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THE CHEMICAL CONTEXT OF LIFE
Campbell and ReeceChapter 2
ELEMENTS & COMPOUNDS
Element: substance that cannot be broken down to other substances by chemical reactions
92 natural-occurring elements
COMPOUNDS
2 or more different elements combined in a fixed proportion
compound has different properties than properties of individual elements that make up the compound
WHICH OF THESE ARE COMPOUNDS?
ESSENTIAL ELEMENTS OF LIFE
those of the 92 that organisms must have to live & reproduce
species specific; humans need 25 elements plants need 17
ESSENTIAL ELEMENTS
96% of living matter (by mass) made up of:
Oxygen Carbon Hydrogen Nitrogen
4% of living matter (by mass) made up of:
Calcium Phosphorus Potassium Sulfur Chlorine Magnesium
Trace Elements make up <1% organisms require these in minute
amounts to name only a few: Iron Iodine (in vertebrates only) Zinc Selenium Manganese
TOXIC ELEMENTS
Arsenic Mercury
PROPERTIES OF ELEMENTS
ATOMIC MASS
1 proton or 1 neutron = 1 amu 1 amu = 1.7 x 10² g = 1 dalton mass of e- ignored
MASS NUMBER
#protons + #neutrons
ISOTOPES
different forms of same element: same # protons different # of neutronsoccurs naturallyAtomic Mass see on periodic table is
weighted mass average of all isotopes
RADIOACTIVE ISOTOPES
nucleus spontaneously decays giving off particles & energy used medically to measure an
organ’s function, monitor tumor growth
RADIOACTIVE ISOTOPES
decay hazardous to living organisms by damaging cellular molecules
ENERGY LEVELS OF ELECTRONS
electrons only subatomic particle involved in chemical reactions
e- have PE due to their position around nucleus of atom
electron’s (-) charge attracted to (+) proton
the farther out e- is from nucleus, the more PE that e- has
ELECTRON ENERGY LEVELS
VALENCE ELECTRONS
electrons in outermost shell if valence shell completely filled:
atom is nonreactive (inert like noble gases)
ELECTRON ORBITALS
CHEMICAL BONDS
formed by interactions between atoms with incomplete valence orbitals
COVALENT BONDS
sharing of a pair of valence electrons by 2 atoms
2 or more atoms held together by covalent bonds = molecule
TYPES OF COVALENT BONDS
1 pair e- shared = single covalent bond
2 pair e- shared = double covalent bond
3 pair e- shared = triple covalent bond
hydrogen gas
NONPOLAR COVALENT BOND
shared pair of electron are shared evenly between the 2 atoms
ELECTRONEGATIVITY
attraction of a particular atom for the electrons in covalent bond
greater the electronegativity on 1 atom over the other in the covalent bond, the more likely the bond will be a polar covalent bond
POLAR COVALENT BONDS
electrons of the bond are not shared equally
bonds vary in their polarity: depends on the relative electronegativity of the 2 atoms
IONIC BONDS
transfer of e- from metal nonmetal
creates cations (+) & anions (-) opposite charges attract forming
ionic bond compounds formed by ionic bonds
called ionic compounds or salts as solids form crystals, very strong
bonds as liquids completely dissociate
WEAK CHEMICAL BONDS
in living organisms: most of the strongest chemical bonds are covalent
weak bonds also important: hydrogen bonds, van der Waals, ionic
bonds in water maintain shape of proteins, DNA reversibility key to their importance
HYDROGEN BONDS
water: H held to O in polar covalent bonds
partial (+) charge on H makes it attract the partial (-) charge on O from another water molecule
VAN DER WAALS FORCES
nonpolar covalent bonds may not have electrons symmetrically distributed
@ any given instant in time a region of the molecule may be slightly (-) or (+) ever-changing regions of (+) or (-) charge
occurs only when atoms or molecules are very close together
MOLECULAR SHAPE & FUNCTION
shape of a molecule key to its function in cell
shape of a molecule with >2 atoms determined by positions of atom’s orbitals
MOLECULAR SHAPE
determines how biological molecules recognize & respond to each other with specificity
2 molecules temporarily forming weak bond can only happen if their shapes are complimentary to each other
MOLECULAR SHAPE
because morphine and endorphins have same shape that fits into endorphin receptors morphine is able to create same response as endorphins: pain relief & euphoria during stress
ENDORPHINS & MORPHINE
CHEMICAL REACTIONS
chemical bonds of reactants broken, chemical bonds of products formed in a chemical reaction
CHEMICAL EQUILIBRIUM