ES 106 I 2006 April 10 Chemistry Elements in Earth s crust A Most common eight 1 Oxygen a 47 by weight b 63 by number of atoms c 94 by volume 2 Silicon a 28 by weight b 21 by number of atoms c 1 by volume 3 Aluminum a 8 by weight b 6 by number of atoms c by volume 4 Iron 5 wt 2 by volume 5 Calcium 4 wt 2 1 by volume 6 Sodium 3 wt 3 1 by volume 7 Potassium 3 wt 1 2 by volume 8 Magnesium 2 wt 2 by volume B Minerals are composed of bonded elements 1 naturally occurring inorganic solid with an orderly internal arrangement of atoms crystalline structure and a definite chemical composition that can vary within limits 2 most minerals in Earth s crust are silicates a compounds containing oxygen and silicon b building block is the silica tetrahedron one oxygen four silicon II Electron dot diagrams are useful for predicting bonding of elements dots surrounding the element represent its valence electrons A Show how elements bond by filling or emptying dot shell B become ions with dots charges and electrons 1 Ca Ca2 2e2 Br e Br3 Show ionic bonding reactions by transfer of electrons only III Naming Compounds A Cations take on their element name plus ion B Anions names derive from their element name 1 change ending to ide 2 plus ion C put two names together cation first anion after IV formulas of ionic compounds A find charges of ions from location in periodic table B combine so charges cancel to zero electrically neutral compound C book states to crossover the charge amounts into subscripts works V 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 VI 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 VII 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 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 VIII 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
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