Chemblog!

Halloween: good, clean, wholesome fun! Enjoy the fun/parties tonight and then go to your local dentist.

AP: had our second Thermo exam; we finish Thermodynamics, complete with Entropy and Gibbs Free Energy, in April (a few weeks before the big AP Exam!).
For now, it's back to Quantum...I'll have assigned reading in the text, Chapter 7.1 and 7.2, and some questions to do tomorrow; I'll post some "never forget" questions also.

D/G: We (finally) got to the modern quantum mechanical model of the atom, specifically focusing on PrinciPAL energy levels, sublevels ( which are NOT separate FROM but part OF a princiPAL energy level), and orbitals (OF a given sublevel). These energy SUBLEVELS are THE solutions to the Schrodinger equation, which gives the possible energies of electron(s) in an atom.
We have a written exam on Thursday; BE PREPARED. If you have questions tomorrow, you can always email me, that's what our class email is for.

E: We focused on Bohr Models of the atom that could be drawn from modern quantum model electron configurations. We then introduced the Periodic Table, which is our NEW unit.

AP: continued our quantum unit with a review (evidence and conclusion) of the Rutherford and Thomson models of the atom. We then discussed various properties of waves, specifically electromagnetic waves: speed, frequency, wavelength, amplitude, intensity, total energy. Then we began to introduce the particle/packet/quantum/photon nature of light. That will lead to the most important equation of this unit: Planck's Equation.
Tomorrow, we have a test AND a lab or labs.

D/G: we started the quantum/wave mechanical model of the atom by discussing the wave nature of the electron, the Heisenberg Uncertainty Principle, and the Schroedinger equation. The solutions to this equation gave all of the ALLOWED energies that an electron can have in an atom of a given element. We will talk about these allowed energies and the regions (orbitals NOT ORBITS!!!!) in which an electron of a given energy will LIKELY be found.
Tonight, I will post a practice multiple choice test that covers most of what is on Friday's multiple choice test. I will also post the objectives for Thursday's written response exam. Make sure that you go over your last two tests and follow the test-taking advice that I gave in class today and in the past.
Remember, EVIDENCE: whatever was seen, felt, heard, tasted, touched, measured, experienced.
CONCLUSION: what logically accounts for the evidence; what you are logically forced to say as a result of the evidence.
DESCRIPTION: answers WHAT occurred.
EXPLANATION: answers HOW and/or WHY something occurred. In an explanation, keep asking and answering WHY/HOW until you reach an experimental law or fact that has no explanation, but rather, is a definition or generally true statement.
BEFORE you describe or explain something, DRAW AND LABEL a picture of what is occurring. That will help you give a properly detailed answer.
None of this matters if you MISREAD the question, which is why I require you to TAKE PAINS to identify the keywords and circle, underline, and/or highlight them. Many students waste time and receive NO points for writing about what is NOT asked for.

E: We had a practical day of practice for your forthcoming exam. We did mostly electron configuration, orbital diagrams, and excited vs. ground state problems as well as some element vs. compound vs. mixture review. There are two more tests this quarter. The LAB exam will be a multiple choice test given next Tuesday, Nov. 7. Your lab folder must be up to date at that time or you will receive a zero on the lab exam (by the end of the quarter, nobody can afford to lag behind in labs, ever).

