The Chemical Basis of Life

1. CHAPTER 2
THE
CHEMICAL
BASIS OF LIFE
• COPYRIGHT © MCGRAW-HILL EDUCATION. ALL RIGHTS RESERVED. AUTHORIZED ONLY FOR INSTRUCTOR USE IN THE CLASSROOM. NO REPRODUCTION OR DISTRIBUTION WITHOUT THE PRIOR WRITTEN CONSENT OF MCGRAW-HILL EDUCATION.

2. 2.1
ATOMS
AND
ATOMIC
BONDS
• IN THIS SECTION, THE FOLLOWING
OBJECTIVES WILL BE COVERED:
• DISTINGUISH AMONG THE TYPES,
LOCATIONS AND CHARGES OF
SUBATOMIC PARTICLES.
• CONTRAST IONIC AND COVALENT BONDS.
• IDENTIFY THE REACTANTS AND PRODUCTS
IN A CHEMICAL EQUATION.

3. MATTER
• REFERS TO ANYTHING THAT TAKES UP
SPACE AND HAS MASS
• CAN EXIST AS A SOLID, LIQUID, OR GAS
• COMPOSED OF ELEMENTS
• ELEMENT—SUBSTANCE THAT CANNOT BE
BROKEN DOWN INTO ANOTHER
SUBSTANCE BY ORDINARY CHEMICAL
MEANS
• ONLY 92 NATURALLY OCCURRING
ELEMENTS
• FOUR ELEMENTS MAKE UP ABOUT 96%
OF THE BODY WEIGHT OF MOST LIVING
ORGANISMS—CARBON, HYDROGEN,
OXYGEN, AND NITROGEN

4. ELEMENTS IN
LIVING
ORGANISMS
(PHOTO): © BRAND X PICTURES/PUNCHSTOCK RF

5. ATOMIC
STRUCTURE
Atomic theory states that elements consist of atoms
• H for hydrogen or Na for sodium
Atomic symbol—name of the atom or element
• Neutrons—no electrical charge, found in nucleus
• Protons—positive charge, found in nucleus
• Electrons—negative charge, found outside of nucleus
Subatomic parts
• Mass is the number of protons plus neutrons
(electrons have no mass)
• Atomic weight changes with gravity
Mass number vs. Atomic weight

6. TWO MODELS OF HELIUM (HE)

7. ATOMIC NUMBER
• ALL ATOMS OF AN ELEMENT HAVE
THIS SAME NUMBER OF PROTONS
• ALSO GIVES NUMBER OF
ELECTRONS IF AN ATOM IS
ELECTRICALLY NEUTRAL

8. THE PERIODIC TABLE
• ELEMENTS’ CHEMICAL AND PHYSICAL
CHARACTERISTICS RECUR IN A PREDICTABLE MANNER
• ATOMS ARE ARRANGED IN PERIODS (ROWS) AND
GROUPS (COLUMNS)
• ELEMENTS ARE LISTED IN ORDER OF ATOMIC NUMBER

9. ISOTOPES
Radioactive isotope behavior is essentially the
same as a stable isotope of same element
Can be used as
tracer—PET
scan
Can cause
damage to cells,
leading to
cancer
Can be used to
sterilize medical
equipment
Unstable and may decay, emitting
harmful radiation
Isotopes have the same number of
protons but a different number of
neutrons (different mass numbers)

10. PET SCANS USE ISOTOPES
© NATIONAL INSTITUTES OF HEALTH

11. HIGH
LEVELS OF
RADIATION
A: © DIGITALGLOBE/GETTY
IMAGES; B: © GETTY IMAGES

12. ARRANGEMENT
OF ELECTRONS
IN AN ATOM
Electrons are constantly moving,
forming a negative “cloud”
around the nucleus
Models of atoms are typically
constructed with energy levels or
electron shells
• 2 electrons fill first shell
• 8 electrons fill each additional shell
Each shell contains a certain
number of electrons.; for atoms
up through number 20:

13. ATOM STABILITY AND THE
VALENCE SHELL
• OCTET RULE FOR VALENCE SHELL
• VALENCE SHELL—OUTERMOST SHELL
• IF AN ATOM HAS MORE THAN 2 SHELLS, THE
OUTER SHELL IS MOST STABLE WITH 8
ELECTRONS
• ATOMS CAN GIVE UP, ACCEPT, OR SHARE
ELECTRONS TO HAVE 8
• CHEMICAL PROPERTIES OF ATOMS ARE
LARGELY DETERMINED BY THE
ARRANGEMENT OF THEIR ELECTRONS.

