Modeling Organic Chemistry

Transcription

1 Modeling Organic Chemistry Topic The shapes of hydrocarbon chains can be analyzed with models. Introduction With a few exceptions, including carbon dioxide and carbon monoxide, organic compounds are those that contain carbon. Carbon has four electrons in its outer valence shell, but it is more stable when its outer shell has a complete set of eight electrons. To fill the outer electron shell, carbon tends to form covalent bonds with other molecules. For this reason, carbon usually exists in compounds in which it can create four covalent bonds. Many carbon compounds are long chains or ring structures in which the carbon atoms bond to each other or to hydrogen (see Figure 1). Carbon atoms are also capable of bonding to an array of different functional groups such as amines (NH3) and hydroxides (OH). hydrogen carbon covalent bonds Figure 1 The simplest of all organic molecules, the hydrocarbons, are composed of chains of carbon atoms bonded to hydrogen atoms. These may be indefinitely long and can be combined with functional groups such as hydroxides or amines. Hydrocarbon chains can be classified as saturated or unsaturated. Saturated hydrocarbons contain only single bonds between carbon atoms and are considered to be saturated with

2 MODELING ORGANIC CHEMISTRY 2 hydrogen. Unsaturated hydrocarbons contain double or triple bonds between carbon atoms. When adjacent carbon atoms form two or more bonds between them, they cannot bond with as many hydrogen atoms. In this experiment, you will create models of various organic compounds and relate their molecular structure to their behavior. Time Required 30 minutes Materials toothpicks gumdrops (2 different colors) access to the Internet, a chemistry textbook, or chemical handbooks science notebook Safety Note Wear safety goggles and tie back long hair. Please review and follow the safety guidelines. Procedure 1. Use two colors of gumdrops to represent carbon and hydrogen atoms. Designate one color for each type. 2. On the Internet, or in your chemistry textbook or chemical handbooks, research the structure and characteristics of methane, CH4. Use your findings to construct a model of CH4. Connect gumdrops with toothpicks to form the model. Each toothpick will represent one bond. (HINT: Remember that carbon atoms always form four bonds). 3. In the third column of the data table, sketch your model. In the last column of the data table, describe some of the characteristics of this molecule that you learned during your research.

3 MODELING ORGANIC CHEMISTRY 3 4. Repeat steps 2 and 3 for the other hydrocarbons in the data table. Data Table 1 Name of Molecular formula Sketch of model Characteristics hydrocarbon of hydrocarbon methane CH4 butane C4H12 butene C4H8 butyne C4H6 hexane C6H14 hexene C6H12 octane C8H18 octene C8H16

4 MODELING ORGANIC CHEMISTRY 4 Analysis 1. How are the structures of saturated and unsaturated hydrocarbons different? 2. What does the prefix but- mean? 3. How is a compound with a name that ends in -ane different from one with a name that ends in -ene? 4. In hydrocarbons, what are the two atoms with which carbon atoms form bonds? 5. The chains of unsaturated carbon atoms are more flexible than those that are saturated. Which type of hydrocarbon would more likely be solid at room temperature? Why? What s Going On? Hydrocarbons can be saturated or unsaturated. Those that are saturated are known as alkanes. Alkanes have only single bonds and their names end in the suffix -ane. Unsaturated hydrocarbons may be either alkenes or alkynes. Alkenes have at least one double bond; their names end in -ene. Alkynes have triple bonds, and their names end in -yne. The presence of double or triple bonds between carbons changes the shape of a hydrocarbon. Saturated hydrocarbons tend to form relatively straight lines, whereas unsaturated hydrocarbons have more bends in their structure. Long saturated hydrocarbons are more likely to form solids at room temperature than unsaturated ones since their structure enables them to be packed more closely together. The location of double or triple bonds within an unsaturated hydrocarbon is important in establishing the structure of that molecule. When carbon molecules bond more than once with each other, their configuration is more solid than when they are single bonded, and the structure is less likely to move or rotate. Often, double and triple bonds will form isomers, structures that are locked in to a particular configuration. If functional groups are locked into positions at opposite ends of a hydrocarbon, they will cause two molecules with the same molecular formula to behave in very distinct ways chemically. Want to Know More? See Our Findings.

5 OUR FINDINGS 2.7 MODELING ORGANIC CHEMISTRY Suggestion for class discussion: Ask students to give some examples of models used in science. Many may be familiar with models of the solar system. Explain that atoms and molecules are too small to be seen, but understanding their three-dimensional structure is useful in the study of chemistry. Point out that models make abstract concepts easier to understand. Analysis 1. Saturated hydrocarbons have single bonds and unsaturated hydrocarbons have multiple bonds. (As a result, hydrocarbon chains with unsaturated bonds are more flexible and not as straight as those that are saturated.) 2. containing a group of four 3. Compounds with names that end in -ane are saturated and those with names that end in -ene are unsaturated. 4. hydrogen and carbon 4. Saturated hydrocarbons are more likely to be solid at room temperature because they are straighter and will pack closer together than unsaturated ones.