D,G: we finished our explanation of how the Bohr Model accounts for the bright-line emission spectrum of Hydrogen and SOME of the emission lines of the other elements. However, Bohr's model didn't account for many of the energy differences that electrons experience when they undergo electron transitions. This had to do with electron-electron repulsion and also the fact that electrons also behave as.....WAVES! More on that on Monday as we do the quantum mechanical model of the atom.
We will have our next two tests on Thursday and Friday: one test is written response on atomic structure including the Bohr and Quantum Mechanical Models of the atom and the other test is multiple-choice on atomic concepts, matter, and energy. On the following Tuesday, the last test will assess what you learned in lab this quarter: it will be a multiple choice test on lab techniques and skills covered in our labs this quarter. So, you have at least 300 more points to earn this quarter.
E: We finished electron configurations and orbital diagrams for the first three periods of the periodic table. That's about as far as we can go with the Modern Quantum Mechanical model of the atom. (Of course, if you're curious, at extra help, you can always ask further questions about the model). We will be tested on the Bohr and Modern models as well as on question types that the class did not master from the last test....SOON. Maybe 5 people ( I congratulate these students who are clearly trying and regularly come to some of the DAILY opportunities for extra help) have come in to correct their last tests. The rest of you, what are you waiting for? This material is on the Regents so you should want to learn or clarify what you didn't learn before the last test. You will see those question types again. There is plenty of practice material assigned in the hw over the weekend. Do that hw and check your answers, you will be tested on it soon! We will do review on Monday so MAKE SURE that you have your blue and orange review books (do NOT tell me you forgot them after the bell has rung) as well as the blue text exercise manual.
For additional points to your average, I am assigning a graded hw. On page 1 of your orange review book, there is a list of chemistry vocabulary that you must PRECISELY know and use on the Regents. For HW, due Tuesday, NEATLY WRITE OUT (in block letters if your handwriting is not good/clear; do NOT HAND IN ANYTHING THAT IS TYPED) the definitions of these terms. Use the glossary of these terms in the back of the review book or the text. DO NOT abbreviate; use complete sentences and, if you want to help yourself know these terms, write or draw an example of each term, if possible. Do this simple assignment correctly and hand it in by Tuesday or you will not receive credit.

AP: finished our Thermo unit with a light discussion about energy sources and consumption. Ironically, in life, this topic is paramount and drives just about EVERYTHING that affects you. Food, fuel, technology, competition, "quality of life" vs. living in a cave or with the Amish, these things will be your daily concern and perhaps daily interest if you become a chemical engineer or physical chemist.
Our test on Tuesday will cover the unit including the 0th and 1st Laws of Thermo, Calorimetry, Hess's Law in all of its forms, Hess Law diagrams, Bond energies/Enthalpy change estimations, as well as a gas unit question or two.
Have a good weekend....bring an umbrella.

AP- thanks for racing back from the field...our truncated class turned into a slightly extended class (perhaps I made up the "lost" ten minutes from a certain class last week; still trying to block that out).
We did the ultimate marathon thermo problem...I'm glad we got to do the delta nRT substitution so that we could still calculate delta H even though we initially only had delta E as calculated from the heat released under constant volume conditions...we also further saw the difference between heat of formation and heat of reaction...we even talked about bond angle strain, which you won't hear again until you ace orgo chem in college.

D,G: we dug into the Bohr Model today by looking at the bright-line emission spectrum of hydrogen and relating the spectrum to the energy levels of the electrons in a hydrogen atom. Bohr saw that the electrons must ONLY have SPECIFIC amounts of energy in an atom. He called these electron energies "energy levels" and proposed that electrons could only ABSORB or EMIT quanta of energy EQUAL TO the DIFFERENCE in energy BETWEEN ANY two DIFFERENT principal energy levels in an atom. As an electron LOSES a SPECIFIC amount of energy as it undergoes a TRANSITION from a HIGHER principal energy level to a LOWER principal energy level, that exact amount of LOST energy is EMITTED as a PHOTON (quantum) of light energy.
The video is on the main class website.

E: We further discussed and practiced with the quantum/wave mechanical model of the atom. Worksheets and answers are online for additional practice.
We reviewed a few questions from the last test. One question that I didn't go over involved TWO Hydrogen atoms CHEMICALLY COMBINED. I don't recall ANYBODY getting that simple question right. ANYTHING that is made up of JUST ONE ELEMENT must be called AN ELEMENT! Most people called the two H atoms a MIXTURE!!! Just the word mixture, in English, means two or more DIFFERENT things mixed together. Clearly, two IDENTICAL Hydrogen atoms can't be a mixture.
Use your notes and your orange review book to see pictures that show the difference between an element, a compound, a homogeneous mixture (called a "solution"), and a heterogeneous mixture (YOU are a heterogeneous mixture).
Study for your next test.
I'm in early tomorrow, Day 4.

D/G Honors: we completed the evidence and explanation of the photoelectric effect experiment from Einstein which was consistent with Planck's Theory. In science, theories are not 100% definitively proved, but evidence can be shown to be consistent with a theory. Certainly, the evidence from the photoelectric effect was consistent with Planck's Quantum Theory of light/electromagnetic radiation.
We also showed further confirming evidence of Planck's Theory from the Compton Effect.
We now can use this information to explain the Bohr Model of the Atom.

