Carbon Chemistry. Elemental Carbon and Simple Organic Compounds

Transcription

1 CAPTER 14 Carbon Chemistry LESSON 1 Elemental Carbon and Simple Organic Compounds What do you think? Read the two statements below and decide whether you agree or disagree with them. Place an A in the Before column if you agree with the statement or a D if you disagree. After you ve read this lesson, reread the statements to see if you have changed your mind. Before Statement After Key Concepts ow is carbon unique compared to other elements? ow does carbon bond with other carbon atoms? 1. Charcoal and diamonds are made of carbon atoms. 2. Carbon atoms often bond with hydrogen atoms in chemical compounds. Elements in Living Things All living organisms, such as humans, starfish, sunflowers, and mosquitoes, have several things in common. They are made of cells that contain carbon, hydrogen, oxygen, nitrogen, and other elements. About 18 percent of the mass of all living organisms is made of compounds that contain the element carbon. Except for water and some salts, most things that you put in or on your body consist of compounds that contain carbon. These carbon compounds could be food, clothing, cosmetics, or medicine. Organic Compounds In the past, scientists thought that all carbon compounds came from organisms that were alive or were once alive. They called carbon compounds organic compounds because of this connection with organisms. Scientists now know that carbon is also in many nonliving things. Today, scientists define an organic compound as a chemical compound that contains carbon atoms usually bonded to at least one hydrogen atom. Compounds such as carbon dioxide (CO 2 ) and carbon monoxide (CO) are not organic because they do not have a carbon-hydrogen bond. Build Vocabulary Skim the headings in this lesson and circle any words that you do not know. After you read the lesson, go back and define these words. Refer to these definitions as you study the lesson. Reading Check 1. Identify Which four elements are in most living organisms? Reading Essentials Carbon Chemistry 247

2 REVIEW VOCABULARY covalent bond a chemical bond formed by the sharing of one or more pairs of electrons between atoms Visual Check 2. Identify For each carbon-hydrogen bond, how many electrons c ome from a hydrogen atom? Understanding Carbon A carbon atom is a unique element. It can easily combine with other atoms and form millions of compounds. Carbon has the atomic number 6. This means that a neutral carbon atom has six protons and six electrons. Four of these electrons are valence electrons which are in the outermost energy level. Atoms are chemically stable when they have eight valence electrons. Carbon atoms become more chemically stable through covalent bonding, as shown below. In a covalent bond, carbon atoms have eight valence electrons, like a stable, unreactive noble gas. Carbon often bonds with four hydrogen atoms. For each carbon-hydrogen covalent bond, the hydrogen atom donates one electron and the carbon atom donates one electron, creating a shared pair. 2 electrons 4 electrons + 1 electron C 4 C Key Concept Check 3. Describe ow is carbon unique compared to other elements? The Carbon Group The periodic table shows you that silicon and germanium are in the same group as carbon. This means that their atoms also have four valence electrons. Atoms of silicon and germanium become stable by forming four covalent bonds. owever, it takes more energy for them to do this. The more energy it takes, the less likely it is that bonding will occur. The Forms of Pure Carbon When carbon atoms bond together, they form one of several different arrangements. Forms of pure carbon are discussed below and shown in the figure on the next page. Graphite In graphite (GRA fite), carbon atoms form thin sheets. The thin sheets are held together by weak forces. These thin sheets can slide over one another or bend. Graphite is used as a lubricant (LEW brih kunt), a frictionreducing film. It is also used in making golf clubs, tennis rackets, pencil lead, and other items. 248 Carbon Chemistry Reading Essentials

