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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.
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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.
Matter: Elements and Compounds
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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.
Matter: Elements and Compounds
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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.
Matter: Elements and Compounds
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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.
Matter: Elements and Compounds
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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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"
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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.
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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.
© 2013 Pearson Education, Inc.
#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
(can /ol. 2 electrons)
"uter electron s/ell
(can /ol. 9 electrons)
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
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#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.
© 2013 Pearson Education, Inc.
#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
© 2013 Pearson Education, Inc.
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.
© 2013 Pearson Education, Inc.
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
The Cohesion of Water
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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.
The Cohesion of Water
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#igure ".$"
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H W t d t T t
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How Water oderates Temperature
• Because of hydrogen bonding, water has a strong
resistance to temperature change.
• -eat and temperature are related, but different.
– Heat is the amount of energy associated with the
movement of the atoms and molecules in a body ofmatter.
– &emperature measures the intensity of heat.
•8ater can absorb and store large amounts of heatwhile only changing a few degrees in temperature.
© 2013 Pearson Education, Inc.
How Water oderates Temperature
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• 8ater can moderate temperatures.
– Earth/s giant water supply causes temperatures to
stay within limits that permit life.
– E>aporati>e coolin- occurs when a substance
evaporates and the surface of the liquid remaining
behind cools down.
How Water oderates Temperature
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#igure ".$)
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The Biological Significance of Ice !loating
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The Biological Significance of Ice !loating
• 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.
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#igure ".$0
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Stable /y.ro-en bon.s/ol. molecules apartDmain- ice less .enset/an ater
Hy.ro-en bon.
$ceHy.ro-en bon.s
constantly breaan. re@form
+iui. ater
The Biological Significance of Ice !loating
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• 2f ice did not float, ponds, lakes, and even the
oceans would freeAe solid.
• =ife in water could not survive if bodies of water
froAe solid.
The Biological Significance of Ice !loating
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Water as the Solvent of "ife
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Water as the Solvent of "ife
• solution is a liquid consisting of a homogeneous
mi(ture of two or more substances.
– The dissolving agent is the sol>ent.
–The dissolved substance is the solute.
• 8hen water is the solvent, the result is an
aueous solution.
© 2013 Pearson Education, Inc.
#igure ".$@
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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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