Regents E: we further showed the Quantum Mechanical Model of the Atom: the Principal Energy Levels n= 1,2,3,4 etc. have one or more sublevels each: s, p, d, f...and each s sublevel has one spherical s orbital, each p sublevel has 3 dumbbell shaped p orbitals, each d sublevel has 5 (mostly) double dumbbell shaped d orbital and each f sublevel has 7 crazy-shaped f orbitals. There are a maximum of two electrons per orbital. For tomorrow and Friday, print out this periodic table so that you can keep track of the electron configurations.
Here you go, ENTER THE ORBITRON!
and here is a great electron configuration tutorial
and a helpful video (don't worry about the scientist's names, though)

We then wrote the electron configurations for the first 8 elements. These electron configurations tell us the regions of probability for electrons in the ground state of an atom. They also tell us the accurate and precise energy of each electron in the ground state of an atom. We will continue the electron configurations and orbital notations of the elements.

AP: we finished the Hess diagram and, from that, did a lattice energy calculation.
We then discussed bond dissociation energies (and AVERAGE bond dissociation energies for heteronuclear bonds). We then obtained good estimates of change in enthalpies of reactions by adding the total moles of bonds broken in a reaction times their respective BDE's to the total moles of bonds formed in a reaction times THE NEGATIVE of their respective BDE's (negative because BOND FORMATION IS ALWAYS EXOTHERMIC, NO EXCEPTIONS-a rarity in chem!).

files and recap to be posted at around 8PM...no rush if you don't get to them until tomorrow...
files are up, finally.
AP: finished Calorimetry...MAKE sure that you KNOW the difference between heat capacity and specific heat (capacity)...also know what molar heat capacity means...know the UNITS for each of those terms for consistency....be careful in a calorimetry problem that gives you the heat capacity of the calorimeter as well as the specific heat of the water put inside the heat capacitor to absorb some of the heat released from the reaction...the equation MUST include the absorption of heat by the calorimeter AND by the water!
We then took advantage of Hess's Law which takes advantage of H, enthalpy, which is a STATE function. In problems, you will be given ALL BUT ONE of the energy change quantities: IE, EA, Lattice Energy, Heats of sublimation, formation, hydration, etc.

You MUST know how to draw the diagrams properly: labels, units, and relatively to scale.

D, G: we discussed the Nobel Prize winning Photoelectric Effect experiment and explanation from Einstein, who used Planck's Theory to explain the experimental results. Einstein won the Nobel ONLY for this paper!! That's just sad.

E: We did more Bohr models of atoms and ions, more examples of ground and excited state configurations. Then, since there were some problems with the Bohr model, we introduced the modern quantum mechanical model of the atom (very brief intro, much more to see with that!).
Then we did the emission spectra lab; the writeup for that will likely be posted this weekend.

NOTE: E and D Periods- the Safety and Density LABS are both due tomorrow in lab. They must be done perfectly and correctly. They must be put into your lab folder, which I will collect. I am in 229 before school tomorrow if you have questions.

G, D Honors: We reviewed the electromagnetic spectrum and colors of objects with respect to absorption and reflection of various colors of light. We then discussed "blackbody radiation" and Planck's interpretation of the blackbody radiation graph of intensity of EMISSION versus wavelength (or frequency) of electromagnetic radiation. His simple assumption is that ANY color/frequency of light comes in tiny indivisible packets/particles of energy. Each light packet/particle, which is the smallest amount of energy of any given color/frequency, is ONE QUANTUM (or photon) of that color of light. So, light has a dual nature: in Young's Double Slit Experiment, light behaves like as wave, BUT, in the blackbody radiation experiment, light shows its particle nature: it consists of separate, individual, mass-less particles called "quanta" (photons).
I will grade last week's test throughout the week and advise you as to success (I hope) or lack thereof.

