Holiday Magic Demo Show. Wednesday, December 12 th, 7:00pm Sunday, December 16 th, 2:00pm (located in 100 Noyes Lab)

Transcription

1 Holiday Magic Demo Show Wednesday, December 12 th, 7:00pm Sunday, December 16 th, 2:00pm (located in 100 Noyes Lab)

2 Announcements 1. Exam 3 grades are posted on-line. 2. Get exams back in lab tomorrow. 3. ICES Online Evaluations 4. Finals Office hours 1. TA office hours will be posted online today 2. My office will be open for appointments from 9am-5pm all this week and next week 3. Also anytime my Doctor Is In sign is up feel free to stop by

3 TA Finals Office Hours Puzhou Wang: Friday 12/14, 12-4pm in CLC Alex Stanton: Friday 12/14, 1-3pm and Tuesday 12/18, 1-3pm Anna Wetherholt: Friday 12/14, 3-5pm in CLC Liz Ohr: Sunday 12/16, 4-6pm in Noyes 331/333 Derek Le: Monday 12/17, 12-3pm in Noyes 331/333 Lauren Cunningham: Monday 12/17, 12-3pm in Noyes 331/333 Zack Gordon: Monday 12/17, 1-3pm in CLSLA404 Doug Rybar: Tuesday 12/18, 4:30-6:30pm in CLC (also by appt) Nitin Neelakantan: by appointment

4 Exam III Grades Raw exam scores: High score: 60/60 Average score: 42.3/60 Low score: 11/60 Scaled exam scores: High score: 100/100 Average score: 77.6/100 Low score: 26/100

5 Final Exam Wednesday, Dec. 19 th, 8:00-11:00am 50 multiple choice (No free response!) Worth 300 points (30% of final grade) Cumulative Exam locations will be posted online today Bring calculator and extra pencils Safety during finals week!

6 Final Exam Tips BE CAREFUL OF ERASER MARKS! Mark answers in booklet first, then once you have finished the exam go back and fill in the scantron Do what you know! If you can t remember how to do a problem after thinking about it for 1 minute, just skip it! The time you waste trying to remember how to do one problem could be used to answer other problems! Each problem is worth 6 points, so concentrate on just answering as many as you can For the ones you don t know, make an educated guess!

7 Final Exam Study Tips As you review, check that you actually comprehend a topic Close the book/notes and try to recall the concepts without looking Get in study groups and quiz each other on the concepts Rework old problems without referring to notes and see how far you can get without looking Focus on points where you get stuck!!! Final Exam Study Tips sheet is posted online (lots of helpful tips, be sure to look it over)!

8 What to Review EVERYTHING!!!!!! Textbook problems Lon-Capa problems Exams I, II, and III Practice exams for Exams I, II, and III Lab Reports Lecture slides TA discussion notes/practice problems ANY material covered during the course is fair game!!!

9 Clicker #1 Are you awake? Click A. A) yes E) no

10 WARNING: THIS REVIEW IS NOT COMPREHENSIVE!!!

11 The Atom Review Think about how the number of protons, neutrons and electrons affect the nature and properties of different atoms

12 The Atom Consists of small tightly packed nucleus surrounded by large cloud of electrons Nucleus contains positively charged protons and neutrons (no charge) Negatively charged electrons occupy very large volume compared to nucleus Mass of atom is made up mainly of mass of protons and neutrons (mass of electrons is so small that it can be ignored in total mass of atom)

13 The Atom The ATOMIC NUMBER tells how many protons are in nucleus In neutral atom, number of protons and electrons is the same Number of neutrons can be determined from mass number (mass number atomic number = # of neutrons)

14 The Atom Modern atomic theory is based on Bohr s model of the atom Bohr s model falls short because it does not take into account electron-electron repulsions Bohr s model also proposed quantized energy levels for electrons Electrons can only absorb or release energy in certain amounts and can only exist in specific energy levels Wavelike properties of electrons used to predict most likely location of electrons Regions of probability called orbitals

