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Chemistry Review
AP Biology
Chapter 2: The Chemical Context of Life
Matter, Elements, and Compounds• Matter
• Anything that takes up space or has mass
• Element• “Pure” substance that cannot be broken
down• 92 naturally occurring in nature
• Compound• Two or more elements combined in a fixed
ratio
Life’s chemical requirements
• 25 of 92 elements are required• Carbon, nitrogen, hydrogen and oxygen
make up 96% of living matter
• Trace elements• Required in minute quantities• Some needed by all life forms• Others only by certain species
Atomic StructureWhat are these called?
These have what charge?
These have what charge?
Reading the periodic table
Isotopes and Radioisotopes• Isotopes
• Different forms of element due to # of neutrons
• Radioisotopes• Nucleus decays
spontaneously• Date fossils• Used to trace atoms
through metabolisms• Can damage cellular
molecules
Electron configuration• Energy levels
• Closest shell = least energy
• Farthest shell = most energy
• Energy is gained/lost by moving shells
• Orbital• 3-D place where e- are
usually found• 2 e- per orbital
• Valence electrons and shell• Outermost e-• Complete outer shell =
non-reactive
Chemical Bonding
• Interactions between atoms• Covalent – shared e-
• Non-polar covalent• Polar covalent
• Ion – charged atom• Anion (-)• Cation (+)
• Ionic bond – “steals” e-
Weak chemical bonds• Hydrogen bonds
• Hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom
• Hydrogen bonds, ionic bonds and other weak bonds help form proteins
Reactants and Products
• Chemical reactions• Make and break chemical bonds, change composition of
matter• Reactants and products
• Starting and ending materials of chem rxns• Matter cannot be destroyed, but rearranged
• Most chemical rxns are reversible• Chemical equilibrium
• When reactions offset one another• Rxns still happening, but no effect on reactant/product
concentrations• Reactants and products are NOT equal in concentration
Chapter 3: Water and the Fitness of the Environment
Polarity and Hydrogen Bonding
• Polar molecule• Has opposite charges
at different ends
• Each water molecule can bond to a max of 4 others
Water Properties and Organisms• Water molecules stick together
due to hydrogen bonds• In liquid form, bonds are fragile• Each bond lasts one trillionth a
second
• Cohesion – bonds collectively hold substance together• How plants transport water• Hydrogen molecules tug on
molecules further down the vessel• http://faculty.pingry.org/thata/
pingry_upload/movies/water_macromolecules/cohesion_transport.mov
• Adhesion• Clinging of one
substance to another
• Surface tension• Measure of how
difficult it is to break the surface of a liquid
Water & Earth
• Moderates temperatures, contributing to habitability
• Kinetic energy• Energy of motion
• Heat• Measure of total kinetic energy due to
molecular motion
• Temperature• Intensity of heat due to avg. kinetic
energy
• Celsius scale
Water and Earth, cont.• Calorie
• Amount of heat energy needed to raise 1g of water by 1°C
• Kilocalorie• Amount of heat energy
needed to raise 1kg of water by 1°C
• Joule• = 0.239 calories (one
calorie = 4.184 J)
Water and Earth, cont.• Specific heat
• Amount of heat absorbed or lost for 1g of substance to change 1°C
• Specific heat of water is 10x that of iron
• Water resists change in temp
• High specific heat of water makes ocean temp stable for life
• Organisms made mostly of water resist temp changes
Water and Earth, cont.• Liquid molecules moving
fast to overcome bonds enter air as gas• Vaporization or
evaporation• Takes 580 calories of heat
to evaporate 1g of room temp water
• Evaporative cooling• As substance evaporates,
surface of remaining substance cools down
Ice Floats
• Why oceans and lakes don’t freeze
• Water is less dense as a solid than as a liquid• Expands when frozen• Reaches its greatest density at 4°C
• If ice sank, all ponds, lakes, and oceans would freeze solid
• How would this affect life?
Water is the solvent of life• Solution
• Solvent + solute
• Solvent• Does dissolving
• Solute• What dissolves
• Aqueous solution• Solution with water as solvent
• Water works well, but not for everything, otherwise could not be stored
Water is the solvent of life, cont.• Hydrophilic
• Has affinity for water• Hydrophobic
• Repels water• Mole
• Equal in # to molecular weight of substance in grams
• Molecular weight• Sum of all weights of all atoms in
a molecules• Avagadro’s number = 6.02 x 1023
(# molecules/mole)• Molarity
• Moles of solute per liter of solution
Organisms and pH• Organisms are sensitive to
pH
• Hydrogen ion• (H+) single proton with charge
of +1
• Hydroxide ion• (OH-) charge of -1
• Dissociation • Transfer of hydrogen atoms
pH• Acid
• Substance that increases H+ concentration of a solution
• Donate H+ to a solution• When hydrochloric acid is added to water HCl H+ +
Cl-
• Base• Substance that increases OH- of a solution
• Concentrations of H and OH• Products of OH- and H+ concentrations are always
10-14
pH, cont.• pH scale
• Range from 0-14, expresses OH- and H+ concentrations
• Defined as –log[H+]• pH declines as H+ concentration increases• Each pH unit represents 10-fold difference in
OH- and H+ concentrations
pH, cont.• Buffers
• Substances that minimize changes in pH• Accepts and donates ions in solution when
needed• Ex: carbonic acid
Acid Precipitation & Environment
• Threatens the fitness of environment
• Acid precipitation• Rain, snow, or fog more acidic than pH 5.6
• Harms environment by killing plants and animals
Chapter 4: Carbon and the Molecular Diversity of Life
Carbon• Prominent role in evolution of life
• Can form molecules that are large, complex, and diverse
• Complexity is demonstrated in hemoglobin
Organic Chemistry• Study of carbon compounds
• 30% of a cell is carbon based compounds
• Common ingredients in carbon compounds: H, O, N, S, P
Carbon atoms are a versatile building block
• Carbon has 6 electrons• Little tendency to gain or lose
e- and form ionic bonds• Completes valence shell by
making 4 covalent bonds• Makes large, complex
molecules possible• Carbon is compatible with
many different elements• CO2 is the source of carbon for
all the organic molecules found in organisms
Variation = Diversity• Variation in carbon
skeletons contributes to the diversity of organic molecules
• Carbon chains form the skeletons of organic molecules
• Hydrocarbons• Organic molecules
consisting only of carbon and hydrogen
Variation = Diversity, cont.
• Isomers• Compounds with same
molecular formula, but different structures, hence different properties
• Structural isomers• Differ in the covalent
arrangements of their atoms
Variation = Diversity, cont.
• Geometric isomers• All have same
covalent partnerships, differ in their spatial arrangements
• Stereoisomers• Molecules are mirror
images of each other
Functional Groups• Contribute to the molecular diversity of
life• Hydroxyl group
• H atom bonded to a O atom, in turn bonded to the C skeleton
• Alcohol: organic compounds containing hydroxyl groups
• Polar because of electronegative oxygen
• Carboxyl• O double bonded to a C, bonded to
hydroxyl
Functional Groups, cont.
• Amino• N bonded to 2 H atoms
• Sulfhydral• S bonded to H
• Phosphate• P ion convalently attached by O atom to C
skeleton
Chemical Elements of Life: Review
• Living matter consists of mainly C, H, O
• Chemical behavior of carbon makes it a versatile building block