ES 106 Spring 2007 Week 2 April 9 13 Water Properties Covalent bonds A Covalent bonds share electrons 1 Cl Cl Cl2 2 octet rule have eight electrons surrounding each element a may lead to need for multiple bonds for some atom pairs b stronger than single shared pair bonds 3 Naming covalent compounds a Use prefixes for each element determined by how many b Mono di tri tetra penta hexa hepta octa nona decaB Polarity of covalent bonds 1 identical nonmetals share electrons equally non polar dipole 2 different nonmetals a one element holds electrons more closely b polar molecule 3 electronegativity a fundamental property of elements b those further to right are more electronegative c those further to right dominate the shared electrons II Poly atomic molecules A Form several covalent bonds predicted by the formula 8 group number 1 draw the most electrically negative in the center of diagram 2 draw dot structure around it determined by its group 3 put atoms it bonds with around it where there are missing dots B poly atomic ions 1 made of several covalent bonds 2 charge does not cancel to zero so lacking octet of electrons 3 involved in ionic bonding as a coherent group not broken up C formulas of poly atomic molecules 1 subscripts attached to element only apply to that element 2 parentheses indicate poly atomic ion a subscripts attached to parentheses apply to all atoms in the group b be sure to multiply element subscript by group subscript 3 coefficients in reaction formulas tell how many of that molecule are needed for reaction to proceed III Shapes of molecules A Depends upon how octet of electrons is obtained B Draw electron dot structure showing bonds and unbonded pairs 1 count how many sets of bonds plus unbonded pairs 2 multiple bond is a single set C Shapes 1 linear two sets of bonds 2 triangular three sets 3 tetrahedral four sets 4 bent pyramidal created with unbonded pairs a count in initial shape b erased out and only actual bonds considered c H2O H2S SCl2 SO2 O3 I D Properties of substances depend upon shape and polarity of molecules 1 melting temperature 2 temperature of vaporization 3 bonding with other substances a hydrogen bonds where hydrogen is bonded to small atoms with large electronegativity b hydrogen exhibits stronger attractive forces than would be expected by the strength of its dipole 4 fluid substances with same type of bonds are soluble to one another a oil to gasoline b alcohol to water IV Water A Bent molecule B Covalent bonds C Has polarity acts as a dipole 1 oxygen end is negative 2 hydrogen end is positive D dissolves ionic substances because dipole is favorable to the bond with its ionic mate E Unusual properties 1 Depend on the polar nature of water molecule and hydrogen bonding 2 Solid state less dense than liquid state 3 High specific heat or heat capacity 4 High heat of vaporization 5 Readily dissolves ionic substances F Distribution 1 Covers 71 of Earth s surface 2 97 of water is salt sea water 3 2 of water is ice cap 4 Less than 1 remains as fresh surface water V Water cycle A evaporates 1 84 from sea surface 2 Evapotranspiration is a transpiration is plants releasing moisture to atmosphere b Evapotranspiration is combined effect 3 Becomes atmospheric moisture moved by winds B condensation into clouds allows precipitation 1 75 over sea 25 over land 2 Concentrated in tropical and midlatitudes 3 Much falls as snowfall a storage of solid water on land surfaces b Glaciers hold over 2 of Earth s water 1 Most of fresh water on land 2 If it melted sea level would rise 75 meters C runoff infiltration 1 back to the sea about 1 3 of land precipitation runs off 2 most of the other 2 3 of land precipitation is returned to atmosphere by evapotranspiration 3 groundwater storage removes water from cycle for long times VI Natural water composition A Rainwater contains impurities 1 dust from natural and man made sources 2 gases dissolved from atmosphere a nitrogen b oxygen c carbon dioxide d nitric acid B runoff and groundwater contain dissolved mineral material 1 Cations 2 Anions a sodium a bicarbonate b potassium b chloride c calcium 3 Silt etc d magnesium 4 Radon e iron 5 hard water contains ionic compounds of calcium magnesium and iron C Water contamination 1 micro organisms typhoid cholera dysentery 2 sewage adds organic material bacterial decay depletes dissolved oxygen killing fish a aerobic decay uses oxygen present b anaerobic decay after all oxygen used up 1 methane 2 sulfur hydrogen sulfide 3 fertilizers add plant nutrients lead to additional organic material to decay 3 industrial pollutants a Fertilizers and detergents 1 Nitrates replace oxygen on hemoglobin blue baby syndrome 2 Algal bloom increases BOD b petroleum and its derivatives 1 gasoline diesel leak from 10 of underground tanks 2 volatile organic compounds a solvents cleaners carcinogenic b persistent because of lack of reactivity c benzene toluene carbon tetrachloride c acids directly and acid rain 1 acid mine drainage from sulfur compounds in ore minerals 2 air pollutants cause rainwater to become acidic a sulfur from eastern coals burned in power plants b nitrogen from auto and industrial emissions 3 neutralized naturally by limestone not by granite d radio isotopes pesticides toxic metal chemicals 1 water requirement to produce steel paper plastic 2 cleaning water to be released to streams major expense 4 measured in parts per million and parts per billion a some are dangerous at minute levels b some are over sensationalized in media presentation Heat and Energy VII Heat A Moves from substance that has more into substance that has less 1 heat is the motion of the energy from one substance to the other 2 molecules have energy of motion not heat 3 Cold is not a quantity it is the absence of heat a Temperature related to the random molecular motion of the substance b Heat transferred from substance with higher temperature to one with lower temperature c As heat is transferred molecular energy changes 1 May not change temperature if a phase change is occurring 2 Reflected in a change in temperature of the substance B Heat is measured in joules or calories 1 one calorie 4 184 joules 2 one Calorie in food is 1000 calories really one kilocalorie VIII Specific Heat Capacity A Quantity of heat to raise quantity of substance 1o C B calorie heat to raise 1 gram water 1o C C water has a very large specific heat capacity 1 results in water moderating temperature 2 maritime areas more mild in
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