How To Study Chemistry

Page 1

Contents This table of contents is a handy checklist of many of the suggestions given in this book for the study of chemistry. Section Keep this little book handy and refer to it often. Know the makeup of your chemistry course. Maintain an alert mind and cheerful attitude. Apply what you learn to the world around you . The essence of studying chemistry-have faith, study hard, think. Study frequently and do problems. Ask questions and get help from your instructor. Get help from a tutor. Alleviate anxiety. Refine your understanding of topics through repetitive study. Learn chemistry by writing. Learn the bread and butter stuff well. Learn the language of chemistry. Memorize selected material. Progress from the simple to the complex. Explain things and learn generalizations. Study your textbook with the full force of your intellect. Study the chapter prior to attending lectures on it and keep good lecture notes. Correlate material for better understanding and retention. Distinguish between related items to increase your mental acuity. Learn basic mathematics and solve many problems of all types. Use the periodic table for learning the physical and chemical properties of the elements. Learn general reactions and illustrate each general reaction with specific examples. Organic chemistry : memorize types of organic compounds and types of organic reactions. Study biochemistry like organic chemistry and learn metabolic pathways. Study for tests well in advance. Try to study when sickness strikes. Introduction to sample ancillary pages.

Page 2 This little book gives realistic suggestions on how to study college general chemistry and high school chemistry. You may find that some of the suggestions are also beneficial for the study of other subjects. Keep this little book handy and refer to it often. Read and reread this little book, again and again, during the course of your study. Most suggestions given herein apply to all phases of your study; some suggestions, however, apply only to certain areas of your study. In any case, refer to this little book often; it was written to help you in your study of chemistry. Keep it handy; tuck it in your textbook or in your lecture notebook. My hope is that you will put these suggestions into practice and that you will be successful in your study of chemistry. Know the makeup of your chemistry course. The content of a general chemistry course is taken from five traditional branches of chemistry - inorganic, organic, physical, analytical, and biochemistry. General chemistry courses vary in content. For example, in a course suited for allied health students, the first semester is devoted to the study of inorganic chemistry and elementary physical chemistry, while nearly all of the second semester is devoted to organic chemistry and biochemistry. In a more traditional course, the proportion of organic chemistry and biochemistry is much less, while the proportion of inorganic and physical chemistry is correspondingly greater. Inorganic chemistry involves the study of the structure and chemical reactions of substances composed of any of the known elements. The study of compounds of carbon is so vast that it occupies a separate branch of chemistry called organic chemistry. Biochemistry deals with the study of the chemical structure of living material and of the chemical reactions occurring in living cells. Physical chemistry involves the application of quantitative and mathematical methods to the solution of chemical problems. Analytical chemistry is concerned with the qualitative and quantitative analysis of substances by physical and chemical methods. Get a bird's eye view of your chemistry course at the very start of it. Look over the topics given in the syllabus handed to you at the beginning of the course by your instructor. Look over the topics given in the table of contents of your textbook. Read the preface of your textbook for enlightening remarks on the makeup of your textbook. Thumb through your textbook. Stop here and there and spot-read. Take note of learning objectives, tables, graphs, marginal notes, word lists, summaries, and problems. Maintain an alert mind and cheerful attitude. Intellectual effort is best served by a well-nourished and well-rested body. Rest on your day of rest; take delight in the banquet of life. Renew yourself spiritually. Treat yourself to pizza or stuffed cabbage or chicken paprika. Engage in physical activity regularly; it tones up the mind as well as the body. By attending to your needs, you ensure an alert mind and cheerful attitude, both of which are conducive to learning chemistry. Apply what you learn to the world around you. Enliven your interest in chemistry by relating what you learn to everyday things and occurrences. Our world is a chemical world. To learn chemistry is to learn about the world we live in. Consider a few ways in which chemistry is involved in our lives. Food production worldwide has increased through the use of fertilizers. Commercial fertilizers contain such inorganic compounds as ammonium nitrate, ammonium sulfate, calcium dihydrogen phosphate, calcium sulfate, and potassium chloride. Ammonia gas also is applied directly to the soil to provide nitrogen for the plants. Environmental pollution is largely a chemical problem. Consider formation of acid rain. When fuels containing sulfur are burned, sulfur dioxide and sulfur trioxide are formed and escape into the atmosphere. Moisture and rain react with these compounds to form sulfurous and sulfuric acids. These acids pollute the air and fall to the earth where they adversely affect vegetation. Chemists and others are actively seeking ways to reduce and prevent pollution of our environment. Synthetic fibers, such as nylon and polyesters, are used in the manufacture of clothing. Nylon and polyesters are giant organic molecules called polymers. A polymer is manufactured from one or two simple chemical compounds called monomers. Polyethylene, a polymer made from ethylene, is used in the manufacture of storage bags and of other plastic ware. Today, research in biochemistry is being vigorously pursued. Biochemists have discovered that the disease phenylketonuria (PKU) in the newborn is a genetic disease. In this disease, the gene for directing the synthesis of the enzyme phenylalanine hydroxylase is defective; therefore, this enzyme is not produced. Without this enzyme, the amino acid phenylalanine cannot undergo its normal conversion to another amino acid, tyrosine. Instead, some of the excess phenylalanine is converted to the end-product phenylpyruvate. Both phenylalanine and phenylpyruvate build up in the system, causing severe mental retardation. PKU is detected in the newborn by a simple urine test. If PKU is present, the child is put on a low phenylalanine diet until the brain is completely formed. Many more applications of chemistry will be found in your textbook and will be discussed by your lecturer. In addition, newspaper and magazine articles and radio and television programs are good sources of knowledge about our chemical world. Relating what you learn to practical things and occurrences not only increases your interest in chemistry but also helps you retain what you learn. Consumer chemistry is a popular college course. As the title of the course indicates, practical aspects of chemistry are studied. No prior knowledge of chemistry is needed to take a course of this type. In fact, only a minimal amount of chemistry is presented in the course, just enough to indicate, superficially, the chemical nature of things and occurrences. This course in not equivalent to a regular general chemistry course.

