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BIG Idea

Most compounds containing the element carbon are organic compounds.

24. 1 Simple Organic Compounds

MAIN Idea Hydrocarbons are compounds made only of carbon and hydrogen atoms.

24.2 Other Organic Compounds

MAIN Idea Substituted hydrocarbons contain other elements besides carbon and hydrogen.

24.3 Petroleum--A Source of Carbon Compounds

MAIN Idea Petroleum is the source of carbon compounds used to make plastics, fossil fuels, and many other products.

24.4 Biological Compounds

MAIN Idea Proteins, nucleic acids, carbohydrates, and lipids are polymers made by plants and animals.

What's in the willows?

The bark of willow trees has been used to treat pain and fever. Willow bark contains a compound related to aspirin. Today, aspirin and thousands of other useful substances are synthesized from compounds found in petroleum.

Science Journal

List other medicines from natural sources, such as plants.

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Walter Bibikow/Index Stock Imagery

Start-Up Activities

Carbon, the Organic Element

The element carbon exists in three very different forms: dull, black charcoal; slippery, gray graphite; and bright, sparkling diamond. However, this is nothing compared with the millions of different compounds that carbon can form. In this lab, you will seek out the carbon hidden in two common substances.

WARNING: Always use extreme caution around an open flame. Point test tubes away from yourself and others.

Organic Compounds Make the following Foldable to help you understand the vocabulary terms in this chapter.

STEP 1 Fold a vertical sheet of notebook paper from side to side.

STEP 2 Cut along every third line of only the top layer to form tabs.

1. Place a small piece of bread in a test tube.

2. Using a test-tube holder, hold the tube over the flame of a laboratory burner until you observe changes in the bread.

3. Using a clean test tube and a small amount of paper instead of bread, repeat step 2.

4. Think Critically Based on what you observed and what remained in the test tubes, infer what these residues might be.

Build Vocabulary As you read the chapter, list the vocabulary words about organic compounds on the tabs. As you learn the definitions, write them under the tab for each vocabulary word.

Preview this chapter's content and activities at

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Walter Bibikow/Index Stock Imagery

Simple Organic Compounds

Reading Guide

Identify the difference between organic and inorganic carbon compounds.

Examine the structures of some organic compounds.

Differentiate between saturated and unsaturated hydrocarbons.

Identify isomers of organic compounds.

Carbon compounds surround you-- they're in your food, your body, and most materials you use every day.

Review Vocabulary

compound: substance formed from two or more elements

New Vocabulary

organic compound

? hydrocarbon ? saturated hydrocarbon ? isomer ?? unsaturated hydrocarbon

Organic Compounds

What do you have in common with your athletic shoes, sunglasses, and backpack? All the items shown in Figure 1 contain compounds of the element carbon--and so do you. Most compounds containing the element carbon are organic compounds.

At one time, scientists thought that only living organisms could make organic compounds, which is how they got their name. By 1830, scientists could make organic compounds in laboratories, but they continued to call them organic.

Of the millions of carbon compounds known today, more than 90 percent of them are considered organic. The others, including carbon dioxide and the carbonates, are considered inorganic.

Figure 1 Most items used every

day contain carbon.

Bonding You may wonder why carbon can form so many organic

compounds. The main reason is that a carbon atom has four electrons in its outer energy level. This means that each carbon atom can form four covalent bonds with atoms of carbon or with other elements. As you have learned, a covalent bond is formed when two atoms share a pair of electrons. This large number of bonds allows carbon to form many types of compounds ranging from small compounds used as fuel, to complex compounds found in medicines and dyes, and the polymers used in plastics and textile fibers.

726 CHAPTER 24 Organic Compounds

KS Studios

Arrangement Another reason carbon can form so many

compounds is that carbon can link together with other carbon atoms in many different arrangements--chains, branched chains, and even rings. It also can form double and triple bonds as well as single bonds. In addition, carbon can bond with atoms of many other elements, such as hydrogen and oxygen. Figure 2 shows some possible arrangements for carbon compounds.

