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Carbon Chemistry

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

1. Charcoal and diamonds are made of carbon atoms.

2. Carbon atoms often bond with hydrogen atoms in chemical compounds.

CHAPTER 14 LESSON 1

Key Concepts

? How is carbon unique compared to other elements?

? How does carbon bond with other carbon atoms?

Copyright ? Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

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 (CO2) 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

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 come from a hydrogen atom?

Key Concept Check 3. Describe How is carbon unique compared to other elements?

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

1 electron

4 electrons

+

H

C

4H

HCH

H

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. However, 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.

Copyright ? Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

248 Carbon Chemistry

Reading Essentials

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. However, 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

Fullerene Buckyball

Amorphous Carbon

Visual Check

4. Compare the structures

of graphite and diamonds. Why is graphite used in pencil lead but diamonds are not?

Nanotube

Hydrocarbons

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 (CH4).

Copyright ? Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

Reading Essentials

Carbon Chemistry 249

Reading Check 5. Name What kind of chains do carbon atoms form?

Interpreting Tables 6. Compare butane and

isobutane.

Hydrocarbon 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: C4H10

Molecular formula: C4H10

Molecular formula: C4H8

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

H

HHHH

H --C --H

H

H

H--C--C--C--C--H H--C--C--C--H

HHHH Structural formula

HHH Structural formula

HH H--C--C-- H H--C--C-- H

HH Structural formula

Copyright ? Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

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

Alkane ? single bond

? two electrons shared between two carbon atoms

CH3 -- CH3

single line denotes single bond

Alkene ? double bond

? four electrons shared between two carbon atoms

double line denotes double bond

CH2 -- CH2

HH HC C H

HH

HC C H HH

Alkyne ? triple bond

? six electrons shared between two carbon atoms

triple line denotes triple bond

CH ---- CH

HC C H

Saturated Hydrocarbons

Hydrocarbons 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 Hydrocarbons

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 Hydrocarbons

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." Hydrocarbons have names that indicate how many carbon atoms are in each molecule.

Make a three-quarter book to organize your notes about hydrocarbons and how they bond.

Hydrocarbons43. 2.WW.1hW.hhaWhaytatdhistriasaoitsacniansaanaralbkalkoylkennane?ne?e??

Visual Check 8. Identify What type of bond is found in alkene?

Reading Check 9. Compare What is the difference between saturated and unsaturated hydrocarbons?

Copyright ? Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

Reading Essentials

Carbon Chemistry 251

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