chapter 2 the chemistry of life summary -...

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© Pearson Education, Inc., publishing as Pearson Prentice Hall.59

Chapter 2 The Chemistry of Life

2–1 The Nature of MatterThe basic unit of matter is the atom. Thesubatomic particles that make up atoms areprotons, neutrons, and electrons. Protonsand neutrons have about the same mass.Protons are positively charged particles (+),and neutrons carry no charge. Protons andneutrons together form the nucleus, at thecenter of the atom. The electron is a nega-tively charged particle (–). Atoms haveequal numbers of electrons and protons,and therefore atoms do not have a charge.

A chemical element is a pure substancethat consists entirely of one type of atom.The number of protons in an atom of an ele-ment is the element’s atomic number.Atoms of an element can have differentnumbers of neutrons. Atoms of the sameelement that differ in the number of neu-trons they contain are known as isotopes.Because all the isotopes of an element havethe same number of electrons, they all havethe same chemical properties.

A chemical compound is a substanceformed by the chemical combination of twoor more elements in definite proportions.Atoms in compounds are held together bychemical bonds. An ionic bond is formedwhen one or more electrons are transferredfrom one atom to another. A covalent bondforms when electrons are shared betweenatoms. The structure that results whenatoms are joined together by covalent bondsis called a molecule. Unequal sharing ofelectrons creates regions of positive andnegative charges in molecules. Slight attrac-tion can develop between the oppositelycharged regions of nearby molecules. Suchintermolecular forces of attraction are calledvan der Waals forces.

2–2 Properties of WaterThe water molecule (H2O) is neutral. Yet, theoxygen end of the molecule has a slight posi-tive charge, and the hydrogen end has aslight negative charge.

A molecule in which the charges areunevenly distributed is called a polarmolecule. Polar molecules can attract eachother. The attraction between the hydrogenatom on one water molecule and the oxygenatom on another water molecule is called ahydrogen bond. Cohesion is an attractionbetween molecules of the same substance.Adhesion is an attraction between moleculesof different substances.

A mixture is a material composed of twoor more elements or compounds that arephysically mixed together—the substancesare not chemically combined. A solution is amixture in which all the components areevenly distributed throughout the mixture.In a solution, the substance that is dissolvedis called the solute. The substance in whichthe solute dissolves is called the solvent.Water is the greatest solvent on Earth.

A water molecule can react to form ions.A water molecule (H2O) can form a hydro-gen ion (H+) and a hydroxide ion (OH_). ThepH scale indicates the concentration of H+

ions in a solution. Pure water has a pH of 7.An acid is any compound that forms H+

ions in solution. Acidic solutions containhigher concentrations of H+ ions than purewater. A base is a compound that producesOH_ ions in solution. Basic, or alkaline,solutions contain lower concentrations ofH+ ions than pure water and have pH val-ues above 7.

Summary

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2–3 Carbon CompoundsOrganic chemistry is the study of all com-pounds that contain bonds between carbonatoms. Carbon compounds are also calledorganic compounds. Many of the moleculesin living things are so large that they areknown as macromolecules. Macromoleculesare formed in a process called polymerization.Smaller units, called monomers, join togetherto form macromolecules, or polymers.

Four groups of organic compoundsfound in living things are carbohydrates,lipids, nucleic acids, and proteins. Carbohy-drates are compounds made up of carbon,hydrogen, and oxygen atoms. Living thingsuse carbohydrates as their main source ofenergy. Plants and some animals use carbo-hydrates in structures. Starches and sugarsare examples of carbohydrates.

Lipids are made mostly from carbon andhydrogen atoms. Fats, oils, and waxes arelipids. Lipids are used in living things tostore energy. Some lipids are important partsof biological membranes and waterproofcoverings. Lipid molecules are made up ofcompounds called fatty acids and glycerol.

Nucleic acids contain hydrogen, oxy-gen, nitrogen, carbon, and phosphorus.Nucleotides are the monomers that makeup nucleic acids. Each nucleotide consistsof a 5-carbon sugar, a phosphate group,and a nitrogenous base. Nucleic acids storeand transmit hereditary, or genetic, infor-mation. There are two kinds of nucleicacids: ribonucleic acid (RNA) and deoxyri-bonucleic acid (DNA).

Proteins contain nitrogen as well as car-bon, hydrogen, and oxygen. Proteins arepolymers of molecules called amino acids.Some proteins control the rate of reactionsand regulate cell processes. Some are usedto form bones and muscles. Others trans-port substances into or out of cells or helpto fight disease.

