The Chemical Basis of Life

 Matter—anything that has mass and takes up space  Solid  Liquid  Gas

 Element—unit of matter than cannot be broken down further by ordinary chemical reactions  92 naturally occurring elements  96% 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 together  Na (sodium) + Cl (chlorine) = NaCl (sodium chloride  Na is a metal  Cl is a poisonous gas  NaCl is table salt

 Three subatomic particles  Nucleus  Protons & Neutrons  Center of atom  Orbits  Electrons  Surround nucleus like planets around a sun ParticleChargeMassLocation Protons+11Nucleus Neutrons01Nucleus Electrons0Orbit

 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 charge  Positive 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 ( 12 C)  Basic elemental carbon  Carbon-14 ( 14 C)  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 charge  More electrons than protons  Cl - (17 protons, 18 electrons)  Cation—positive charge  More protons than electrons  Na + (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 bond  Atoms share electrons unevenly  Electron spends more time around one atom than another  Since 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 compounds  Hydrophobic— “Water hating” Nonpolar compounds  Temperature stabilizing  Large amounts of energy required to change temperature  Keeps cell processes from generating too much heat  Evaporation  Ice helps insulate

 “Stick together”  Cohesion—water sticks to itself  Adhesion—water sticks to other polar molecules  Due to polarity & hydrogen bonds  “Universal solvent”  Dissolves salts  Dissolves other polar compounds

 pH scale  0-14  Based on H + concentration  Greater H +, lower the pH  Each unit is 10-fold change (logarithmic) going from pH 6 to 5 increases H + by 10 times

 Acids  pH less than 7  Release H + into solution  Bases  pH greater than 7  Release OH - into solution  Accepts H + from solution  Neutrals  pH 7.0

 Buffers  Biological substances that help regulate pH  Release or absorb H + to keep pH unchanged  Resists pH changes  Salts  Formed when acids & bases combine  NaOH + HCl = NaCl + H 2 0