3 Diamonds Not only are diamonds used in jewelry, but also on the tips of drill bits and the cutting edges of some saw blades. Each carbon atom in a diamond is tightly bonded to four other carbon atoms. The bonds between carbon atoms in diamonds are extremely strong. These strong bonds make diamonds one of the hardest materials known. Fullerene Carbon atoms in fullerene (FOOL uh reen) are cagelike structures, as shown below. Fullerene was discovered late in the twentieth century, and uses for it are still being explored. owever, future fullerene uses might include the development of faster, smaller electronic components. Amorphous The atoms in amorphous (uh MOR fus) carbon lack an orderly arrangement. Amorphous carbon is found in soot, coal, and charcoal. Each form of carbon is shown below. Forms of Carbon Graphite Diamond Visual Check 4. Compare the structures of graphite and diamonds. Why is graphite used in pencil lead but diamonds are not? Fullerene Buckyball Nanotube Amorphous Carbon ydrocarbons Many organic compounds contain only carbon and hydrogen atoms. A compound that contains only carbon and hydrogen atoms is called a hydrocarbon. There are many different hydrocarbons. The simplest is methane (C 4 ). Reading Essentials Carbon Chemistry 249

4 Reading Check 5. Name What kind of chains do carbon atoms form? ydrocarbon Chains When carbon atoms form hydrocarbons, the carbon atoms can link together in different ways. They can form straight chains, branched chains, or rings. Look closely at the molecular formula for each of the compounds in the table below. Notice that butane and isobutane have the same molecular formula. They have the same ratio of carbon atoms to hydrogen atoms. Compounds that have the same molecular formula but different structural arrangements are called isomers (I suh murz). Each isomer is a different molecule with its own unique name and properties. Butane Isobutane Cyclobutane Molecular formula: C 4 10 Molecular formula: C 4 10 Molecular formula: C 4 8 Interpreting Tables 6. Compare butane and isobutane. C C C C Structural formula C C C C Structural formula C C C C Structural formula Key Concept Check 7. Describe What kind of bonds do carbon atoms form with other carbon atoms? Carbon-to-Carbon Bonding When a carbon atom bonds to another carbon atom, the two atoms can share two, four, or six electrons. These different options are shown in the figure on the next page. The result of each of these cases is that the carbon atoms in each molecule have eight valence electrons and are stable. When two carbon atoms share two electrons, they form a single bond. A hydrocarbon that has only single bonds is called an alkane. When two carbon atoms share four electrons, they form a double bond. A hydrocarbon that has at least one double bond is called an alkene. When two carbon atoms share six electrons, they form a triple bond. A hydrocarbon that has at least one triple bond is called an alkyne. 250 Carbon Chemistry Reading Essentials

5 Alkane single bond two electrons shared between two carbon atoms C 3 C 3 single line denotes single bond double line denotes double bond Alkene double bond four electrons shared between two carbon atoms C 2 C 2 Make a three-quarter book to organize your notes about hydrocarbons and how they bond. ydrocarbons 1. What is a hydrocarbon? 2. What is an alkane? 3. What is an alkene? C C C C 4. What is an alkyne? triple line denotes triple bond Alkyne triple bond six electrons shared between two carbon atoms C C C C Visual Check 8. Identify What type of bond is found in alkene? Saturated ydrocarbons ydrocarbons are often classified by the type of bonds the carbon atoms share. A hydrocarbon that contains only single bonds is called a saturated hydrocarbon. It is called saturated because no more hydrogen atoms can be added to the molecule. An alkane, shown above, is a saturated hydrocarbon. Three of the valance electrons in each carbon atom bond with hydrogen atoms. The carbon atoms are saturated with hydrogen atoms. Unsaturated ydrocarbons A hydrocarbon that contains one or more double or triple bonds is called an unsaturated hydrocarbon. An alkene has a double bond. An alkyne has a triple bond. If the double and triple bonds are broken, additional hydrogen atoms could bond to the carbon atoms. This means that double and triple bonds are not saturated with hydrogen atoms. These molecules, shown above, are unsaturated. Naming ydrocarbons Most geometric shapes have names that refer to the number of sides they have. For example, a triangle has three sides, and the prefix tri means three. ydrocarbons have names that indicate how many carbon atoms are in each molecule. Reading Check 9. Compare What is the difference between saturated and unsaturated hydrocarbons? Reading Essentials Carbon Chemistry 251

