Announcements To join clicker to class today: – Turn on the Clicker (the red LED comes on). – Push “Join” button followed by “20” followed by the “Send” button (switches to flashing green LED if successful). % yield limiting reactants % composition – empirical vs. molecular formulas. ● Exam next Wed. ● Do not enter room until let in. ● Bring ID and Calculator. ● Quiz today sections Review

% Composition Molecules called ethylene and propylene are both % by mass H. The rest is carbon (85.628%). –M (ethylene)= g/mol –M (propylene)= g/mol Assume have 100 g of sample: – g H/in sample ( g H/mol H) = mol H/in sample – g C/in sample ( g C/mol C)= mol C/in sample – n H /n C = ( mol H)/( mol C) = – 2 H/ C or CH 2.

% Composition Calculate formula mass – (1 mole C/formula)( g C/mole C) + (2 mole H/formula)( g H/mole H) = g/formula Calculate number of times formula mass goes into molecular formula – MM(ethylene) = g/mole – / = 2 – molecular formula = C 12 H 22 = C 2 H 4

Chapter 3- Atomic Structure (light interaction with e - ) Historical perspective – Atom as (+) sphere with (-) electrons embeded – Rutherford Experiment suggested dense nucleus because alpha particles scattered – Evidence of Quantization from light: Photoelectric effect (E = h  ) so electrons not ejected until E photon > binding energy/work function. Extra energy ends up as kinetic: E photon =  + K.E. Line spectra of atoms. – Bohr Model of atom (orbiting electrons in specific orbits—problem is should fall in) – Wave Particle Duality (Debroglie relation:  =h/{mv}) explains as the electrons are standing waves around nucleus.

Chapter 3 con't Modern model of atom – Pauli exlusion principle and electron spin implies 2 electrons per orbital – Fill from lowest energy up. n= 1, 2,... s before p. – There are details use periodic table to determine actual configuration and do not forget about half-full and full subshells having extra stability. – Understand how concepts of penetration and shielding explain relative energies of shells and subshells. Periodic trends and how they are related (atomic size, ionization energy, formation of ionic compounds)

Chapter 4- Composition of the Earth and an Introduction to RXNs Composition of Earth (denser elements, mostly Fe, O, Si, Mg) Composition of early atmosphere (oxides of H, O, N, S) Naming of Simple compounds (binary: ionic vs. molecular, polyatomic ions, and oxoacids, learn polyatomic ions) Calculating molar mass Balancing chemical equations (by inspection) Stoichiometry (Percent yield, Limiting reagents, Chemical analysis & % composition.) – After balancing chemical equations all of these calculations require doing the following series of conversion given aA + … ––> bB + …: –g A –(÷ M A )–> mol A –([ratio fr/RXN])–> mol B –(x M B )–> g B. –For limiting reactants we do this process up to the moles of B stage for all reactants and only do the last step for the smallest moles of B.