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