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