6 SAFETY PRECAUTIONS Review Before Starting Any Experiment Each experiment includes special safety precautions that are relevant to that particular project. These do not include all the basic safety precautions that are necessary whenever you are working on a scientific experiment. For this reason, it is absolutely necessary that you read and remain mindful of the General Safety Precautions that follow this note. Experimental science can be dangerous, and good laboratory procedure always includes following basic safety rules. Things can happen very quickly while you are performing an experiment. Materials can spill, break, or even catch fire. There will be no time after the fact to protect yourself. Always prepare for unexpected dangers by following the basic safety guidelines during the entire experiment, whether or not something seems dangerous to you at a given moment. We have been quite sparing in prescribing safety precautions for the individual experiments. For one reason, we want you to take very seriously every safety precaution that is printed in this book. If you see it written here, you can be sure that it is here because it is absolutely critical. Read the safety precautions here and at the beginning of each experiment before performing each lab activity. It is difficult to remember a long set of general rules. By rereading these general precautions every time you set up an experiment, you will be reminding yourself that lab safety is critically important. In addition, use your good judgment and pay close attention when performing potentially dangerous procedures. Just because the book does not say Be careful with hot liquids or Don t cut yourself with a knife does not mean that you can be careless when boiling water or using knives. Notes in the text are special precautions to which you must pay special attention. GENERAL SAFETY PRECAUTIONS Accidents caused by carelessness, haste, insufficient knowledge, or taking an unnecessary risk can be avoided by practicing safety procedures and being alert while conducting experiments. Be sure to check the individual experiments in this book for additional safety regulations and adult supervision requirements. Anytime you are working with an electrical current, it becomes possible to shock yourself on exposed wires. If you will be working in a lab, do not work alone. When

7 SAFETY PRECAUTIONS 2 you are working off-site, keep in groups with a minimum of three students per group, and follow school rules and state legal requirements for the number of supervisors required. Ask an adult supervisor with basic training in first aid to carry a small first-aid kit. Make sure everyone knows where this person will be during the experiment. PREPARING Clear all surfaces before beginning experiments. Read the instructions before you start. Know the hazards of the experiments and anticipate dangers. PROTECTING YOURSELF Follow the directions step by step. Do only one experiment at a time. Locate exits, fire blanket and extinguisher, master gas and electricity shut-offs, eyewash, and first-aid kit. Make sure there is adequate ventilation. Do not horseplay. Keep floor and workspace neat, clean, and dry. Clean up spills immediately. If glassware breaks, do not clean it up by yourself; ask for teacher assistance. Tie back long hair. Never eat, drink, or smoke in the laboratory or workspace. Do not eat or drink any substances tested unless expressly permitted to do so by a knowledgeable adult. USING EQUIPMENT WITH CARE Set up apparatus far from the edge of the desk. Use knives or other sharp, pointed instruments with care. Pull plugs, not cards, when removing electrical plugs. Clean glassware before and after use. Check glassware for scratches, cracks, and sharp edges. Let your teacher know about broken glassware immediately. Do no use reflected sunlight to illuminate your microscope. Do not touch metal conductors. Use alcohol-filled thermometers, not mercury-filled thermometers.

8 SAFETY PRECAUTIONS 3 USING CHEMICALS Never taste or inhale chemicals Label all bottles and apparatus containing chemicals Read labels carefully. Avoid chemical contact with skin and eyes (wear safety glasses, lab apron, and gloves). Do not touch chemical solutions. Wash hands before and after using solutions. Wipe up spills thoroughly. HEATING SUBSTANCES Wear safety glasses, apron, and gloves when boiling water. Keep your face away from test tubes and beakers. Use test tubes, beakers, and other glassware made of Pyrex glass. Never leave apparatus unattended. Use safety tongs and heat-resistant gloves. If your laboratory does not have heat-proof workbenches, put your Bunsen burner on a heat-proof mat before lighting it. Take care when lighting your Bunsen burner; light it with the airhole closed, and use a Bunsen burner lighter rather than wooden matches. Turn off hot plates, Bunsen burners, and gas when you are done. Keep flammable substances away from flames and other sources of heat. Have a fire extinguisher on hand. FINISHING UP Thoroughly clean your work area and any glassware used. Wash your hands. Be careful not to return chemicals or contaminated reagents to the wrong containers. Do not dispose of materials in the sink unless instructed to do so. Clean up all residues and put in proper containers for disposal. Dispose of all chemicals according to all local, state, and federal laws. BE SAFETY CONSCIOUS AT ALL TIMES!