14. ATOMS OF THE SIX MOST
IMPORTANT ELEMENTS FOR LIFE

15. CHEMICAL BONDS
• MOLECULE—GROUP OF ATOMS BONDED TOGETHER
• O2, H2O, C6H12O6, N2
• COMPOUND—MOLECULE CONTAINING ATOMS OF
MORE THAN ONE ELEMENT
• H2O, C6H12O6
• 2 TYPES OF BONDS
• IONIC—ATTRACTION BETWEEN OPPOSITE CHARGES
• COVALENT—SHARING ELECTRONS TO COMPLETE OUTER SHELL

16. IONIC BONDS
• FORMS WHEN 2 ATOMS ARE HELD TOGETHER BY
THE ATTRACTION BETWEEN OPPOSITE CHARGES
• SODIUM HAS 1 ELECTRON IN VALENCE SHELL
• USUALLY GIVES UP AN ELECTRON
• CHLORINE HAS 7 ELECTRONS IN VALENCE SHELL
• USUALLY ACCEPTS AN ELECTRON FROM
ANOTHER ATOM
• IONS—CHARGED ATOMS
• SODIUM HAS 1 MORE PROTON THAN
ELECTRONS: NOW NA+
• CHLORINE HAS 1 MORE ELECTRON THAN
PROTONS: NOW CL−
• IONIC COMPOUNDS ARE OFTEN CALLED SALTS

17. FORMATION
OF SODIUM
CHLORIDE

18. COVALENT BONDS
• 2 ATOMS SHARE ELECTRONS
• 2 HYDROGEN ATOMS CAN SHARE
ELECTRONS TO FILL THEIR OUTER
SHELL—ORBITALS OVERLAP.
• STRUCTURAL FORMULA—USES
STRAIGHT LINES H-H
• 1 LINE INDICATES 1 PAIR OF SHARED
ELECTRONS.
• MOLECULAR FORMULA—SIMPLY
SHOWS NUMBER OF ATOMS
INVOLVED H2

19. • 2 ATOMS SHARE 4
ELECTRONS
• DOUBLE BONDS ARE
STRONGER THAN
SINGLE BONDS
• TRIPLE BONDS CAN
ALSO FORM AND ARE
THE STRONGEST
DOUBLE COVALENT BONDS

20. MOLECULAR
MODELS
METHANE 𝐂𝐇 𝟒
A. ELECTRON MODEL
SHOWING COVALENT BONDS
B. STRUCTURAL MODEL
C. BALL-AND-STICK MODEL
D. SPACE-FILLING MODEL

21. • SHOW THE TYPE AND
NUMBER OF ATOMS IN
A MOLECULE
• MOLECULAR FORMULA
FOR GLUCOSE
MOLECULAR FORMULAS

22. CHEMICAL
REACTIONS
Equation is balanced if the same number
of each type of atom occurs on both
sides of the arrow.
Reactants—molecules that participate in
chemical reactions
• Shown to the left of the arrow
Products—molecules formed by reactions
• Shown to the right of the arrow
An overall equation for photosynthesis:
6CO2
CARBON DIOXIDE
+
6H2O
WATER
→
C6H12O6
GLUCOSE
+
6O2
OXYGEN

23. 2.2 WATER’S
IMPORTANCE
TO LIFE
• IN THIS SECTION, THE FOLLOWING
OBJECTIVES WILL BE COVERED:
• DESCRIBE THE GENERAL STRUCTURE OF A
WATER MOLECULE.
• LIST AND DEFINE THE PROPERTIES OF
WATER THAT ARE IMPORTANT TO LIFE.