15 Rules for determining orbitals 1. Primary energy level starts with one type of orbital; each increasing energy level has one more type of orbital 2. There are an odd number of orbitals for each type of orbital 3. 2 electrons can occupy each orbital Energy level Regions of probability (orbitals) # of orbitals total # electrons N = 1 1 type of orbital (s) 1 2 N = 2 2 types of orbitals (s, p) 3 6 N = 3 3 types of orbitals (s, p, d) 5 10 N = 4 4 types of orbitals (s, p, d, f) 7 14 Look back in notes (Lecture #24) for chart on filling order for orbitals!

16 Properties of atoms Ionization energy energy needed to remove an electron from an atom or ion Electronegativity the attraction an atom or ion has for electrons Both of these properties are affected by how close the electrons are to the nucleus (positive charge of protons) The closer an electron is to the nucleus, the more it feels the pull of the positive charge of the protons If the electrons are being pulled more tightly, it takes more energy to overcome the attraction and remove an electron

17 Atomic Trends Remember: Trends are determined by number of protons and quantum energy level Atomic size increases Ionization energy decreases Electronegativity decreases Atomic size increases Ionization energy decreases Electronegativity decreases OVERALL TREND!

18 Isoelectronic species Isoelectronic: having the same number of electrons (same electron configuration) Since all of the isoelectronic species have the same electron configuration, cannot use periodic table trends to predict properties Have to consider number of protons to determine properties

19 Ionization and atomic size When an electron is removed, there is still the same number of protons; overall larger relative positive charge pulls remaining electrons in tighter When an electron is added, there is still the same number of protons; overall larger relative negative charge means electrons are bound less tightly

20 Clicker #2 Still awake? Click A. A) Yes. E) NO.

21 The Molecule Review Think about how the properties of the atom (that we just discussed) affect bonding between atoms and how that affects the characteristics of the resulting molecule

22 Types of Molecules Atom: smallest part of an element that is still that element (fundamental unit of which elements are composed). Atomic element: single atom of that element (noble gases) Molecule: Two or more atoms joined and acting as a unit. (element or compound) Molecular element: molecules composed of one element (H 2 ) Compound: composed of atoms from two or more elements (H 2 O)

23 Types of Bonding Think of bonding as a continuum (on a scale: not always just one type of bond) Large difference in electronegativity No difference in electronegativity Ionic (NaCl) Very polar! Type of bonding Polar Covalent (HF) Nonpolar Covalent (H 2 ) In general: the closer two atoms are on the periodic table, the more covalent their bonding is

24 Ionic Bonding Between metal and non-metal ions Transfer of electrons (no sharing!) Notice that valence shells are filled (noble gas configuration)

25 Covalent Bonding Sharing of valence electrons between two atoms Valence electrons spend majority of time in between the two atoms so that both atoms have a noble gas configuration (not the cause of bonding, just a way to remember) This sharing of electrons lowers the energy between the two nuclei Distribution of electrons is affected by electronegativity of the two bonded atoms

26 Nonpolar covalent bonds Example: H 2 Both H atoms have same electronegativity, so they pull electrons equally Electrons are distributed evenly around both atoms

27 Polar covalent bonds Example: HF H: very low electronegativity F: very high electronegativity Electrons are distributed more around F, resulting in partial negative charge around F and partial positive charge around H Indicated by dipole moment on bond

28 Determining Polarity First: draw Lewis structure for molecule PLACE ALL VALENCE ELECTRONS BEFORE ADDING MULTIPLE BONDS!! FOLLOW OCTET RULES!!! Second: determine geometry (how atoms and lone pairs are arranged around central atom) Use VSEPR Theory, to minimize electron-electron repulsion Third: determine shape of molecule (how does molecule look with just atoms, not including lone pairs) Fourth: Ask yourself - is the molecule symmetrical? RE-MEMORIZE CHARTS ON PP IN LAB BOOK!

