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Lectures by Chris C. Romero, updated by Edward J. Zalisko

PowerPoint® Lectures forCampbell Essential Biology, Fourth Edition – Eric Simon, Jane Reece, and Jean DickeyCampbell Essential Biology with Physiology, Third Edition – Eric Simon, Jane Reece, and Jean Dickey

Chapter 2Chapter 2

Essential Chemistry for Biology

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Matter: Elements and Compounds

• Matter is anything that occupies space and has mass.

• Matter is found on the Earth in three physical states:

– Solid

– Liquid

– Gas

• Matter is composed of chemical elements.

– Elements are substances that cannot be broken down into other substances.

– There are 92 naturally occurring elements on Earth.

• All of the elements are listed in the periodic table.

H

Rb

K

Na

Li

Fr

Cs

Sr

Ca

Mg

Be

Ra

Ba

Y

Sc

Ac

La

Zr

Ti

Rf

Hf

Nb

V

Db

Ta

Mo

Cr

Sg

W

Tc

Mn

Bh

Re

Ru

Fe

Hs

Os

Rh

Co

Mt

Ir

Pd

Ni

Uun

Pt

Xe

Kr

Uuo

Rn

Ag

Cu

Uuu

Au

Cd

Zn

Uub

Hg

Ar

Ne

In

Ga

Tl

Al

B

Sn

Ge

Uuq

Pb

Si

C

Sb

As

Bi

P

N

Te

Se

Uuh

Po

S

O

I

Br

At

Cl

F

He

Th

Ce

Pa

Pr

U

Nd

Np

Pm

Pu

Sm

Am

Eu

Lr

Lu

Cm

Gd

Bk

Tb

Cf

Dy

Es

Ho

Fm

Er

Md

Tm

No

Yb

6

C12

Figure 2.1

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• Twenty-five elements are essential to life.

• Four elements make up about 96% of the weight of the human body:

– Oxygen

– Carbon

– Hydrogen

– Nitrogen

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

Figure 2.2

Figure 2.3

Lack of iodine can cause goiter

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• Elements can combine to form compounds.

– Compounds are substances that contain two or more elements in a fixed ratio.

– Common compounds include

– NaCl (table salt)

– H2O (water)

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Atoms

• Each element consists of one kind of atom.

– An atom is the smallest unit of matter that still retains the properties of an element.

• Atoms are composed of subatomic particles.

– A proton is positively charged.

– An electron is negatively charged.

– A neutron is electrically neutral.

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Proton• Positive charge• Determines element

Neutron• No charge• Determines isotope

Electron• Negative charge• Participates in chemical reactions• Outer-shell electrons determine chemical behavior

Nucleus• Consists of neutrons and protons

Atom

Figure UN2-5

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• 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.

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

Figure 2.5

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Chemical Bonding and Molecules

• Chemical reactions enable atoms to give up or acquire electrons to complete their outer shells.

• Chemical reactions usually result in atoms

– Staying close together

– Being held together by chemical 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)

Figure 2.6-2

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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.

• The number of covalent bonds an atom can form is equal to the number of additional electrons needed to fill its outer shell.

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

Figure 2.7

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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 –Figure UN2-2

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• The polarity of water results in weak electrical attractions between neighboring water molecules.

– These interactions are called hydrogen bonds.

Hydrogen bond

Figure 2.8

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Water’s Life-Supporting Properties

• The polarity of water molecules and the hydrogen bonding that results explain most of water’s life-supporting properties.

– Water molecules stick together.

– Water has a strong resistance to change in temperature.

– Frozen water floats.

– Water is a common solvent for life.

Microscopic tubes

Cohesion due tohydrogen bondsbetween watermolecules

Evaporation from the leaves

SE

M

Flow

of

wat

er

Figure 2.10

Figure 2.11

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• 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.

– Earth’s giant water supply causes temperatures to stay within limits that permit life.

– Evaporative cooling removes heat from the Earth and from organisms.

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The Biological Significance of Ice Floating

• When water molecules get cold enough, they move apart, forming ice.

• A chunk of ice has fewer molecules than an equal volume of liquid water.

• Ice floats because it is less dense than the liquid water around it.

• If ice did not float, ponds, lakes, and even the oceans would freeze solid.

• Life in water could not survive if bodies of water froze solid.

Hydrogen bond

Liquid water Ice

Figure 2.13

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Water as the Solvent of Life

• A solution is a liquid consisting of a homogeneous mixture of two or more substances.

– The dissolving agent is the solvent.

– The dissolved substance is the solute.

• When water is the solvent, the result is an aqueous solution.

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Acids, Bases, and pH

• A chemical compound that releases H+ to solution is an acid.

• A compound that accepts H+ and removes it from solution is a base.

• Buffers are substances that resist pH change.

• Buffers

– Accept H+ ions when they are in excess

– Donate H+ ions when they are depleted

• Increases in global CO2 concentrations may lead to the acidification of the oceans.

• To describe the acidity of a solution, chemists use the pH scale.

Basicsolution

Neutralsolution

Acidicsolution

Oven cleaner

Householdbleach

Human bloodPure water

Grapefruit juice,soft drink

Lemon 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 c

on

cen

trat

ion

Incr

easi

ng

ly b

asic

lo

wer

H c

on

cen

trat

ion

Neutral[H+] [OH–]

Figure 2.16