Ch 2 Essential Chemistry for Biology

8/21/2019 Ch 2 Essential Chemistry for Biology

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Chapter 2Chapter 2Essential Chemistry for Biology


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SOME BASIC CHEMISTRY

• Take any biological system apart, and you

eventually end up at the chemical level.

• Chemical reactions are always occurring in the

human body.

© 2013 Pearson Education, Inc.


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Matter: Elements and Compounds

• Matter is anything that occupies space and has

mass.

• Matter is found on Earth in three physical states:

– solid,

– liquid, and

– gas.



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• Matter is composed of chemical elements.

– n element is a substance that cannot be broken

down into other substances by chemical reactions

– There are !" naturally occurring elements on

Earth.

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




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#igure ".$a

Atomic number

(number of protons)

Mass number

(number of

protons plus neutrons)

Element symbol

12

6

C

He

Ne

Se Br

Cl

F

Ar

r

!e

"NCB

S#SiAl

$

%e As%a

&eSbSn$n

MnCr

#o At 'n#b Bi&$

CoFe CuNi n

&m *b +uHo Er ,y

Be+i

M-Na

ScCa &i

MoNb 'u&c #.'/ A- *Sr 'b r

H

C.

+aBa &aHf "s'e $r 0 Au#t H-Cs

B/S- MtHs '-,s CnFr Ac'a 'f ,b

M. No +r Es FmCf Am Cm BNp #u

Eu %. &b#m SmN.

#a

#r

&/

Ce


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• Twenty%five elements are essential to people.

• #our elements make up about !&' of the weight of

most cells:

– o(ygen,

– carbon,

– hydrogen, and

– nitrogen.




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#igure "."

"3y-en (")46578

Carbon (C)4 1958

Calcium (Ca)4 158

Ma-nesium (M-)4 718

C/lorine (Cl)4 728

So.ium (Na)4 728

Sulfur (S)4 7:8

#otassium ()4 7;8

#/osp/orus (#)4 178

Hy.ro-en (H)4


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• &race elements are

– required in only very small amounts and

– essential for life.

•

n iodine deficiency causes goiter.• #luorine

– is added to dental products and drinking water and

–helps to maintain healthy bones and teeth.




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#igure ".)


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• Elements can combine to form compounds.

– Compoun.s are substances that contain two or

more elements in a fi(ed ratio.

– Common compounds include

– *aCl +table salt and

– -" +water.




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Atoms

• Each element consists of one kind of atom.

– n atom is the smallest unit of matter that still

retains the properties of an element.



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The Structure of Atoms

• toms are composed of subatomic particles.

– proton is positively charged.

– n electron is negatively charged.

– neutron is electrically neutral.

• Most atoms have protons and neutrons packed

tightly into the nucleus.

– The nucleus is the atom/s central core.

– Electrons orbit the nucleus.


"


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#igure ".0

Nucleus 2e =

Electron clou.

Nucleus

Electrons

Neutrons

#rotons

2

2

2


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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.

–Mass is a measure of the amount of material inan ob1ect.

– n atom/s mass number is the sum of the

number of protons and neutrons in its nucleus.

The Structure of Atoms



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Isotopes

• $sotopes are alternate mass forms of an element.

• 2sotopes

– have the same number of protons and electrons

but

– differ in their number of neutrons.


T bl " $


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Table ".$


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• The nucleus of a ra.ioacti>e isotope decays

spontaneously, giving off particles and energy.

• 3adioactive isotopes have many uses in research

and medicine.

–They can be used to determine the fate of atoms in

living organisms.

– They are used in 4ET scans to diagnose heart

disorders and some cancers.

Isotopes



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• 5ncontrolled e(posure to radioactive isotopes can

harm living organisms by damaging 6*.

– The $!7& Chernobyl nuclear accident released

large amounts of radioactive isotopes.

– *aturally occurring radon gas may cause lung

cancer.

Isotopes



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Electron Arrangement and the Chemical Properties

of Atoms

•

f the three subatomic particles, only electrons aredirectly involved in the chemical activity of an atom.

• Electrons orbit the nucleus of an atom in specific

electron shells.

• The farther an electron is from the nucleus, the

greater its energy.

• The number of electrons in the outermost shell

determines the chemical properties of an atom.


#igure " &


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#igure ".&

Electron

First electron s/ell

(can /ol. 2 electrons)"uter electron s/ell

(can /ol. 9 electrons)

Hy.ro-en (H)

Atomic number 1

Carbon (C)

Atomic number 6

Nitro-en (N)

Atomic number ?

"3y-en (")

Atomic number 9

#igure " &a


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#igure ".&a

Electron

First electron s/ell


"uter electron s/ell


Hy.ro-en (H)

Atomic number 1

Carbon (C)

Atomic number 6

#igure " &b


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#igure ".&b

Nitro-en (N)

Atomic number ?

"3y-en (")

Atomic number 9


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Chemical Bonding and Molecules

• Chemical reactions enable atoms to give up or

acquire electrons, completing their outer shells.

• Chemical reactions usually result in atoms

– staying close together and

– being held together by attractions called c/emical

bon.s.



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Ionic Bonds

• 8hen an atom loses or gains electrons, it becomes

electrically charged.

– Charged atoms are called ions.

– $onic bon.s are formed between oppositely

charged ions.

#igure ".9%"


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#igure ".9 "

Completeouter s/ells

So.ium c/lori.e (NaCl)

Cl =

C/lori.e ion

Na Cl =

Na

So.ium atom

Cl

C/lorine atom

Na Cl

Na

So.ium ion


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Covalent Bonds

• co>alent bon. forms when two atoms share oneor more pairs of outer%shell electrons.

• Covalent bonds are the strongest of the variousbonds.