2–4 Chemical Reactions andEnzymesA chemical reaction is a process thatchanges one set of chemicals (reactants) intoanother set of chemicals (products). Chemi-cal reactions always involve the breaking ofbonds in reactants and the formation of newbonds in products.

Some chemical reactions release energy,and other reactions absorb energy. Chemicalreactions that release energy often occurspontaneously. Every chemical reactionneeds energy to get started, and that startingenergy is called activation energy.

A catalyst is a substance that speeds upthe rate of a chemical reaction. Catalystswork by lowering a reaction’s activationenergy. Enzymes are proteins that act as bio-logical catalysts. Enzymes speed up chemicalreactions by lowering activation energies. Inan enzyme-catalyzed reaction, the reactantsare known as substrates. The substrates bindto a site on the enzyme called the active site.


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Section 2–1 The Nature of Matter (pages 35–39)

Key Concepts• What three subatomic particles make up atoms?

• How are all of the isotopes of an element similar?

• What are the two main types of chemical bonds?

Atoms (page 35)

1. The basic unit of matter is called a(an) .

2. Describe the nucleus of an atom.

3. Complete the table about subatomic particles.

Particle Charge Location in Atom

Positive

Neutral

Negative

SUBATOMIC PARTICLES

4. Why are atoms neutral despite having charged particles?

Elements and Isotopes (page 36)

5. What is a chemical element?

6. What does an element’s atomic number represent?

7. Atoms of the same element that differ in the number of neutrons they contain are

known as .

8. How are isotopes identified?

9. Why do all isotopes of an element have the same chemical properties?


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Chemical Compounds (page 37)

10. What is a chemical compound?

11. What does the formula for table salt indicate about that compound?

Chemical Bonds (pages 38–39)

12. What holds atoms in compounds together?

13. Complete the table about the main types of chemical bonds.

Type Formed when . . .

Covalent bond

Ionic bond

CHEMICAL BONDS

14. What is an ion?

15. Is the following sentence true or false? An atom that loses electrons has a negative

charge.

16. The structure that results when atoms are joined together by covalent bonds is called

a(an) .

17. Circle the letter of each sentence that is true about covalent bonds.

a. When atoms share two electrons, it is called a double bond.

b. In a water molecule, each hydrogen atom forms a singlecovalent bond.

c. Atoms can share six electrons and form a triple bond.

d. In a covalent bond, atoms share electrons.

18. The slight attractions that develop between oppositely charged regions of nearby molecules are called .


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Section 2–2 Properties of Water (pages 40–43)

Key Concepts• Why are water molecules polar?

• What are acidic solutions? What are basic solutions?

The Water Molecule (pages 40–41)

1. Is the following sentence true or false? A water molecule is neutral.

2. Why is a water molecule polar?

3. Circle the letter of each sentence that is true about hydrogen bonds.

a. A hydrogen bond is stronger than an ionic bond.

b. The attraction between the hydrogen atom on one watermolecule and the oxygen atom on another water molecule is anexample.

c. A hydrogen bond is stronger than a covalent bond.

d. They are the strongest bonds that form between molecules.

4. Complete the table about forms of attraction.

Form of Attraction Definition

Cohesion

Adhesion

FORMS OF ATTRACTION

Solutions and Suspensions (pages 41–42)

5. What is a mixture?

6. A mixture of two or more substances in which the molecules of the substances are

evenly mixed is called a(an) .

7. The greatest solvent in the world is .

8. What is a suspension?


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9. Complete the table about substances in solutions.

10 14

Stom

ach acid

Lemon juice

Norm

al rainfall

Pure w

ater

Hum

an blood

Seaw

ater

Soap

Bleach

2 3 4 5 6 7 8 9 10 11 12 13

Neutral

Substance Definition Saltwater Solution

Solute

Water

SUBSTANCES IN SOLUTIONS

Acids, Bases, and pH (pages 42–43)

10. Why is water neutral despite the production of hydrogen ions and hydroxide ions?

11. What does the pH scale indicate?

12. On the pH scale below, indicate which direction is increasingly acidic and which isincreasingly basic.

13. How many more H+ ions does a solution with a pH of 4 have than a solution with a

pH of 5?

14. What is an acid?

15. Is the following sentence true or false? Strong bases have pH values ranging from

11 to 14. 16. What are buffers?

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Section 2–3 Carbon Compounds (pages 44–48)

Key Concept• What are the functions of each group of organic compounds?

The Chemistry of Carbon (page 44)

1. How many valence electrons does each carbon atom have?

2. What gives carbon the ability to form chains that are almost unlimited in length?

Macromolecules (page 45)

3. Many of the molecules in living cells are so large that they are known as

.

