The Chemical Basis of Life
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Transcript of The Chemical Basis of Life
The Chemical Basis of LifeEnergy levels of electrons
Electron configuration and chemical properties:
*chemical behavior due to
electrons
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• Numerous properties due to the hydrogen bonding
Properties of Water
Microscopic tubesCohesion due tohydrogen bondsbetween watermolecules
Evaporation from the leaves
SEM
Flow
of w
ater
• Cohesion• Adhesion
– Heat and temperature– 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.
Properties of Water
*solution
*solvent *solute *aqueous solution
Water is the solvent of life
The Chemical Basis of Life
Hydrophilic and hydrophobic substances*hydrophilic *hydrophobic
The dissociation of water molecules
H2O H+ + OH-
Acids and bases*acid
*base
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
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Incr
easi
ngly
aci
dic
gre
ater
H c
once
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Incr
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bas
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H c
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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
*structural isomers
*geometric isomers
*enantiomers
Example of enantiomers:
Chemical Components of Cells