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
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
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