Hydrocarbons

Carbon forms an enormous number of compounds with hydrogen alone. A compound made up of only carbon and hydrogen atoms is called a hydrocarbon. Does the furnace, stove, or water heater in your home burn natural gas? A main component of the natural gas used for these purposes is the hydrocarbon methane. The chemical formula of methane is CH4.

Methane can be represented in two other ways, as shown in Figure 3. The structural formula uses lines to show that four hydrogen atoms are bonded to one carbon atom in a methane molecule. Each line between atoms represents a single covalent bond. The second way, the space-filling model, shows a more realistic picture of the relative size and arrangement of the atoms in the molecule. Most often, however, chemists use chemical and structural formulas to write about reactions.

Name three ways that chemists represent organic compounds.

Another hydrocarbon used as fuel is propane. Some stoves, most outdoor grills, and the heaters in hot-air balloons burn this hydrocarbon, which is found in bottled gas. Propane's structural formula and space-filling model also are shown in Figure 3.

Methane and other hydrocarbons produce more than 90 percent of the energy humans use. Carbon compounds also are important in medicines, foods, and clothing. To understand how carbon can play so many roles, you must understand how it forms bonds.

Figure 2 Carbon atoms bond to

form straight, branched, and cyclic chains.

HHHHHHH H -- C -- C -- C -- C -- C -- C -- C -- H

HHHHHHH Heptane is found in gasoline.

---- ---- ---- ---- ---- ---- ----

H

-- --

H -- C -- H

H

H

C--C--C--C

H

HH

Isoprene exists in natural rubber.

OH

H

-- ----

-- --

--

H C --C C O -- C -- H H

H C C --C H

H C-- O Vanillin is found in vanilla flavoring.

Figure 3 Natural gas is mostly

methane, CH4, but bottled gas is mostly propane, C3H8. Compare and contrast the two

gases.

HH HH----CC----HH

HH

Methane CH4

---- ---- ---- ---- ----

HHH H -- C -- C -- C -- H

HHH

Propane C3H8

SECTION 1 Simple Organic Compounds 727

Table 1 Some Hydrocarbons

Single Bonds

In some hydrocarbons, the carbon atoms are

Na

tructural Formula

joined by single covalent bonds. Hydrocarbons containing only single-bonded carbon atoms are

H

called saturated hydrocarbons. Saturated means

Me

| H--C--H

|

that a compound holds as many hydrogen atoms as possible--it is saturated with hydrogen atoms.

H

H H

What are saturated

| |

Eth

H--C-- C--H

hydrocarbons?

| | H H

Table 1 lists four saturated hydrocarbons.

H H H

Notice how each carbon atom appears to be a

Pro

| | | H--C-- C-- C--H

link in a chain connected by single covalent

| | |

bonds. Figure 4 shows a graph of the boiling

H H H

points of some hydrocarbons. Notice the rela-

H H H H | | | |

tionship between boiling points and the addi-

Bu

H--C-- C-- C-- C--H | | | |

tion of carbon atoms.

H H H H

Structural Isomers Perhaps you have seen

or know about butane, which is a gas that some-

times is burned in camping stoves and lighters. The chemical

formula of butane is C4H10. Another hydrocarbon called isobutane has exactly the same chemical formula. How can this be?

The answer lies in the arrangement of the four carbon atoms.

Look at Figure 5. In a molecule of butane, the carbon atoms

form a continuous chain. The carbon chain of isobutane is

branched. The arrangement of carbon atoms in each compound

changes the shape of the molecule, and very often affects its

physical properties, as you will soon see. Isobutane and butane

are isomers.

Figure 4 Boiling points of

hydrocarbons increase as the number of carbon atoms in the chain increases. Predict the approximate boiling point of hexane.

Boiling point (C)

50 0 ?50

?100 ?150 ?200

0

Boiling Points of Hydrocarbons

Propane Ethane

Pentane Butane

Methane

1

2

3

4

5

6

Number of carbon atoms in chain

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