29 Resonance If more than one possible structure can be drawn, then resonance can occur Multiple sharing of electrons can occur between more than one pair of atoms Since electrons are always moving, sharing can alternate between different pairs of atoms

30 Percent Composition Percent composition is based on ratios of elements in a molecule (subscripts) so it is independent of the amount of a substance Mass of part * 100% = % composition by mass Mass of whole Can use % composition to determine empirical formula of compound (lowest ratio of subscripts for atoms in molecule) If molar mass is known, then molecular formula can be determined from empirical formula (actual formula for compound)

31 Substances and Mixtures Pure substance: constant composition (elements or compounds) Could potentially be in two different physical states, and still be a pure substance (ice water) Mixture: Two or more pure substances remaining independent of each other Homogeneous mixtures same throughout; no matter what part you take, it s the same (sugar water, air) Heterogeneous mixtures has different properties from those of other regions (oil/vinegar salad dressing)

32 Intermolecular Forces London Dispersion Forces: all molecules have LDF, but is only type of intermolecular interaction found in nonpolar molecules and noble gases Dipole-Dipole Interactions: Occurs with polar molecules; the more polar the molecule, the greater the dipole-dipole interaction Hydrogen bonding: Special type of dipole-dipole, only occurs when H is directly connected to N, O, or F Ion-ion interactions: Occur between ionic compounds Ranking by strength of interaction: Ion-ion > H bonding > dipole-dipole > LDF When two molecules have only LDF, use molar mass to determine which one has stronger interactions

33 Determining Physical Properties When ranking substances to determine properties like melting/freezing point and boiling point: Stronger interactions: higher melting/freezing and boiling points (most likely a solid at room temperature) Weaker interactions: lower melting/freezing and boiling points (most likely a gas at room temperature)

34 General Solubility Solute substance being dissolved Solvent substance that is doing the dissolving How does polarity help us determine solubility? Like dissolves like! Polar solutes dissolve in polar solvents Nonpolar solutes dissolve in nonpolar solvents

35 Clicker #3 Click A. A) OK. E) NO.

36 Gas Laws Review Use common sense when thinking about gas properties and their relationships! Think about how changes in moles and temperature affect pressure and volume.

37 P, V, n and T V is directly proportional to n V is directly proportional to T P is directly proportional to n P is directly proportional to T P is inversely proportional to V P is proportional to 1/V V is proportional to 1/P

38 Ideal Gas Law The ideal gas law tells us the what about gases (what we observe), it does not explain why we observe what we do PV = nrt If P is in atm, V in L, n in mol, T in K, then R = L atm/mol K BE ABLE TO DERIVE THIS LAW TO SOLVE FOR ANY VARIABLE!!! P, V, n, T or any combination of these (ex. density) Remember that since gas particles are assumed to not interact with each other, their pressures are additive (partial pressures): P (total) = P 1 + P 2 +P 3.

39 Kinetic Molecular Theory (Assumptions) Gases consist of tiny particles (atoms or molecules). These particles are so small, compared with the distances between them, that the volume (size) of the individual particles can be assumed to be negligible (zero). The particles are in constant random motion, colliding with the walls of the container. These collisions with the walls cause the pressure exerted by the gas. The particles are assumed not to attract or to repel each other. The average kinetic energy of the gas particles is directly proportional to the Kelvin temperature of the gas. Assumptions are more likely to be true under: high temperature, large volume, low pressure, less attractive forces (nonpolar molecules)

40 Chemical Reactions Review Think about how energy states affect the outcome of a chemical change; remember how we can determine the outcome of a chemical reaction!