Page 3 The essence of studying chemistry-have faith, study hard, think. You may be a very good student but yet you may encounter difficulty in learning chemistry. Why is this so ? The reasons seem to be that the study of chemistry requires new attitudes, new approaches, new modes of thinking, and new study habits not used in non-scientific courses. The teaching and learning of chemistry are acts of faith. You must have faith in your teacher-faith in his ability to prepare his lectures well and to present them in an organized and lucid manner. You must have faith in yourself-faith in your ability to learn from your teacher and from your textbook. This faith in yourself must be translated into real intellectual effort. You must be willing to accept the academic challenge. Learning chemistry is hard work and takes time. Learning chemistry is an active pursuit that requires concentration, discipline, patience, persistence, and practice. To be concentrated means to devote full attention to the task at hand while blocking out the many things that cause distraction. To be disciplined means to plan your study time and to keep to your plan of study. Do not take shortcuts. Stay with the methods that work best for all of us : be disciplined, concentrate, be persistent, practice much, study hard. These are the ways that ensure success in the study of chemistry. Think. To think means to meditate; to reflect upon; to consider a matter; to imagine; to reason; to determine a solution to a difficulty; to exercise powers of judgment, conception, or inference; to reflect for the purpose of reaching a conclusion; to have or form a mental picture. To be successful in the study of chemistry you must think. Study frequently and do problems. Try to study chemistry nearly every day. Make problem solving a part of every study session. Study by yourself most of the time. You may follow-up your independent study by studying with a friend. Occasionally, studying in a small group may be beneficial, provided that you do your own studying beforehand. One student of the group may act as lecturer, presenting and discussing the material while other students contribute information from time to time. Then the roles may be reversed. Ask questions and get help from your instructor. Be curious. Ask questions during lecture. Specific questions are best. Avoid asking broad questions in class. Reserve broad questions for a private meeting with your instructor. After class, seek help and advice from your instructor. Go to him or her as often as needed. Prepare in advance a list of questions to be asked and problems to be solved. Get help from a tutor. You may choose to engage the services of a private tutor. If you do, prepare for each tutoring session by studying the work to be reviewed and by making a list of topics to be discussed, questions to be asked, and problems to be solved. Prior preparation will ensure efficient use of time. Note that a typical numerical problem takes about ten minutes to work out and discuss. During the session the tutor will record notes that will be given to you at the end of the session. Additionally, you may record the commentary on a cassette tape. As soon as possible after the tutoring session, review the notes and listen to the tape; correlate them with companion textbook material and lecture notes. You are the one to decide the frequency of tutoring sessions. Your decision will be dictated by how much you benefit from each session, the difficulty of new work, and the need for test preparation. Alleviate anxiety. Most scientific textbooks look formidable. The size and, more so, the content of your new chemistry textbook may cause you to generate fear and anxiety, particularly so if you did not take chemistry in high school or if you think that you are not scientifically-minded. You might ask-how could I hope to learn all this ? The cliché first-things-first seems appropriate here. General chemistry is presented in a logical manner-the simpler methods and concepts preceded the more complex ones. You gradually build upon existing knowledge at each stage of your study. This manner of learning chemistry requires that you keep abreast of the lecturing by attending all lectures and by studying chemistry nearly every day. As you learn more and more, your chemical intuition and confidence increase. Refine your understanding of topics through repetitive study. Repetition is necessary for learning chemistry. Few students are so expert that they can learn it all the first time around. That your study requires considerable repetition is not a sign of your inadequacy but is a necessary method for learning chemistry. With a critical mind, go over the material again and again. Each time you do so, you refine your understanding of the topic. Through repetitive study many facts, concepts, and methods will be committed to memory. Much will become second nature to you. Learn chemistry by writing. The ability to write well is advantageous in school and on the job. Writing is a good way to learn chemistry. The act of writing makes you think. When studying chemistry, retell the story of what you learn in your own words. Write out descriptions, explanations, and interpretations in clear, concise, and specific language, giving examples where appropriate. Write and rewrite until the picture is clear and concise. This practice also will benefit you in tests. Tests may include questions that require brief descriptions or explanations. A clear, concise, and accurate answer will save time and earn full credit. A valuable little book on rhetoric is W. Strunk, Jr., and E. B. White, The Elements of Style, The Macmillan Co., NY. Borrow a copy from the library or buy one. It comes in hardback and paper copies. The paper copy is much cheaper; it costs about three dollars. The book is in its third edition, but an earlier edition will do. Some of the rules of rhetoric given in this book