24. WATER
• LIFE BEGAN IN WATER
• SINGLE MOST IMPORTANT MOLECULE
ON EARTH
• ALL ORGANISMS ARE 70–90% WATER
• WATER HAS UNIQUE PROPERTIES THAT
MAKE IT A LIFE-SUPPORTING SUBSTANCE
• PROPERTIES STEM FROM THE STRUCTURE
OF THE MOLECULE

25. WATER’S STRUCTURE
• POLAR COVALENT BOND
• ATOMS DO NOT SHARE ELECTRONS EQUALLY.
• OXYGEN IS MORE ELECTRONEGATIVE THAN
HYDROGEN.
• ELECTRONS SPEND MORE TIME AROUND THE
OXYGEN NUCLEUS THAN THE HYDROGEN
NUCLEI.
• OXYGEN END BECOMES SLIGHTLY
NEGATIVE/HYDROGENS BECOME SLIGHTLY
POSITIVE—NOT AN IONIC BOND OR IONS
• HYDROGEN BOND—SLIGHTLY POSITIVE
HYDROGEN OF ONE WATER MOLECULE ATTRACTED
TO THE SLIGHTLY NEGATIVE OXYGEN IN ANOTHER
WATER MOLECULE
This Photo by Unknown Author is licensed under CC BY-SA-NC

26. THE
STRUCTURE
OF WATER

27. PROPERTIES
OF WATER:
OVERVIEW
Solvency
Cohesion and adhesion
High surface tension
High heat capacity
High heat of vaporization
Varying density

28. • WATER IS KNOWN AS THE “UNIVERSAL SOLVENT”
• DUE TO POLARITY AND H-BONDING, WATER HAS THE ABILITY TO
DISSOLVE MANY SUBSTANCES
• HYDROPHILIC—MOLECULES ATTRACTED TO WATER
• HYDROPHOBIC—MOLECULES NOT ATTRACTED TO WATER
• WATER CAUSES NACL TO DISSOCIATE
PROPERTIES OF WATER: SOLVENCY

29. PROPERTIES OF WATER:
COHESION AND ADHESION
• COHESION: ABILITY OF WATER MOLECULES
TO CLING TO EACH OTHER DUE TO
HYDROGEN BONDING
• ADHESION: ABILITY OF WATER MOLECULES
TO CLING TO OTHER POLAR SURFACES
• ALLOWS WATER TO BE AN EXCELLENT
TRANSPORT SYSTEM BOTH INSIDE AND
OUTSIDE OF LIVING ORGANISMS
• CONTRIBUTES TO WATER TRANSPORT IN
PLANTS (CAPILLARY ACTION)
This Photo by Unknown Author is licensed under CC BY-SA

30. COHESION AND ADHESION OF WATER
MOLECULES IN LIVING THINGS
(TREE): © PAUL DAVIES/ALAMY; (MAN): © ASIASELECTS/GETTY RF

31. • WATER MOLECULES AT THE
SURFACE CLING MORE
TIGHTLY TO EACH OTHER
THAN TO THE AIR ABOVE
• MAINLY DUE TO HYDROGEN
BONDING (COHESION)
• CREATES A “FILM” ON THE
WATER’S SURFACE
PROPERTIES OF WATER:
HIGH SURFACE TENSION
© MARTIN SHIELDS/ALAMY

32. PROPERTIES OF WATER: HEAT CAPACITY
AND HEAT OF VAPORIZATION
• WATER HAS A HIGH HEAT CAPACITY (ABILITY TO STORE ENERGY)
• THE MANY HYDROGEN BONDS LINKING WATER MOLECULES ALLOW WATER
TO ABSORB HEAT WITHOUT GREATLY CHANGING ITS TEMPERATURE
• TEMPERATURE OF WATER RISES AND FALLS SLOWLY
• HEAT OF VAPORIZATION IS VERY HIGH
• TAKES A GREAT DEAL OF ENERGY TO BREAK H BONDS FOR EVAPORATION
• HEAT IS DISPELLED AS WATER EVAPORATES

33. HEAT CAPACITY
AND HEAT OF
VAPORIZATION
A: © JILL BRATTEN/MCGRAW-HILL EDUCATION; B: © CLERKENWELL/GETTY RF
• WATER TAKES A LARGE AMOUNT
OF HEAT TO VAPORIZE AT 100
DEGREES CELSIUS, WHICH IS WHY
IT TAKES A LONG TIME TO BOIL
WATER.
• AS WATER EVAPORATES, IT
DISPELS HEAT ENERGY, WHICH IS
WHY WE FEEL COOLER AS OUR
SWEAT EVAPORATES OFF OUR
SKIN.

