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Biology: September 12th, 2013: Chapter 2
Chemical basis of life: atoms, molecules, & water
Atoms Chemical Bonds Properties of water
Electrons
Have potential energy due to their position relative to the
nucleus Farther away from nucleus = more energy
Elements
Cannot be broken down into other substances 4 of the essential
elements make up about 96% of living mater
o CARBON, NITROGEN, OXYGEN, and HYDROGEN Other 4% are:
o PHOSPHOROUS, SULFUR, & CALCIUM Other 17 elements are trace
elements
o Iron, IodineMolecule
2 or more atoms bonded togetherCompound
Molecule composed of 2 or more elementsTypes of bonds
Covalent- strongesto Polaro Non-polar
Hydrogen Ionic
Electronegativity
The attraction of an atom for electrons The more
electronegative, the more that atom pulls the electrons
towards itself
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Covalent Bond
Atoms share a pair of electrons Occurs between atoms whose outer
electron shells are not full Strongest bond Non-polar if the share
the electrons equally
Non-polar Covalent Bonds
Between atoms with similar electronegativities Equal sharing of
electrons No charge difference across molecule
Polar Covalent Bonds
Not equal sharing of electrons One atom is MORE electronegative
that the other(s)
Hydrogen Bonds
Very important for life Weak alone, but additive when
combined
Ionic Bond
One atom is much more electronegative than the otherIons
Cationo Positively charged
Aniono Negatively charged
Ionic bond occur when a cation bonds with an anionChemical
Reactions
Occurs when one or more substances are changed into
othersubstances
o Reactants products Share many properties
o All require a source of energy
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o Reactions in living organisms often require a
catalyst(enzymes)
o Tend to proceed in a particular direction but will
eventuallyreach equilibrium
o Occur in liquid environment - water Make and break chemical
bonds
Properties of water
Solutiono Solvent-liquido Solutes-substances dissolved in
solvent
Aqueous solutiono Water is the solvent
Ions and molecules that contain polar covalent bonds will
dissolve nwater
Hydrophilic
water-lovingHydrophobic
water-fearingAmphipathic molecule
Both polar and non-polar regions of the molecule May form
micelles in water
Solutions
Concentrationo Amount of a solute dissolved in a unit volume of
solutiono 1 gram of NaCl was dissolved in 1 liter of water =
1g/L
Molecular weight and moles
Mw =o Atomic mass of all atoms x the number there are of each
one
Sucrose = C12H22O11 = (12 x12) + (22 X1) + (11 x16)= 342 D
(Daltons)
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1 mole = The molecular weight of a compound in gramso 1 mole of
sucrose = 342 gramso one mole of anything contains the same number
of molecules
different weights, but same number of molecules 6.0234e23
molecules = 1 mole
Molarity
Concentration amount Solute/Solvent Moles/Liter = Molar solution
= M
Water
Extremely stable as a liquido Hydrogen bonds
Depend ono concentration of dissolved solute particles ando not
on the specific type of particle
Addition of solutes to watero Decreases freezing pointo
Increases boiling point
Some animals produce antifreeze molecules that dissolve in
theirbody fluids
o Can live in cold environments or withstand
freezingtemperatures
Participates in chemical reactionso Hydrolysis or
dehydration
Provides force or support Removes toxic waste components
Evaporative cooling Cohesion and adhesion
Properties of water due to hydrogen bonding
Cohesiono Water molecules stick together
Capillary transport Adhesion
o Water molecule stick to surfaces
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Capillary transport Surface tension
Heat of Vaporization
Amount of heat needed for 1 gram of a substance to vaporizeWater
is the Solvent of Life
It will dissolve the most popular molecules, even most
proteins,DNA, RNA, and sugar
o Unless they are too big EX) cellulose
It will dissolve molecules that have ionic bonds - example salt!
Will not dissolve hydrophobic molecules
Dissociation of Water molecules
Sometimes a Hydrogen atom participating in a H-bond between
2water molecules will go off with the wrong water molecule
It leaves behind its electron What actually gets transferred is
the hydrogen ion - a single proton This results in 2 ions being
formed
o A Hydroxyl ion and A Hydronium ion
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9/12/2013 5:12:00 AM
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9/12/2013 5:12:00 AM