Page 4 are : put statements in positive form; use definite, specific, concrete language; omit needless words, avoid a succession of loose sentences; use orthodox spelling; avoid fancy words; be clear; do not take shortcuts at the expense of clarity. Learn the bread and butter stuff well. A significant portion of what you learn early in the course is very fundamental and is used repeatedly during the remainder of the course. A partial list of these items is : – – – – – – – – –

metric system (length and especially mass and volume) significant figures exponential numbers factor-label method (also called dimensional analysis) simple algebra temperature (Fahrenheit, Celsius, Kelvin) chemical symbols and names of about 40 commonly used elements chemical symbols (formulas) and names of commonly used simple and polyatomic ions writing and naming chemical formulas of ionic and molecular substances

Items such as these are bread and butter stuff. Through repeated practice learn them so well that they become second nature to you. Learn the language of chemistry. Learn and use the vocabulary of chemistry. Learn definitions of words. Key words are usually given in boldface print within the chapter. Almost always a word list is found at the end of the chapter. Write definitions of these words; give an example or two where appropriate. If definitions are given along with the words, then rewrite the definition in your own words. Recite to yourself the definitions you have written. Review the word list from time to time. If a glossary is given at the back of your textbook, consult it as you study. Use the eye and the ear to learn the vocabulary of chemistry. Chemistry is a science of symbolism. The elements, the ions, ionic and molecular substances, and chemical equations are written and expressed in chemical symbols. Learn and practice using the symbols of chemistry. Examples of chemical symbolism are given below : Symbolism H H2 O O2 Mg O2Mg2+ MgO H2O

What the chemical symbolism means the element hydrogen or an atom of hydrogen a diatomic molecule of hydrogen the element oxygen or an atom of oxygen a diatomic molecule of oxygen the element magnesium or an atom of magnesium oxide ion magnesium ion chemical formula of the ionic compound magnesium oxide; this compound is composed of magnesium ions and oxide ions chemical formula of the molecular compound water; each molecule of water is composed of two hydrogen atoms bonded to an oxygen atom