34. PROPERTIES OF WATER:
VARYING DENSITY
• ICE (SOLID) IS LESS DENSE THAN
LIQUID WATER
• UNLIKE OTHER SUBSTANCES, WATER
EXPANDS AS IT FREEZES
• THEREFORE, ICE FLOATS RATHER THAN SINKS.
• IT MAKES LIFE POSSIBLE IN WATER
• ICE ACTS AS AN INSULATOR

35. DENSITY OF ICE VS. WATER

36. 2.3
ACIDS
AND
BASES
• IN THIS SECTION, THE FOLLOWING
OBJECTIVE WILL BE COVERED:
• DISTINGUISH BETWEEN AN ACID AND A
BASE USING THE PH SCALE.

37. THE DISSOCIATION OF WATER
• WATER DISSOCIATES INTO AN EQUAL NUMBER OF
HYDROGEN IONS (H+) AND HYDROXIDE IONS (OH−)
H − O − H
WATER
⇄
H+
HYDROGEN
ION
+
OH−
HYDROXIDE
ION
This Photo by Unknown Author is licensed under CC BY

38. ACIDIC SOLUTIONS:
HIGH 𝐇+
CONCENTRATION
Acids are substances that release
hydrogen ions
Examples: lemon juice, vinegar, and coffee
HCl
HYDROCHLORIC
ACID
→
H+
HYDROGEN
ION
+
Cl−
CHLORIDE
ION

39. BASIC SOLUTIONS: LOW 𝐇+
CONCENTRATION
Bases are substances that either take up
hydrogen ions or release hydroxide ions
Examples: milk of magnesia and ammonia
NaOH
SODIUM
HYDROXIDE
→
Na+
SODIUM
ION
+
OH−
HYDROXIDE
ION

40. • MATHEMATICAL WAY TO
INDICATE THE NUMBER OF
HYDROGEN IONS IN
SOLUTION
• PH SCALE RANGES FROM
0 TO 14
• PH BELOW 7 IS ACIDIC—
MORE [H+] THAN [OH−]
• PH ABOVE 7 IS BASIC—
MORE [OH−] THAN [H+]
• PH OF 7 IS NEUTRAL—[H+]
EQUAL TO [OH−]
THE PH SCALE

41. BUFFERS AND PH
• CHEMICAL OR COMBINATION OF
CHEMICALS THAT KEEPS PH WITHIN
NORMAL LIMITS
• RESISTS PH CHANGE BY TAKING UP
EXCESS H+ OR OH−
• PH OF BLOOD IS ABOUT 7.35 – 7.45 AND
IS MAINTAINED BY BUFFER

42. ACIDOSIS
CENTRAL NERVOUS
SYSTEM
•SLEEPINESS AND
LOSS OF
CONSCIOUSNESS
•CONFUSION
•HEADACHE
•COMA
MUSCULAR
•WEAKNESS
INTESTINAL
• DIARRHEA
RESPIRATORY
•COUGHING AND
SHORTNESS OF
BREATH
HEART
•ARRHYTHMIA
•INCREASED HEART
RATE
GASTRIC
•NAUSEA
•VOMITING

43. CHAPTER 2
OBJECTIVE
SUMMARY
• YOU SHOULD NOW BE ABLE TO:
• 1. DISTINGUISH AMONG THE TYPES,
LOCATIONS AND CHARGES OF SUBATOMIC
PARTICLES.
• 2. CONTRAST IONIC AND COVALENT BONDS.
• 3. IDENTIFY THE REACTANTS AND PRODUCTS
IN A CHEMICAL EQUATION.
• 4. DESCRIBE THE GENERAL STRUCTURE OF A
WATER MOLECULE.
• 5. LIST AND DEFINE THE PROPERTIES OF WATER
THAT ARE IMPORTANT TO LIFE.
• 6. DISTINGUISH BETWEEN AN ACID AND A
BASE USING THE PH SCALE.