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Chemistry Class Announcements and Review

Join the class by clicking the Clicker and following instructions. Exam and Quiz details provided. Review of % Composition and Atomic Structure. Learn about Chapter 4 topics. Periodic trends and stoichiometry overview included.

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Chemistry Class Announcements and Review

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  1. 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). • Exam next Wed. • Do not enter room until let in. • Bring ID and Calculator. • Quiz today sections 4.2-4.8. • % yield • limiting reactants • % composition • empirical vs. molecular formulas. Review

  2. % Composition • Molecules called ethylene and propylene are both 14.372% by mass H. The rest is carbon (85.628%). • M(ethylene)= 28.054 g/mol • M(propylene)= 42.081 g/mol • Assume have 100 g of sample: • 14.372 g H/in sample (1.0079 g H/mol H) = 14.259 mol H/in sample • 85.628g C/in sample (12.011 g C/mol C)=7.1291 mol C/in sample • nH/nC = (14.372 mol H)/(7.1291 mol C) = 2.0000 • 2 H/ C or CH2.

  3. % Composition • Calculate formula mass • (1 mole C/formula)(12.011 g C/mole C) + (2 mole H/formula)(1.00794 g H/mole H) = 14.027 g/formula • Calculate number of times formula mass goes into molecular formula • MM(ethylene) = 28.054 g/mole • 28.054/14.027 = 2 • molecular formula = C1•2H2•2 = C2H4

  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 = hυ) so electrons not ejected until Ephoton > binding energy/work function. Extra energy ends up as kinetic: Ephoton = φ + 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: λ=h/{mv}) explains as the electrons are standing waves around nucleus.

  5. 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)

  6. 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 –(÷MA)–> mol A –([ratio fr/RXN])–> mol B –(xMB)–> 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.

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