The Chemical Basis of Life

Matter—anything that has mass and takes up spaceSolidLiquidGas

Element—unit of matter than cannot be broken down further by ordinary chemical reactions92 naturally occurring elements96% of weight of any living thing is made

up of 4 Carbon Hydrogen Oxygen Nitrogen

Atom—smallest indivisible unit of an element

Molecule—multiple atoms of the same element bonded together

Compound—multiple atoms of different elements bonded togetherNa (sodium) + Cl (chlorine) = NaCl (sodium

chlorideNa is a metalCl is a poisonous gasNaCl is table salt

Three subatomic particles

NucleusProtons & NeutronsCenter of atom

OrbitsElectronsSurround nucleus like

planets around a sun

Particle Charge Mass Location

Protons +1 1 Nucleus

Neutrons 0 1 Nucleus

Electrons -1 0 Orbit

Orbit in “shells”Valence shell—

outermost orbit Octet Rule

Atoms form bonds to have 8 electrons in the valence shell

Atom either gains, loses, or shares electrons to adhere to octet rule

Atomic Number=Protons Atomic Mass=Protons + Neutrons

Number of electrons = number of protons In a stable atom in a natural state

Elements in their natural state have neutral chargePositive charge (protons) equals negative

charge (electrons)

Example—Nitrogen Number of Protons?

7 (atomic number) Number of Neutrons?

Atomic mass is 14 Atomic mass is Protons + Neutrons If protons are 7, put into formula…7+X=14…and

solve for X Or…Atomic Mass minus Atomic Number =

Neutrons 7

Number of Electrons? 7 (same as Protons)

Change in the number of neutrons Does not affect charge Does not affect base element Isotopes are often unstable Carbon-12 (12C)

Basic elemental carbon Carbon-14 (14C)

Atomic Mass = 14 (6 Protons + 8 Neutrons)Used in dating ancient materials

Radioisotopes in medical diagnosis

Change in the number of electrons Affects electrical charge

Anion—negative chargeMore electrons than protonsCl- (17 protons, 18 electrons)

Cation—positive chargeMore protons than electronsNa+ (11 protons, 10 electrons)

Union between atoms Positive (protons) and negative

(electrons) charges attract each other Similar charges repel (electrons &

electrons)

Atoms will not bond with other elements Valence shell already filled Non-reactive

Will bond with other elements

Valence shell not full

Reactive

Formed between ions Electrons transfer from one atom to another Opposite charges attract and hold atoms

Na+ + Cl- = NaCl Usually inorganic (acids, bases, salts, etc.) Weak bonds

Dissolve in water

Atoms share electrons Happens when both have room Stronger than ionic bonds Usually organic (proteins,

carbohydrates, etc.) Nonpolar bond

Share electrons equally

Polar bondAtoms share electrons unevenlyElectron spends more time around one atom than

anotherSince electrons have a negative charge, one end

(“pole”) has a slight negative charge, and one pole is slightly positive

Bond between hydrogen atom of one polar compound and a different atom of another polar compound Positive charge on H attracted to negative

charge on other compound Individually weak, but collectively strong. Important to many biological compounds

Biologically important Makes up 70-90% of living things Unique properties

Determined by hydrogen bonds

Polar molecule (slight positive & negative charge)Hydrophilic— “Water loving”

Polar compoundsHydrophobic— “Water hating”

Nonpolar compounds

Temperature stabilizingLarge amounts of energy required to change

temperatureKeeps cell processes from generating too much

heatEvaporation Ice helps insulate

“Stick together”Cohesion—water sticks to itselfAdhesion—water sticks to other polar

moleculesDue to polarity & hydrogen bonds

“Universal solvent”Dissolves saltsDissolves other polar compounds

pH scale0-14Based on H+ concentrationGreater H+, lower the pHEach unit is 10-fold change (logarithmic)

going from pH 6 to 5 increases H+ by 10 times

AcidspH less than 7Release H+ into

solution Bases

pH greater than 7Release OH- into

solutionAccepts H+ from

solution Neutrals

pH 7.0

BuffersBiological substances that help regulate pHRelease or absorb H+ to keep pH unchangedResists pH changes

SaltsFormed when acids & bases combineNaOH + HCl = NaCl + H20