Magnesium reacts vigorously with oxygen to produce magnesium oxide. The chemical equation for this reaction is : 2 Mg + O2 → MgO This reaction, which gives off heat and light, is the familiar flashbulb reaction. Passage of electricity through water (electrolysis of water) causes water to decompose, producing hydrogen gas and oxygen gas. The chemical equation for this reaction is : 2 H2O   → 2 H2 + O2 electriccurrent

Nomenclature and chemical symbolism go hand in hand. Learn to name a chemical substance when given its chemical symbol or chemical formula. Learn to write the chemical symbol or chemical formula of a substance when given its chemical name. Most textbooks contain a chapter on chemical nomenclature. Learn this chapter well. Learn and practice writing chemical symbols and formulas of substances, together with the corresponding names, at every opportunity as you study chapter after chapter.

Page 5 Memorize selected material. Memorization plays a significant role in learning chemistry. Much is memorized through repetitive study. Memorized facts serve as fuel for running the machinery of one's mind. Memorize, for example, the chemical symbols and names of about 40 commonly used elements. Of these elements, the commonly used nonmetals are carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur, fluorine, chlorine, bromine, iodine, and the noble gases helium, neon, argon, krypton, xenon, and radon. All of the other elements commonly used are metals; a few are metalloids. Progress from the simple to the compl ex. An example of how your knowledge and expertise will progress during the course from a simple stage to a more complex one is given here. Suppose your problem is to write the chemical equation for the reaction occurring between magnesium nitrate and sodium hydroxide in aqueous solution. What must you learn that will enable you to write this equation with confidence ? In what order will you learn the material ? First you must learn chemical symbols of elements. Then you must learn chemical symbols and formulas of simple and polyatomic ions. Next you must learn how to write chemical formulas of ionic compounds. Finally, you must learn how to write and balance chemical reactions. This knowledge and expertise will enable you to write the equation for the reaction occurring between magnesium nitrate and sodium hydroxide in aqueous solution. The equation is : Mg(NO3)2 + magnesium nitrate

2 NaOH sodium hydroxide

→ Mg(OH) 2 + magnesium hydroxide

2 NaNO3 sodium nitrate

You also will be able to write the net ionic equation for the reaction : Mg2+ + magnesium ion

2 OHhydroxide ion

→ Mg(OH) 2 magnesium hydroxide

The sequence of topics involved in this example is : element → simple and polyatomic ions → ionic compounds → chemical equations → net ionic equations This sequence of topics illustrates just one line of continuity in the study of chemistry. The topics are studied in a logical sequence and then the topics are put together to achieve a goal. In this example, the goal is to be able to write the chemical equation for the reaction occurring between ionic substances. Be aware of the cumulative nature of chemistry. In many instances new work can be understood only after earlier work has been learned well. Progress from the simple to the complex by building upon existing knowledge at each stage of your study. Tie topics together wherever possible; that is, formulate lines of continuity in the subject matter. Express each line of continuity in the form of a sequential chart of related topics, as illustrated above. Explain things and learn generalizations. Chemistry is an experimental science. The facts obtained from experiments are organized and analyzed. What do the facts mean ? One or more explanations may be offered. To explain something means to translate the unfamiliar into the familiar. In your study of chemistry, learn to do just that-learn to explain things, to translate what is unfamiliar into familiar and readily understandable terms. In this respect, pay close attention to the language used in your textbook and by your lecturer when explanations are offered. Capture the line of reasoning. Practice writing explanations wherever possible; rewrite, if necessary, to make your explanations clear and concise. Recite explanations to yourself. Explain things to your study partner or to your pet dog or pet cat. Learn generalizations. When a researcher recognizes a regularity or general trend in data obtained through experimentation, he formulates a statement called a generalization. Generalizations, once stated, are useful for explaining chemical phenomena and for predicting new relationships and new facts that may be verified by experimentation. Be cautious. Chemistry is not an exact science. Expressions such as "approximately, " "generally, " and "essentially, " used in the textbook and by your lecturer, reflect the inexactness of chemistry, in general, and the exceptions to generalizations, in particular.

