ES 106 2006, April 10 Chemistry I. 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. ½% by volume 4. Iron—5% wt, 2 % #, ½% 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% #, ¼% 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+ + 2e- 2. Br + e- -->Br- 3. 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—worksV. 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-, deca- B. 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 proceedVII. 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
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