6 Carbon Chains When naming a hydrocarbon, the first thing you need to do is find the longest carbon chain and count the number of carbon atoms in it. Look at the figure below. The carbon chain is formed by the darker atoms. Find the carbon chain and count the carbon atoms. There are four carbon atoms in this molecule. The number of carbon atoms gives you the root word of the name. Now look at the table below. This table shows the root word for any hydrocarbon that has one through ten carbon atoms. What is the root name for the molecule below? The molecule has four carbon atoms, so the root name is but (BYEWT). Visual Check 10. Analyze ow many carbon atoms are in this hydrocarbon (C 4 10 )? (Circle the correct answer.) a. 2 b. 4 c. 10 Interpreting Tables 11. Identify ow many carbon atoms are in a molecule with the root word hept? Carbon Atoms C 4 10 Name Root Words Carbon Atoms Name 1 meth 6 hex 2 eth 7 hept 3 prop 8 oct 4 but 9 non 5 pent 10 dec Determine the Suffix Now that you know how to find the root word of a hydrocarbon, you must also find the suffix, or end, of the name. Recall that carbon atoms bond to other carbon atoms with single, double, or triple bonds. The table below shows which suffix to use when you know the type of bond. Bond Type All single bonds C C Suffix ane At least one double bond C C ene At least one triple bond C C yne 252 Carbon Chemistry Reading Essentials

7 Look again at the molecule on the previous page. The molecule has only single bonds. This means that it should have the suffix ane. Thus, when you put the root and the suffix together, you get the name for the molecule. It is butane. The table below lists the steps for naming hydrocarbons. Determine the Prefix Sometimes hydrocarbons have a prefix and sometimes they do not. Recall that hydrocarbons form chains, branched chains, and rings. If a hydrocarbon contains a ring structure, the prefix cyclo is added before the root name. Reading Check 12. Name the hydrocarbon with six carbon atoms that contains only single bonds. Steps for Naming ydrocarbons 1. Examine the compound. 2. Count the number of carbon atoms in the longest continuous chain. Example A C C C C There are 4 carbon atoms in the longest chain. Example B C 2 C 2 C 2 C 2 C 2 C 2 There are 6 carbon atoms in the longest chain. 3. Determine the root name of the hydrocarbon (see the Root Words chart on page 6). 4. Determine the type of bonds in the hydrocarbon, then use the table on page 6 to find the suffix. 5. Put the root and suffix together to name the hydrocarbon. 6. If the hydrocarbon is a ring, add cyclo to the beginning of the name. The root name is but. There is a triple bond, so add the suffix yne. Combining the root and suffix gives the name butyne. No prefix is needed because the structure is not a ring. The name of the hydrocarbon is butyne. The root name is hex. There are only single bonds, so add the suffix ane. Combining the root and suffix gives the name hexane. The structure is a ring, so the prefix cyclo is added to the name. The name of the hydrocarbon is cyclohexane. Interpreting Tables 13. Explain When should cyclo be added to the beginning of the hydrocarbon name? Reading Essentials Carbon Chemistry 253

8 Mini Glossary hydrocarbon: a compound that contains only carbon and hydrogen atoms isomers (I suh murz): compounds that have the same molecular formula but different structural arrangements saturated hydrocarbon: a hydrocarbon that contains only single bonds unsaturated hydrocarbon: a hydrocarbon that contains one or more double or triple bonds organic compound: a chemical compound that contains carbon atoms usually bonded to at least one hydrogen atom 1. Review the terms and their definitions in the Mini Glossary. Write a brief explanation of how scientists definition of the term organic compound has changed over time. 2. Complete and fill in the steps below to name the following unknown hydrocarbon. C C C C a. Count the number of carbon atoms in the longest chain. b. Determine the root name. c. Determine the suffix. d. Name the hydrocarbon. 3. In what ways do you use carbon in everyday life? What do you think Reread the statements at the beginning of the lesson. Fill in the After column with an A if you agree with the statement or a D if you disagree. Did you change your mind? ConnectED Log on to ConnectED.mcgraw-hill.com and access your textbook to find this lesson s resources. END OF LESSON 254 Carbon Chemistry Reading Essentials