Page 6 Study your textbook with the full force of your intellect. At the first meeting of the class the instructor will hand out a syllabus giving lecture dates, topics to be covered (chapter titles), and suggested exercises. The syllabus also will define attendance and grading policies. In your textbook, check off assigned exercises. Note and mark chapters or sections of chapters that are to be omitted. Note the sequence of chapters to be covered; not all instructors follow the numerical sequence given in the textbook. Prior to the first lecture of the course, look over your textbook so that you get a bird's eye view of its contents. Read the preface and any special note to the student. Look over the appendices. Study the appendix on basic mathematics if you are rusty in fundamental operations. Carefully look over the table of contents; note titles of chapters and subheadings. Within the book, note whether or not learning objectives are given at the beginning of the chapter. Read these objectives prior to and after studying the chapter. Note exercises with solutions given within the body of the chapter. Pay attention to marginal notes, graphs, tables, and charts. At the end of each chapter, inspect the word list, summary, and exercises. Some textbooks give references at the end of each chapter or at the back of the book. Consult these from time to time. College and university libraries have good collections of chemistry books and journals. Today, most chemistry textbooks have a companion study guide that gives answers to exercises, worked out solutions to numerical problems, and other useful information. Buy a copy of the study guide; it's money worth spending. Prior to a detailed study of a chapter, first take a quick look at its contents. Read the learning objectives, note titles of topics, look over the word list, and read the summary. This quick view of the chapter will tell you where you are heading. Then make a careful and detailed study of the chapter. Apply methods of study outlined in this book. Dissect paragraphs, even sentences. Attack the material with the full force of your intellect. Study with your heart as well as with your mind. Use the index to find all possible information in your textbook on a particular topic. You will discover that, in some cases, material given in a later chapter is useful for understanding current work. Study the chapter prior to attending lectures on it and keep good lecture notes. Study the chapter prior to attending lectures on it. In this way you provide a skeleton on which to hang flesh. Prior study of the chapter makes it easier to concentrate on the lecture, to follow the ideas, and to record notes more concisely and completely. Shortly after the lecture, review your lecture notes with an eye toward improving them. Particularly, transfer facts and statements from your textbook to your lecture notebook to give more substance to your notes. Rewrite descriptions and explanations in order to make them more complete and accurate, using clear, concise language. Give informative titles to sections of your notes. State the significance of what is recorded in your notes and state generalizations, wherever these are lacking. Do what is necessary to make your notes more legible, more accurate, more complete, more informative. The very act of improving your lecture notes, as described here, is a good way to go about learning chemistry. Your lecture notes, now modified and fortified, are like a second textbook. Lecture notes and textbook alike are sacred, to be studied and restudied, again and again. If your instructor approves, you may record lectures on cassette tapes, in addition to taking lecture notes. The taped lectures can be used for modifying your written notes and as a resource for study and review. Correlate material for better understanding and retention. Correlate related items. Facts, concepts, and generalizations are more readily understood and more readily retained when they are related to each other, forming a unified picture with a central thesis. A skilled lecturer will correlate related items in this way from time to time; be alert to this during lectures. During periods of self-study correlate material whenever possible. Admittedly, this is not an easy task for a novice chemistry student to do on his own, but try anyway. A few suggestions in this respect may help you : – – – – –

Read the preface of your textbook. The preface usually gives reasons for the choice and order of chapters and topics appearing in the book. These reasons may help you correlate part of the book's contents. Frequent use of the index is helpful. Use the index to find all possible information on a given topic in your textbook. Here and there a textbook may give cross references. Follow up on these; study and tie together the cross-referenced material. Study opening paragraphs of a chapter. These transitional paragraphs invariably correlate earlier work with new work to be studied. Study chapter-end summaries. A nicely written summary will paint a unified picture of the chapter's contents.

A special and more restricted way to correlate material is described next.

