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## What to expect when you’re expecting…

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**…A Gen Chem. Final…**Problems will look like those you’ve already faced. Hints for studying? Read the Chapter summaries…note the MAIN ideas from each. Exam will cover both ‘theory’ and problem solving. Develop your chemistry vocabulary (terms/definitions help) Look at common problem types (we’ll get to these as well). What to expect when you’re expecting…**More of the Foundation**• molarity/dilution calcuations (yes, you’ll see this) • balancing chem. equation—basic. • STOICHIOMETRY, gmolmolg must know this • In fact, you need the BCE to develop the most BASIC conversion—the mole to mole conversion!! • Limiting reactant, theoretical yield, actual, % • Yes, you will see another problem like this…a MUST know!! • And of course, the ‘what you should know’ from 1st week • Given in the handout**Where to begin? With the atom…**• All of these concepts were built upon the ideas from physicists regarding structure of the atom • Rutherford—nucleus, dense central core • Planck—atomic orbitals are quantized…discrete E levels • Schroedinger—gave equation for 3-D position of electrons • This yielded quantum numbers… • Quantum numbers describe the energy level of an electron (n), the shape of the orbital (l…the lower case L), the number of ortibals (ml) and the spin (ms = +/- ½)**Quantum #’s are used to establish energy levels for**electrons in a free atom. • Energy levels lead to electron configurations • Electron config’s indicate valence/core e-’s • Electron configurations help to predict periodic trends/properties • Atomic radius, ionic radius, ionization energy • And…oh yes, you should know these trends… • Atoms bind to form molecules…chemical bonds.**Concepts for molecular shape**• This chapter extends the Lewis dot notation (valence electrons) from Chapter 7 • Learned the following (note how it builds) • # valence electrons in an atom • # covalent bonds an atom forms • Resonance/Formal Charge • The Octet Rule • Drawing Lewis structures (takes practice) • Electron Geometry (how ALL e pairs fit) • Molecular Geometry (ONLY bonding e’s) • Exam questions will look like that—given a molecular formula, draw the Lewis structure (assign formal charge, resonance) and describe the geometry**Determine the number of valence electrons**• Draw a skeletal structure (takes practice…use table below) • Distribute excess electrons—make octet • Excess electrons go to central atom, deficiency—multiple • Calculate formal charge of each atom (table below helps)**Valence Shell Electron Pair Reupulsion**• Fancy way of saying electrons repel each other. • VSEPR predicts shape based on maximizing distance • Number of Electron Groups dictates the shape a molecule adopts • 2 Electron Groups—linear • 3 Electron Groups—Trigonal planar • 4 EG’s (tetrahedral) • 5 EG’s trigonal bipyramidal • 6 OH (octahedral)**Helps to define electron group**EG’s are ANY group of electrons, bonding, lone etc. Single bond Double bond Triple bond Lone pair of electrons Radical (one e) Remember, it maximizes the repulsion between ALL electrons EGG’s ARE important though… HOWEVER, we more often care about the shape of the MOLECULE; bonding pairs only (lone/radicals be damned) Molecular Group Geometry describes the orientation of JUST the bonding pairs More accurately stated…the bonding GROUPS Maddeningly enough, some molecules have LONE pairs, so what to do? Electron Groups “defined”**Shapes of simple structures**• Two and Three EG’s: • Little variation in the shape • Two is always linear • Three has two options • Bent, or trigonal planar**4-Coordinate…Organic**• Not really going to drag this out much, you ALL should know this pretty well • Methane, ammonia and water, the unholy trinity? • 4:0 tetrahedral • 3:1 trigonal pyramidal! • 2:2 bent (or ‘angular’) • Note bond angles!!**Formal Charge—Quick and Dirty**• Books give a formula for calculating formal charge, but those are pretty clunky…something simpler • Count all bonds (as 1) and lone pair electrons (1 for each electron) • Btw…thiocyanate? Replace the O with an S O C N # valence e’s (for element) 6 4 5 Number e’s (see counting) 6 4 6 Subtract 2 from 1 0 0 -1 Formal Charge resides on Nitrogen Here, formal charge is on the oxygen. Are these resonance forms?**Cartoon of the conversions…**• The cartoon below gives the ‘roadmap’ btw concepts, but what are the names of these roads? MOLARITY MOLARITY Gram Gram MOLE MOLE Heat PV = nRT PV = nRT**Chapter 3 ‘problem types’**• Chapter 3 introduces many ‘problem types’. • BCE’s • Stoichiometry (simple gram to mole conversions) • Limiting reagent (application of above) • Yields (theoretical/actual/%)—from limiting reagent • Molarity (very important for titration calcs) • %composition/empirical/molecular formula**Problems from the ‘physics’ of chemistry**• Quantum Mechanics (chapter 5) gives us several simple relationships that govern the behavior of atoms. • All EM radiation can be described using frequency (n) and wavelength (l)—and interacts with matter • Wavelength—distance between crests of a wave (lambda) • Frequency—number of crests per unit time, n (measured in sec) • nl = c or n = c / l • c is the speed of light (2.998 x 108 m/s) • Let’s relate the above to something useful, like energy. E = hc/l • h? It’s Planck’s constant,6.626 x 10-34J·s**Chapters 6/7—energy (rxns etc)**• Chapter six gives us energy—new chemical compounds aren’t the only thing produced in a chemical reaction, heat is too (TREATED THE SAME AS g—m—m—g! • Energy also introduces new terms like system and surroundings…exo- and endothermic • Exo-endo-thermic and signs, know these • Specific heat capacity • Two ‘equation types’… • q = m c ΔT and • ΔH, ΔS, ΔG, • ΔG = ΔH - T ΔS**Ideal Gas Law**• The IGL—quite possibly the easiest chapter (in terms of problems) this term. • Can you remember one simple equation? If so, then Chapter 9 will be ridiculously simple • PV = nRT • Five types of problems come from that equation • Plug and chug partial pressure • Density molecular mass • Change in one variable • Pressure/Temp conversions (mmHg, Torr—760 = 1 atm) • Must calculate all IGL problems in Kelvin (°C + 273.15)**End of the informal “review”**• I have ~ 30-ish problems from the end of each chapter; ‘Multi-Concept’ problems that require you to have a firm foundation in most of the material I’ve presented. • NOT COMPREHENSIVE!! A good first step! • I will post these on my website later tonight/tomorrow • Posted answers? Stop by if you’re stuck, I may post the answers not given in the back of your book. • Your turn…