THE PROCESS OF SCIENCE

– What is science?– The word science is derived from a Latin verb

meaning “to know.”

Discovery Science

• Science seeks natural causes for natural phenomena.

– This limits the scope of science to the study of structures and processes that we can observe and measure.

• As a formal process of inquiry, consists of a series of steps.

– The key element of the scientific method is hypothesis-driven science.

Hypothesis-Driven Science

Hypothesis-Driven Science– As a formal process of inquiry, the scientific method

consists of a series of steps.• The key element of the scientific method is

hypothesis-driven science.

Observation Question Hypothesis Prediction Experiment

Revise and repeat

Observation:My flashlightdoesn’t work.

Question:What’s wrong

with myflashlight?

Prediction:If I replace thebatteries, theflashlight will

work.

Experiment:I replace the

batteries withnew ones.

Experimentsupports

hypothesis;make additional

predictionsand test them.

Hypothesis:The flashlight’s

batteriesare dead.

Hypothesis-Driven Science

Theories in Science

– What is a scientific theory, and how is it different from a hypothesis?

• A theory is much broader in scope than a hypothesis.

• Theories only become widely accepted in science if they are supported by an accumulation of extensive and varied evidence.

Chemistry of Life– Matter is anything that occupies space and has mass.– Matter is found on the Earth in three physical states:

• Solid

• Liquid

• Gas

Atoms

Nucleus

Protons

Neutrons

Electrons

Nucleus

Cloud of negativecharge 2 electrons

2

2

2

– Each element consists of one kind of atom.• An atom is the smallest unit of matter that still retains the

properties of an element.

– Matter is composed of chemical elements.• Elements are substances that cannot be broken down

into other substances.

Chemistry of Life

Change the number of PROTONS in the nucleus and you change the ELEMENT

– Elements differ in the number of subatomic particles in their atoms.

• The number of protons, the atomic number, determines which element it is.

• An atom’s mass number is the sum of the number of protons and neutrons.

• Mass is a measure of the amount of matter in an object.

Chemistry of Life

Periodic Table of the Elements

Atomic number = number of protons within the nucleus

Other nonmetals    Halogens    

Noble gases    

Other metals    

Rare earth metals    Transition metals    

Alkali earth metals    

Alkali metals    

Synthetic      

Gas     

Liquid     

Solid    

Legend

Chemistry of Life

Carbon C: 18.5%

Hydrogen H:9.5%

Nitrogen N:3.3%

Calcium Ca: 1.5%

Trace elements: less than 0.01%

Boron B Manganese Mn

Oxygen O:65.0%

Magnesium Mg: 0.1%

Phosphorus P: 1.0%

Potassium K: 0.4%

Sulfur S: 0.3%

Sodium Na: 0.2%

Chlorine Cl: 0.2%

Cobalt CoChromium Cr

Iron FeIodine IFluorine FCopper Cu Silicon Si

Zinc ZnVanadium VTin Sn

Molybdenum MoSelenium Se

– Twenty-five elements are essential to life.– Four elements make up about 96% of the weight of

the human body:• Oxygen• Carbon• Hydrogen• Nitrogen

First electron shellcan hold 2 electrons

Outer electron shellcan hold 8 electrons

Hydrogen HAtomic number = 1

Carbon CAtomic number = 6

Nitrogen NAtomic number = 7

Oxygen OAtomic number = 8

Electron

Chemical Properties of Atoms– Electrons determine how an atom behaves when it encounters

other atoms.

© 2010 Pearson Education, Inc.

Covalent Bonds– A covalent bond forms when two atoms share one or

more pairs of outer-shell electrons.– Atoms held together by covalent bonds form a

molecule.

Namemolecular formula

Hydrogen gas H2

Oxygen gas O2

Methane CH4

Electron configuration Structural formula Space-filling model Ball-and-stick model

Single bonda pair of shared electrons

Double bondtwo pairs of shared electrons

Ionic Bonds– When an atom loses or gains electrons, it becomes

electrically charged.• Charged atoms are called ions.

• Ionic bonds are formed between oppositely charged ions.

Outer shellhas 1 electron

Outer shellhas 7 electrons

The outer electron is strippedfrom sodium and completesthe chlorine atom’s outer shell

NaSodium atom

ClChlorine atom

Completeouter shells

The attractionbetween theions—an ionicbond—holdsthem together

Na

Sodium ionCl

Chlorine ion

Sodium chloride (NaCl)

Hydrogen Bonds– Water is a compound in which the electrons in its

covalent bonds are shared unequally.• This causes water to be a polar molecule, one with opposite

charges on opposite ends.

H H

O

slightly slightly

slightly –

Hydrogen bonding

• Weak bonds formed between hydrogen and another atom – Surface tension of water

• Important as intramolecular bonds, giving shape to proteins and other biomolecules

WATER AND LIFE– Life on Earth began in water and evolved there for 3

billion years.• Modern life remains tied to water.

• Your cells are composed of 70%–95% water.

Properties of Water

• Numerous properties due to the hydrogen bonding

Properties of Water

Microscopic tubes

Cohesion due tohydrogen bondsbetween watermolecules

Evaporation from the leaves

SE

M

Flow

of

wat

er

– Water molecules stick together as a result of hydrogen bonding.

• This is called cohesion.