Page 7 Distinguish between related items to increase your mental acuity. As your knowledge of chemistry increases, distinguish between related items. The practice of distinguishing between related items increases your mental acuity. Consider an example of a distinguishing question with answers : Question : Distinguish between an electron and a proton. Possible answers : (a) An electron has a negative one electrical charge whereas a proton has a positive one electrical charge. (b) The mass of a proton is much greater than that of an electron; the mass of an electron is about 1/1837 of that of a proton. (c) Protons are located in the nucleus of the atom whereas electrons are located outside the nucleus (extranuclear electrons). Any one of the three possible answers is a good answer; all three possible answers together is a better answer. As you acquire more and more knowledge, practice distinguishing between related items. Learn basic mathematics and solve many problems of all types. Be honest with yourself. If you are rusty in basic mathematics, then study basic mathematics prior to and during the course. Review and practice addition, subtraction, multiplication, division, fractions, percent, exponential numbers, simple algebra, and logarithms. General chemistry textbooks usually contain an appendix that covers basic mathematics needed in the course. Study that appendix and study other books found in libraries and bookstores. An electronic calculator saves time for computations. Learn to use your calculator with proficiency; this requires practice. Read the booklet that came with your calculator. Practice solving many problems of all types. Your proficiency in solving problems increases with practice. Numerical and non-numerical exercises with solutions given within the body of the chapter should be studied.. These exercises illustrate chemical concepts and often allude to practical applications. Cover up the solution and try to work out the solution by yourself. Do all of the assigned end-of-chapter exercises. If time allows, do additional companion exercises. Make problem solving a part of every study session. If you cannot work out the solution to an exercise (numerical or non-numerical type), study again the cognate topics in the textbook and in your lecture notes. Then make a second attempt to answer the problem. Only then should you consult your study guide for the solution to the exercise. Do numerical problems systematically and neatly. Give all setups and all steps. Give units and labels for all numbers at each stage of the solution. If more than one approach can be used to solve a problem, then solve it using the different approaches. After working out solutions to a set of problems, check your work against that given in the study guide. Use the factor-label method (also called dimensional analysis) wherever possible. For example, use this method to convert 2.0 hours to seconds (1 hr = 60 min and 1 min = 60 sec) : 2.0 hr ×

60 min 60 sec × = 7200 sec = 7.2 × 10 3 sec hr min

Advantages of the factor-label method are : units and labels help you set up the problem; all units should cancel out except those that should appear in the answer; when several factors are involved in the solution, the problem can be written in a single line; it is an efficient method since separate steps are avoided. If unwanted units do not cancel out, then you know that an error was made; find the error and correct the setup. One way to begin a numerical problem, particularly a complicated one, is to record on your paper, in grocery list style, the given data with units and labels, as you read the problem; also make a suitable notation of what is to be found, with units. If a reaction is involved, copy the reaction on your paper. In this way, everything you need is set down on paper in front of you; you do not have to go back again to the printed problem. The act of writing out the data and reaction will help you start thinking about how to solve the problem. Think. Try to get a clear picture of the physical setup involved in the problem. Ask yourself questions. What substances are present ? How are the substances reacting or behaving ? What chemical principles are applicable to the solution of the problem ? Frequently refresh your knowledge of chemical principles. These principles form the basis for understanding the methods used for solving numerical problems. Even though you lack clear understanding of a particular type of numerical problem, go through the mechanics of writing out detailed solutions to a number of problems of that type. There tends to be something magical about this approach; somewhere along the line you will see the light of day. In your write-up of a solution to a problem, give explanatory statements that indicate your understanding of the problem. After solving a problem, estimate whether or not the magnitude of your answer is reasonable; if it is not, find the error and correct the solution. Use the periodi c table for learning physical and chemical properties of the elements. Make the periodic table your friend. Every chemistry textbook has a table printed on the inside front cover or back cover as well as within the textbook. Every chemistry lecture room has one hanging on the wall. The periodic table is a systematic arrangement of the elements. It is a summary of data. It is useful for correlating and understanding chemical and physical properties of the elements. It is useful because you can derive information from it as you study. The periodic table will become more and more useful to you as you continue your study of chemistry.