41 Significant Figures When measuring an amount in lab, the data you record can only be as accurate as the instrument or piece of equipment you used to measure it with When determining how many figures to use, look to the instrument with the least sensitive measurement Example: if you combine 63 ml of water from a 100 ml beaker (10 ml markings) and 12.3 ml of water from a 25 ml graduated cylinder (0.5 ml markings), you cannot report 75.3 ml of water! Since beaker has least sensitive measurement (could be 63 ml, or 62 ml, or 64 ml) the most accurate measurement of the combination of these two could only be reported to the nearest 1 ml (75 ml)

42 Chemical changes Physical change: change in one or more physical properties, but no change in fundamental components Changes of state (solid, liquid, gas) Chemical change: change in fundamental components of the substance Create something new/different; rearrangement of atoms

43 Exothermic versus Endothermic Speed of particles decreases Energy flows out from system Temperature of system decreases Exothermic Speed of particles increases Energy flows into system Temperature of system increases Endothermic

44 Endothermic versus Exothermic Reaction will have an endothermic step (breaking bonds) and exothermic step (forming bonds) Overall reaction depends on sum of endothermic (energy input) and exothermic (energy output) processes If overall energy in > energy out = endothermic reaction If overall energy in < energy out = exothermic reaction

45 Moles and Molar Mass Need a way to be able to compare amounts (masses) of different elements or compounds Since the atoms of each element have different number of protons and neutrons, they all weigh different and cannot be compared directly! When we have x things (Avogadro s number), we refer to them collectively as a mole If we have a mole of an atom, the average relative mass of that atom can be represented in grams per mole (g/mol) This is what we refer to as molar mass Use to compare amounts of different atoms/molecules without worrying about differing atomic properties

46 Conversion to Moles Molar mass mass Ideal gas law # particles MOLES Gas properties (P,V,T) Avogadro s # volume concentration

47 Chemical Equations Formulas for reactants on left side, formulas for products on right side of equation (phases in parentheses) Coefficients represent ratios of reactants and products Have no meaning outside of the equation! Subscripts represent ratios of atoms in a molecule (% composition) To balance the equation in standard form, use the lowest whole number ratio for coefficients When balancing equations, make sure you have same number of each type of atom on both sides of equation Do not balance by changing the subscripts! Balance the least complicated molecule LAST!

48 Limiting Reactants Need to determine limiting reactant because it will determine how much product can be made (LIMITS the reaction) To find limiting reactants, need two pieces of information: Amount of each reactant (in moles) Ratios of reactants (coefficients from equation) To determine limiting reactant, calculate how much you NEED to react completely and compare to how much you HAVE Use coefficients as ratios to determine how much you NEED

49 Precipitation Reactions When aqueous solutions of ionic compounds are mixed, resulting in a solid that is insoluble in water (precipitate) Ionic compounds will separate into cations and anions in solution Swap anions to find products Use ionic charges to balance molecular formulas, then use coefficients to balance chemical equation Be sure to re-memorize polyatomic ions for exam!!! Solubility rules will be given on front page of exam (be sure to look them over though!)

50 Stoichiometry and Phases Be sure to note the phases of reactants and products when determining relative amounts and moles Note whether solutions, solids, liquids or gases are involved and remember how they behave! Properties of products are not necessarily like reactants (molar mass, density, etc)

51 Stoichiometry Flow Chart Aqueous solutions (Molarity, volume) Moles of ions Aqueous solutions (Molarity, volume) Gases (P,V,T) Moles reactant A Moles reactant B Etc Moles product X Moles product Y Etc A + 2B + 3X + Y + Gases (P,V,T) Coefficient RATIOS Limiting reactant Coefficient RATIOS Masses (grams) Masses (grams)

52 Clicker #4 Click A. A) OK. B) Wait. C) STOP. D) WHAT R U DOIN? E) STAHP.

53 Jay Cutler still sucks Somehow in spite of Jay Cutler, the Bears have a chance for a playoff spot Don t let your inner Jay Cutler hold you back from your playoff spot! It s never too late to start new study habits!!! Jonathan Daniel, Getty Images

54 Holiday Magic Demo Show Wednesday, December 12 th, 7:00pm Sunday, December 16 th, 2:00pm (located in 100 Noyes Lab) THANK YOU FOR A GREAT SEMESTER!!!