4. What is the process called by which macromolecules are formed?

5. When monomers join together, what do they form?

6. What are four groups of organic compounds found in living things?

a.

b.

c.

d.

Carbohydrates (pages 45–46)

7. What atoms make up carbohydrates?

8. Circle the letter of each sentence that is true about carbohydrates.

a. Starches and sugars are examples of carbohydrates.

b. Living things use them as their main source of energy.

c. The monomers in sugar polymers are starch molecules.

d. Plants and some animals use them for strength and rigidity.

9. Single sugar molecules are also called .

10. Circle the letter of each monosaccharide.

a. galactose c. glucose

b. glycogen d. fructose


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11. What are polysaccharides?

12. How do plants and animals store excess sugar?

Lipids (pages 46–47)

13. What kinds of atoms are lipids mostly made of?

14. What are three common categories of lipids?

a. b. c.

15. Many lipids are formed when a glycerol molecule combines with compounds

called .

16. Circle the letter of each way that fats are used in living things.

a. As parts of biological membranes

b. To store energy

c. To give plants rigidity

d. As chemical messengers

17. Complete the table about lipids.

Kind of Lipid Description

Each carbon atom in a lipid’s fatty acid chain is joined to another carbon atom by a single bond.

Unsaturated

A lipid’s fatty acids contain more than one double bond.

LIPIDS

Nucleic Acids (page 47)

18. Nucleic acids contain what kinds of atoms?

19. The monomers that make up nucleic acids are known as .

20. A nucleotide consists of what three parts?


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21. What is the function of nucleic acids in living things?

22. What are two kinds of nucleic acids?

a.

b.

Proteins (pages 47–48)

23. Proteins contain what kinds of atoms?

24. Proteins are polymers of molecules called .

25. What are four roles that proteins play in living things?

a.

b.

c.

d.

Reading Skill PracticeYou can often increase your understanding of what you’ve read by makingcomparisons. A compare-and-contrast table helps you to do this. On a separate sheetof paper, make a table to compare the four groups of organic compounds you readabout in Section 2–3. You might use the heads Elements, Functions, and Examplesfor your table. For more information about compare-and-contrast tables, seeOrganizing Information in Appendix A.


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Section 2–4 Chemical Reactions and Enzymes (pages 49–53)

Key Concepts• What happens to chemical bonds during chemical reactions?

• How do energy changes affect whether a chemical reaction will occur?

• Why are enzymes important to living things?

Chemical Reactions (page 49)

1. What is a chemical reaction?

2. In the space provided, write a definition for each of the terms

Energy-Releasing Reaction

Ene

rgy

Course of Reaction

Definition

Reactants

Products

3. Chemical reactions always involve changes in chemical .

Energy in Reactions (page 50)

4. What is released or absorbed whenever chemical bonds form or are broken?

5. What do chemical reactions that absorb energy need to occur?

6. Chemists call the energy needed to get a reaction started the .

7. Complete the graph of an energy-releasing reaction by indicating where the energy ofthe reactants, the energy of the products, and the activation energy should appear.


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Enzymes (pages 51–52)

8. What is a catalyst?

9. Proteins that act as biological catalysts are called .

10. What do enzymes do?

11. What is part of an enzyme’s name usually derived from?

Enzyme Action (pages 52–53)

12. The reactants of enzyme-catalyzed reactions are known as .

13. Why are the active site and the substrates in an enzyme-catalyzed

reaction often compared to a lock and key?

14. The binding together of an enzyme and a substrate forms a(an)

.

15. How do most cells regulate the activity of enzymes?


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Vocabulary Review

Crossword Puzzle Use the clues below to fill in the spaces in the puzzle with the correct words.Across

1. element or compound that enters into achemical reaction

4. process that changes one set of chemi-cals into another

7. positively charged subatomic particle8. substance formed by the chemical com-

bination of two or more elements indefinite proportions

11. positively or negatively charged atom12. carbon compound that stores and trans-

mits genetic information14. the center of an atom16. bond formed when electrons are shared

between atoms17. macromolecule formed when

monomers join together

Down2. negatively charged subatomic particle3. compound that produces hydroxide

ions in solution5. bond formed when one or more elec-

trons are transferred from one atom toanother

6. monomer of nucleic acid9. monomer of protein

10. compound that forms hydrogen ions insolution

13. atom of same element that differs innumber of neutrons compared withother atoms of the element

15. basic unit of matter

7

4

14

1 2

11

5

8

16

13

17

3

12

10

15

6

9


chapter 2 the chemistry of life summary -...

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