– Heat and temperature are related, but different.• Heat is the amount of energy associated with the movement of

the atoms and molecules in a body of matter.

• Temperature measures the intensity of heat.

– Water can absorb and store large amounts of heat while only changing a few degrees in temperature.

– Water can moderate temperatures.

Properties of Water

– Surface tension is the measure of how difficult it is to stretch or break the surface of a liquid.

• Hydrogen bonds give water an unusually high surface tension.

Properties of Water

*solution

*solvent *solute *aqueous solution

Water is the solvent of life

Basicsolution

Neutralsolution

Acidicsolution

Oven cleaner

Householdbleach

Human bloodPure water

Grapefruit juice,soft drinkLemon juice,gastric juice

Household ammonia

Milk of magnesia

Seawater

Tomato juice

Urine

pH scale0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Incr

easi

ng

ly a

cid

icg

rea

ter

H

con

cen

trat

ion

Incr

easi

ng

ly b

asic

lo

wer

H

con

cen

trat

ion

Neutral[H+] [OH–]

Acids, Bases and pH

Carbon and Organic Chemistry

– Carbon is a versatile atom.– Carbon forms large, complex, and diverse molecules

necessary for life’s functions.– Organic compounds are carbon-based molecules.

Structuralformula

Ball-and-stickmodel

Space-fillingmodel

• Variations in Carbon skeletons Carbon skeletons vary in length

Carbon skeletons may be unbranched or branched

Carbon skeletons may have double bonds,which can vary in location

Carbon skeletons may be arranged in rings

Carbon and Organic Chemistry

– Larger hydrocarbons form fuels for engines.– Hydrocarbons of fat molecules fuel our bodies.

Hydrocarbons

• The unique properties of an organic compound depend not only on its carbon skeleton but also on the atoms attached to the skeleton

– These atoms are called functional groups– Some common functional groups include:

Hydroxyl group Carbonyl group Amino group Carboxyl group

Found in alcoholsand sugars

Found in sugarsFound in amino acidsand urea in urine (fromprotein breakdown)

Found in amino acids,fatty acids, and somevitamins

Carbon and Organic Chemistry

Macromolecules– On a molecular scale, many of life’s molecules are

gigantic, earning the name macromolecules.– Three categories of macromolecules are

• Carbohydrates

• Proteins

• Nucleic acids

*most macromolecules are polymerspolymer

monomer

The making and breaking of polymers:

Dehydration reaction: Hydrolysis:

Macromolecules

• Carbohydrates include

Carbohydrates

– Small sugar molecules in soft drinks• Monosaccharides & Disaccharides

– Long starch molecules in pasta and potatoes• Polysaccharides

• Monosaccharides are simple sugars

Monosaccharides

– Glucose, found in sports drinks

– Fructose, found in fruit

• Honey contains both glucose and fructose

Glucose Fructose

Isomers

• In aqueous solutions, monosaccharides form rings

(a) Linear and ring structures

(b) Abbreviated ring structure

Monosaccharides

• A disaccharide is a double sugar

Disaccharides

• Disaccharides are joined by the process of dehydration synthesis

Glucose Glucose

Maltose

• The most common disaccharide is sucrose, common table sugar

– It consists of a glucose linked to a fructose

– Sucrose is extracted from sugar cane and the roots of sugar beets

Disaccharides

Polysaccharides

(a) Starch

Starch granules inpotato tuber cells

Glucosemonomer

(b) Glycogen

GlycogenGranulesIn muscletissue

(c) Cellulose

Cellulose molecules

Cellulose fibril ina plant cell wall

– They are long chains of sugar units

– They are polymers of monosaccharides

• Most animals cannot derive nutrition from fiber

– How do grazing animals survive on a diet of cellulose?

Polysaccharides

Proteins• Proteins perform most of the tasks the body

needs to function– They are the most elaborate of life’s molecules

MAJOR TYPES OF PROTEINS

Structural Proteins Storage Proteins Contractile Proteins Transport Proteins Enzymes

• All proteins are constructed from a common set of 20 kinds of amino acids

The Monomers: Amino Acids

Aminogroup

Carboxylgroup

Sidegroup

Carboxylgroup

Aminogroup

Sidegroup

Sidegroup

Amino acid Amino acid

Dehydrationsynthesis

Sidegroup

Sidegroup

Peptide bond

• Cells link amino acids together by dehydration synthesis

Proteins as Polymers

– The resulting bond between them is called a peptide bond

• Primary structure

– The specific sequence of amino acids in a protein

1 510 15

20253035

4045

5055

6065

70

75 80 85

9095

100

105110 115

120125

129

Amino acid

– The arrangement of amino acids makes each protein different

Protein Structure

• A slight change in the primary structure of a protein affects its ability to function

– The substitution of one amino acid for another in hemoglobin causes sickle-cell disease

(a) Normal red blood cell Normal hemoglobin

12 3

4 56

7. . . 146

(b) Sickled red blood cell Sickle-cell hemoglobin

2 314 5

67. . . 146

Protein Structure

• Proteins have four levels of structure

Hydrogen bond

Pleated sheet

Amino acid

(a) Primary structure

Hydrogen bond

Alpha helix

(b) Secondary structure

Polypeptide(single subunit)

(c) Tertiary structure

Completeprotein,with fourpolypeptidesubunits

(d) Quaternary structure

Protein Structure