•

Covalent bonds hold atoms together in a molecule.• The number of covalent bonds an atom can form is

equal to the number of additional electrons neededto fill its outer shell.

#igure ".7


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g

Electron confi-uration Structural formula

Hy.ro-en -as (H2)

Space@fillin- mo.el

"3y-en -as ("2)

Met/ane (CH;)

H H

H

" "

H

H HC

Ball@an.@stic mo.el


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Hydrogen Bonds

• 8ater is a compound in which the electrons in its

covalent bonds are not shared equally.

– This causes water to be a polar molecule, one

with an uneven distribution of charge.

#igure ".5*"


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g

"

H H(sli-/tly ) (sli-/tly )

(sli-/tly )

H d B d


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• The polarity of water results in weak electrical

attractions between neighboring water molecules.

– These weak attractions are called /y.ro-en

bon.s.

Hydrogen Bonds


#igure ".!


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Hy.ro-en bon.

Sli-/tlypositi>ec/ar-e

Sli-/tlyne-ati>ec/ar-e


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Chemical Reactions

• Cells constantly rearrange molecules by breaking

e(isting chemical bonds and forming new ones.

– ;uch changes in the chemical composition of

matter are called c/emical reactions.

– simple e(ample is the reaction between o(ygen

gas and hydrogen gas that forms water.


#igure ".5*)


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'eactants

2 H2"

"3y-en

-as

Hy.ro-en

-as

#ro.ucts

0ater

2 H2 "2<

Ch i l R ti


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• Chemical reactions include

– reactants, the starting materials, and

– pro.ucts, the end materials.

• Chemical reactions

– can rearrange matter

– but cannot create or destroy matter.

Chemical Reactions


ATER A!" #I$E


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ATER A!" #I$E

• =ife on Earth began in water and evolved there for

) billion years.

– Modern life remains tied to water.

– >our cells are composed of 9?!@' water.

• The abundance of water is a ma1or reason Earth is

habitable.



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ater%s #i&e'Supporting (roperties

• The polarity of water molecules and the hydrogen

bonding that results e(plain most of water/s life%

supporting properties.

– 8ater molecules stick together.

–8ater has a strong resistance to change intemperature.

– #roAen water floats.

–8ater is a common solvent for life.


Th C h i f W


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The Cohesion of Water

• 8ater molecules stick together as a result of

hydrogen bonding.

– This tendency of molecules of the same kind to

stick together is called co/esion.

– Cohesion is vital for the transport of water from the

roots to the leaves of plants.

#igure ".$$


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Co/esion .ue to/y.ro-en bon.sbeteen ater molecules

Microscopic [email protected] tubes

C o

l o r i e .

S E

M

E>aporation from t/e lea>es

F l o

B o

f B

a t e

r



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• ;urface tension is the measure of how difficult it is

to stretch or break the surface of a liquid.

– -ydrogen bonds give water an unusually high

surface tension.



#igure ".$"


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H W t d t T t


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How Water oderates Temperature

• Because of hydrogen bonding, water has a strong

resistance to temperature change.

• -eat and temperature are related, but different.

– Heat is the amount of energy associated with the

movement of the atoms and molecules in a body ofmatter.

– &emperature measures the intensity of heat.

•8ater can absorb and store large amounts of heatwhile only changing a few degrees in temperature.




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• 8ater can moderate temperatures.

– Earth/s giant water supply causes temperatures to

stay within limits that permit life.

– E>aporati>e coolin- occurs when a substance

evaporates and the surface of the liquid remaining

behind cools down.



#igure ".$)


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The Biological Significance of Ice !loating


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• 8hen water molecules get cold enough, they move

apart, forming ice.

• chunk of ice has fewer water molecules than an

equal volume of liquid water.

• 2ce floats because it is less dense than liquid water.


#igure ".$0


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Stable /y.ro-en bon.s/ol. molecules apartDmain- ice less .enset/an ater

Hy.ro-en bon.

$ceHy.ro-en bon.s

constantly breaan. re@form

+iui. ater



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• 2f ice did not float, ponds, lakes, and even the

oceans would freeAe solid.

• =ife in water could not survive if bodies of water

froAe solid.



Water as the Solvent of "ife


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Water as the Solvent of "ife

• solution is a liquid consisting of a homogeneous

mi(ture of two or more substances.

– The dissolving agent is the sol>ent.

–The dissolved substance is the solute.

• 8hen water is the solvent, the result is an

aueous solution.


#igure ".$@


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C/lori.e ionin solution

So.ium ion

in solution

Salt crystal

Na Cl =

Na Cl =

Acids Bases and pH


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Acids) Bases) and pH

• chemical compound that releases -


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"H

"H

"H"H

"H

"HH

H

"H

"H"H

"H H

H H

H

"H"H H H

H H

H H

H G "HG

">en cleaner

Mil of ma-nesia

House/ol. ammonia

House/ol.bleac/

Seaater

&omato uice

Blac coffee

rine

#ure ater

Human bloo.

+emon uiceDstomac/ aci.Battery aci.

%rapefruit uiceDsoft .rin

pH scale

7

1

2

:

;

5

6

?

9

<

17

11

12

1:

+ o B e r H

c o n c e n t r a

t i o n

% r e a t e r H

c o n c e n

t r a t i o n

Basicsolution

Neutralsolution

Aci.icsolution

#igure ".$9a


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"H

"H

"H

"H

"H

"H

H

H

Basicsolution

"H

"H

"H"H

H

H H

H "H

"HH

H

H

H

H

H

Neutralsolution

Aci.icsolution

Acids) Bases) and pH


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• Buffers are substances that resist p- change.

• Buffers

– accept -


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Ch 2 Essential Chemistry for Biology

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