chemical behavior of of this book, you will see that lithium and sodium, which have similar chemical properties, are in an element depends on its the same column because each has one valence electron.
Write the ground-state electronic configuration for chlorine atomic number 17 , bromine atomic number 35 , and iodine atomic number How many valence electrons do chlorine, bromine, and iodine have? How many core electrons does each have? How many valence electrons does each have? In explaining why atoms form bonds, G. Lewis proposed that an atom is most stable if its outer shell is either filled or contains eight electrons, and it has no electrons of higher energy.
This theory has come to be called the octet rule even though hydrogen needs only two electrons to achieve a filled outer shell. If it loses this electron, lithium ends up with a filled outer shell—a stable configuration. Lithium, therefore, loses an electron relatively easily. Sodium Na has a single electron in its 3s orbital; so it, too, loses an electron easily.
The symbol for the element represents the protons, neutrons, and core electrons. Each valence electron is shown as a dot. When the single valence electron of lithium or sodium is removed, the species that is formed is called an ion because it carries a charge. Fluorine has seven valence electrons Table 1. Therefore, it readily acquires an electron to fill its outer shell. Gaining the electron forms F - , a fluoride ion. A hydrogen atom has one valence electron.
Therefore, it can achieve a completely empty shell by losing an electron, or a filled outer shell by gaining an electron. A positively charged hydrogen ion is called a proton because when a hydrogen atom loses its valence electron, only the hydrogen nucleus—which consists of a single proton—remains.
When a hydrogen atom gains an electron, a negatively charged hydrogen ion—called a hydride ion—is formed.
Find potassium K in the periodic table and predict how many valence electrons it has. What orbital does the unpaired electron occupy? For example, two fluorine atoms can each attain a filled second shell by sharing their unpaired valence electrons.
A bond formed as a result of sharing electrons between two nuclei is called a covalent bond. A covalent bond is commonly shown by a solid line rather than by a pair of dots. Oxygen has six valence elec- trons, so it needs to form two covalent bonds to achieve an outer shell of eight electrons. Nitrogen, with five valence electrons, must form three covalent bonds, and carbon, with four valence elec- trons, must form four covalent bonds.
Notice that all the atoms in water, ammonia, and methane have filled outer shells. Electronegativity is a measure of the ability of an atom to the same electronegativity. The electronegativities of some of the elements are shown in Table 1. A polar covalent bond is Notice that electronegativity increases from left to right across a row of the periodic table and from a covalent bond between atoms bottom to top in any of the columns. As a result, there are several scales of electronegativities.
The electronegativities listed here are from the scale devised by Linus Pauling. If the electronegativity difference between the bonded atoms is less than 0. That is, the atoms share the bonding electrons equally—the electrons represented by the bond are symmetrically distributed around each atom. Examples of nonpolar covalent bonds are shown below. The negative end of the sodium chloride crystals table salt bond is the end with the more electronegative atom.
The greater the difference in electronegativity between the bonded atoms, the more polar the bond. By convention, chemists draw the www.
Thus, the head of the arrow is at the negative end of the bond; a short perpendicular line near the tail of the arrow marks the positive end of the bond. Physicists draw the arrow in the opposite direction. Lithium If the electronegativity difference between the atoms is greater than 1.
Sodium chloride is an example of an ionic compound also known as a salt. Ionic disorder. Scientists do not yet know why compounds are formed when an element on the left side of the periodic table transfers one or more lithium salts have these therapeutic effects. Polar covalent bonds fall somewhere in between. The size of the dipole is indicated by the dipole moment. Because the charge on an electron is 4.
Thus, a dipole moment of 1. The dipole moments of bonds commonly found in organic compounds are listed in Table 1. For example, the dipole moment of hydrogen chloride HCl is 1. The dipole moment of a molecule with more than one covalent bond depends on the dipole moments of all the bonds in the molecule and the geometry of the molecule.
We will look at this in Section 1. Because oxygen is more electronegative than carbon, oxygen has a partial negative charge and carbon has a partial positive charge. H 3Cd. The bond length is 1. The charge on an electron is 4. Red, signifying the most negative electrostatic potential, is used for regions that attract electron-deficient species most strongly. Because the angstrom continues to be used by many organic chemists, we will use angstroms in this text book.
Other colors indicate interme- diate levels of attraction. By comparing the three maps, we can tell that the hydrogen in LiH is more electron- rich than a hydrogen in H2, whereas the hydrogen in HF is less electron-rich than a hydrogen in H2. A particular atom can have different sizes in different molecules, because the size of an atom in a potential map depends on its electron density.
For example, the negatively charged hydrogen in LiH is bigger than a neutral hydrogen in H2, which is bigger than the positively charged hydrogen in HF. Which compounds are polar? Why does LiH have the largest hydrogen? Which compound has the hydrogen that would be most apt to attract a negatively charged molecule?
Then we will look at the kinds of structures that are used more commonly for organic compounds. Lewis Structures The chemical symbols we have been using, in which the valence electrons are represented as dots or solid lines, are called Lewis structures. Lewis structures show us which atoms are bonded together and tell us whether any atoms possess lone-pair electrons or have a formal charge, two concepts described below.
Therefore, www. Lone-Pair Electrons When you draw a Lewis structure, make sure hydrogen atoms are surrounded by two electrons and Lone-pair electrons are valence C, O, N, and halogen F, Cl, Br, I atoms are surrounded by eight electrons, in accordance with electrons that do not form bonds. Valence electrons not used in bonding are called nonbonding electrons, lone-pair electrons, or simply, lone pairs.
Formal Charge Once the atoms and the electrons are in place, you must examine each atom to see whether a formal charge should be assigned to it. Notice that half the bonding electrons is the same as the number of bonds.
An oxygen atom has six valence electrons Table 1. Notice that one-half of the bonding electrons is the same as the number of bonds. Which atom bears the formal negative charge in the hydroxide ion? Which atom has the greater electron density in the hydroxide ion? Which atom bears the formal positive charge in the hydronium ion? Which atom has the least electron density in the hydronium ion?
Drawing Lewis Structures Nitrogen has five valence electrons Table 1. Recall that a cation is a positively charged ion and an anion is a negatively charged ion. A species containing an atom with a single unpaired A carbanion is a species electron is called a radical often called a free radical. CH3 O CH3 b. These numbers are very important to remember when you are drawing structures of organic compounds because they provide a quick way to recognize when you have made a mistake.
Atoms with more bonds or fewer bonds than is required for a neutral atom must have either a formal charge or an unpaired electron.
Each atom in the following Lewis structures has a filled outer shell. Notice that because none of the molecules has a formal charge or an unpaired electron, H forms 1 bond, C forms 4 bonds, N forms 3 bonds, O forms 2 bonds, and Br forms 1 bond.
Notice, too, that each N has 1 lone pair, each O has 2 lone pairs, and Br has 3 lone pairs. Draw the Lewis structure for CH4O. Draw the Lewis structure for HNO2. Distribute the atoms, remembering that C forms 4 bonds, O forms 2 bonds, and each H forms 1 bond. Always put the hydrogens on the outside of the molecule because H can form only 1 bond. F orm bonds and fill octets with lone-pair electrons, using the number of valence electrons determined in 1.
A ssign a formal charge to any atom whose number of valence electrons is not equal to the number of its lone-pair electrons plus the number of bonds. None of the atoms in CH4O has a formal charge. Distribute the atoms, putting the hydrogen on the outside of the molecule.
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