Page 8 Learn general reactions and illustrate each general reaction with specific examples. When studying chemical properties (chemical reactions) of substances, note whether or not the chemical reaction is a general one. Knowledge of general reactions makes it easier to learn chemical properties and to predict the products of a reaction from the given reactant(s). This is true for studying inorganic and organic reactions. For inorganic reactions, keep in mind that elements in the same group of the periodic table are known to have the same or similar chemical properties. Knowing how one element in the group reacts enables you to predict how another element in the same group will react. For example, both sodium (Na) and potassium (K) are in Group IA of the periodic table. If sodium (Na) reacts with chlorine (Cl 2) to produce sodium chloride (NaCl), then, by analogy, we would expect that potassium (K) would react with chlorine (Cl 2) to produce potassium chloride (KCl) : 2 K + Cl 2 → 2 KCl This reaction does indeed occur. In fact, any Group IA alkali metal (Li, Na, K, Rb, and Cs) reacts with any Group VIIA halogen (the nonmetals F2, Cl 2, Br 2, and I2) to form an ionic compound (a salt) consisting of alkali metal cations with a +1 charge and halide anions with a -1 charge. The general equation for this type of reaction is : 2 M + X2 → 2 MX where, M = alkali metal (e.g., Na) X2 = halogen (e.g., Cl 2) MX = salt (e.g., NaCl) These reactions, together with other reactions, also allow us to write a more general reaction : metal + non-metal → ionic compound Learn general reactions. Practice writing specific reactions that illustrate each general reaction. Where appropriate, write the general reaction that corresponds to the specific reaction(s) studied. Chemical reactions also are classified more broadly as combination (synthesis), decomposition, oxidation-reduction, single displacement, and metathesis (double displacement). Many reactions fit into more than one class. For example, the reaction of an alkali metal with a halogen to give a salt, as described above, is both a combination (synthesis) reaction and an oxidationreduction reaction (involves electron transfer). Learn to recognize these broad classes of reactions. Know the significance of all reactions studied. Organic chemistry : memorize types of organic compounds and types of organic reactions. Suggestions for the study of chemistry given so far in this book also apply to the study of the organic chemistry portion and the biochemistry portion of the general chemistry course. A few of these suggestions will be repeated here; several new ones will be added. Repetitive study is necessary for learning organic chemistry. Go over the material again and again. Use pen and paper as you study. Practice writing structural formulas of organic compounds and chemical reactions at every opportunity. The large number of known organic compounds are classified according to types. Each type of organic compound is distinguished by its functional group (center of reactivity). At the beginning of your study of organic chemistry, learn to write the general structure of each type of organic compound. Practice writing structural formulas of specific compounds that illustrate each type. Be able to recognize the type of compound from inspection of the structural formula of a specific example. Knowledge of types of organic compounds serves as a framework for your study of organic chemistry. Initially, practice writing structural formulas of organic compounds in the expanded form; thereafter, write them in the condensed form. The condensed form is easier on the eyes and faster to write. Consider an example. Alkenes are one type of organic compound. The general formula of alkenes may be represented by RCH=CH2. The C=C (carbon-carbon double bond) is the functional group of alkenes. Expanded and condensed structural formulas of a specific alkene are shown below. The formal name of this alkene is ethene; the common name, ethylene. H

H C

H

CH2 CH2

C H

Organic molecules are three-dimensional. Make molecular models of organic molecules to help you visualize the spatial relationships of the atoms and groups of atoms in the molecule. Inexpensive modal kits may be purchased from the chemistry storeroom or from the student bookstore. Memorize general types of reactions. Types of reactions are reactions of functional groups. A general reaction is one for which a large number of specific examples are known. Practice writing the general equation for each type of reaction. Note the net change in structure that occurs in going from reactant to product. Using structural formulas, practice writing specific reactions that illustrate each general type of reaction. Reactions also are classified more broadly as addition, elimination, substitution, condensation, and so on. Learn to recognize these classes of reactions. Consider an example. Catalytic hydrogenation (reduction) of a ketone gives a secondary alcohol.

