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CHAPTER 2Life’s Chemical Basis
THE BASICS Matter—anything that has mass and
takes up spaceSolidLiquidGas
THE BASICS Element—unit of matter than cannot be
broken down further by ordinary chemical reactions92 naturally occurring elements98% of weight of any living thing is made
up of 6 Carbon Hydrogen Oxygen Nitrogen Phosphorous Sulfur
BUILDING BLOCKS Atom—smallest indivisible unit of an
element Molecule—multiple atoms of the same
element bonded together Compound—multiple atoms of different
elements bonded together
ATOMS Three subatomic particles
ProtonsNeutronsElectrons
BOHR MODEL
BOHR MODEL
BOHR MODEL
ELECTRON ORBITS Orbit in “shells” K Shell—2 electrons L Shell—8 electrons M Shell—18 electrons
PERIODIC CHART Atomic Number=Protons Atomic Mass=Protons + Neutrons
PERIODIC CHART Elements in their natural state have
neutral chargePositive charge (protons) equals negative
charge (electrons)
ISOTOPES Change in the number of neutrons Does not affect charge Carbon-14
Atomic Mass = 14 (6 Protons + 8 Neutrons) Radioisotopes in medical diagnosis
IONS Change in the number of electrons Affects charge
Anion—negative chargeMore electrons than protons
Cation—positive chargeMore protons than electrons
BONDS Ionic Covalent Hydrogen
INERT ELEMENTS
ACTIVE ELEMENTS
IONIC BONDS Formed between ions Electrons transfer from one atom to another Opposite charges attract and hold atoms Usually inorganic (acids, bases, salts, etc.)
COVALENT BONDS Atoms share electrons Happens when both have room Usually organic (proteins, carbohydrates, etc.)
COVALENT VS. IONIC
HYDROGEN BONDS Bond between covalently bonded
hydrogen atom & atom in different molecule or different location.
Individually weak, but collectively strong.
WATER Biologically important Makes up 70-90% of living things Unique properties
WATER Polar molecule (slight positive &
negative charge)Can easily dissolve other polar moleculesHydrophilicHydrophobic“universal solvent”Cell membranes
Temperature stabilizingKeeps cell processes from generating too
much heatEvaporation Ice helps insulate
WATER “Stick together”
Adhesion—water sticks to itselfCohesion—water sticks to other polar
moleculesDue to polarity & hydrogen bonds
ACIDITY pH scale
0-14Based on H+ & OH- moleculesGreater H+, lower the pHEach unit is 10-fold change
going from pH 6 to 5 increases H+ by 10 times
ACIDITY Acids
Donates H+
pH less than 7 Bases
Accepts H+
Releases OH-
pH greater than 7 Neutrals
Release equal numbers of H+ and OH-
pH 7.0
ACIDITY Buffers
Biological substances that help regulate pHRelease or absorb H+ to keep pH unchangedEx.—Carbonic Acid, Bicarbonate regulate
blood
H2CO3 + OH- HCO3- + H20
HCO3- + H+ H2CO3