Page 9 H2, Ni

R C R O ketone

R CH R OH secondary alcohol

This reaction is a general reaction. The reaction involves addition of H2 to the carbonyl group (>C=O) of the ketone to give a hydroxyl group (>CH–OH). A specific example is shown below. CH3

C

CH3

O propanone (acetone)

H2, Ni

CH3

CH CH3

OH 2-propanol (isopropyl alcohol)

As an aid in learning organic reactions, make a scheme of related general reactions whenever possible. An example is shown as follows. This scheme summarizes some of the addition reactions of alkenes (addition of reagents to the carbon-carbon double bond, >C=C<) and some of the elimination reactions that give an alkene as product. In general, schemes of this sort give you a bird's eye view of related organic reactions. Making the scheme itself forces you to correlate and unify related reactions. During your study of organic chemistry, make schemes of this sort, whenever possible, as an aid in learning organic reactions. R CH2

CH R

X haloalkane (alkyl halide) ethanolic KOH, heat dehydrohalogenation (-HX) R CH CH R X

X

vicinal dihalide

HX hydrohalogenation

X2 halogenation Zn dehalogenation (-X2)

H2 , Ni R CH CH R alkene (olefin)

acid, heat dehydration

R CH2

R CH2 CH2 R catalytic hydrogenation (reduction)

alkane (paraffin)

+

H 2O, H hydration

CH R OH

alcohol

Using pen and paper, answer all assigned problems. When doing problems, take the opportunity to do more than give the desired answer to the problem. Note the functional group or groups present in the molecule. Classify each compound according to type. Give the formal and common names of the compound. If a reaction is involved, note the net change in structure that occurs in going from reactant to product. Write the general reaction that corresponds to the specific reaction studied. Classify the reaction as addition, elimination, substitution, condensation, and so on. These practices help you distinguish the forest from the trees. If you cannot answer a problem, study again the cognate material in your textbook and lecture notes; then make a second attempt to answer the problem. Check your answers against those given in the study guide. The study guide may give alternate ways to answer a problem.

Page 10 Study biochemistry like organic chemistry and learn metabolic pathways. The study of biochemistry is an extension of the study of organic chemistry. The biomolecules are organic compounds; the metabolic pathways involve reactions of organic compounds. Learn the structures of the biomolecules, the typical enzymatic and non-enzymatic reactions the biomolecules undergo, the steps in the main metabolic pathways, and the significance of each pathway in the life of the organism. Most of the chemical reactions the biomolecules undergo are of the same type as regular organic reactions. For example, dehydration of a tertiary alcohol to give an alkene is a general reaction. Loss of H2O from the tertiary alcohol generates a new carbon-carbon double bond, >C=C< : R conc. H2SO4, heat (loss of H2O)

R C CH2 R OH tertiary alcohol

R R C CH R alkene

The same type of chemical reaction - dehydration of a tertiary alcohol-occurs in the biochemical transformation of citrate to cis-aconitate in the Krebs cycle : -

CH2 COO HO C COO

-

CH2 COO citrate

enzyme (loss of H2 O)

CH2 COO

-

-

C COO

CH COO

-

cis-aconitate

Here, too, loss of H2O from the tertiary alcoholic group of citrate gives a new carbon-carbon double bond. Study the reactions of the biomolecules in the same way you study regular organic reactions. Study for tests well in advance. Begin preparation for a test many days in advance. Avoid cramming; there is too much to review. Here is one prescription for preparing for a test : – – – – – – – –

Use a pen and paper as you study. First study your lecture notes. Rework problems given in your lecture notes; cover up the solution and see if you can answer the problem. Then read sections in your textbook that are companions to the topics in your lecture notes. Correlate textbook material with lecture notes. Rework assigned chapter-end problems and rework problems given within the body of the chapter. If old tests are available, write out answers to the questions. Compose your own questions; then answer them.

Try to study when sickness strikes. If sickness strikes, causing you to miss classes, a classmate could make photocopies of lecture notes and record lectures on tape. While confined to bed or home, you could try to keep up with the course by studying the lecture notes and textbook and listening to the tapes.

The purpose of this little book is to provide realistic suggestions for the study of chemistry. My hope is that you will put these suggestions into practice and that you will be successful in your study of chemistry. The study of chemistry takes time, but, then, anything worthwhile takes time. The study of chemistry is hard work; and I never said it was anything else. Your comments and suggestions for improving this little book are welcome.