E: We did many examples of the Bohr Model of the Atom involving ELECTRON TRANSITIONS from the ground state to an excited state ( as a result of the absorption of energy by an electron). We also showed electron transitions from an excited state to a LOWER energy state (which may or may not be the ground state): when an electron thus decreases in energy, it releases the lost energy in the form of light i.e. a photon which has energy EXACTLY equal to the difference in energy between the two energy levels that the electron traveled to and from, respectively.
On the last test, whether you studied or not, it is obvious that many of you did NOT use proper test-taking techniques in approaching the test. If you do not at least try to improve your test-taking skills, you are wasting an opportunity to better yourself as a student. When you CAREFULLY read a question and identify the key words, DO NOT LOOK AT THE ANSWER CHOICES! Treat the test as if it were a written-response test and predict or solve for an answer. THEN, look for a matching choice. So many of you are falling for TRAP answers because you are just picking the first answer choice that looks okay WITHOUT EVEN reading the remaining choices (I can tell!). Do not forget to apply this technique on your next test!

AP: we went over some common avoidable errors from the last test. We did an example of constant pressure calorimetry; then, we did an example in which the specific heat of a substance is determined. We also did a bomb calorimetry example. We just have to do integrate Calorimetry with Hess's Law and we'll almost be done with Thermo. We also have to do Hess Law Diagrams and Bond Energy calculations.

Thomas Young's Double Slit Experiment showing the wave nature of light



Another animation of Thomas Young's Double Slit Experiment showing the wave nature of light


Even more constructive and destructive wave interference

Honors: most of the questions on tomorrow's test come from the posted objectives but we have done THREE days of material since those objectives were posted; so expect a question on whatever was covered on waves. Significant figures will be tested on any question that involves a calculation.

Today, we discussed wave amplitude and its relation to intensity; then, we saw and heard constructive and destructive interference of waves. We discussed the visible part of the electromagnetic spectrum and the color wheel.

Regents: We covered the MAIN part of the Bohr Model showing the relationship between the light emission spectrum of hydrogen atoms and the possible energy levels that an electron can have.
The test tomorrow covers the material from the last test that we went over in test review as well as the Dalton, Thomson, Rutherford and Bohr models of the atom as well as sig figs and scientific notation.

AP: Our "abbreviated" class (MEA CULPA! - I promise bagels or doughnuts as just compensation) discussed Calorimetry and its relation to the first law of thermo. We discussed specific heat capacity and molar heat capacity; then, time ran out. We will finish Thermochem on Monday and/or Tuesday.

Since today's class was shortened, there won't be calorimetry on tomorrow's exam. There will be questions on everything else that we covered in thermochem as well as the explanations of the gas laws, gas stoichiometry, van der waal's equation w/ explanation of the constants in the equation, Graham's Law and rms-average molecular speeds and one more general stoichiometry problem.

http://www.livescience.com/forcesofnature/061017_ap_heavy_element.html
Do NOT think that making element 118 (will they call it Cicaleum???) has anything to do with chemical reactions, though.
This is high energy NUCLEAR PHYSICS. However, chemists DO get a new element to play with.
p.s. AP Class: I made a typo on the hw: text reading this week should have covered Chapter 6 sections 1 through 5 and 7 through 9. Section 6 is on Calorimetry which we will cover on Thursday.

D,G Honors: continued our long intro to the Bohr Model by discussing waves and electromagnetic radiation. There are powerpoints online that provide visuals for our notes. Talked about wavelength, frequency, and speed of waves; "c" is the symbol for the speed of light/any electromagnetic wave of radiation. We calculated wavelengths of various frequencies of electromagnetic waves from FM radio stations.
Thursday, we will discuss additional aspects of waves such as amplitude, intensity, energy, and "wave interference".
Kudos to those who came to extra help and realized the level of explanation required for Friday's test. Based on past class feedback, those who don't practice writing out, over the next two days, DETAILED, specific explanations and descriptions as listed in the test objectives will likely do poorly or not finish the test on Friday. No joke, the next two tests are difficult for most students yet the tests entail writing EXACTLY what was REPEATEDLY described and explained in class. You should definitely see me at extra help if you are unsure of the adequacy of your responses. Another reason to practice writing: YOUR SPELLING and GRAMMAR WILL BE CRITICALLY CHECKED AND GRADED! If you MISSPELL ANY OF THE WORDS FROM THE FILE ( of key words that you may not misspell) ON THE CLASS WEBSITE OR ANY OF THE KEY TERMS THAT WE HAVE USED IN THIS UNIT, POINTS WILL BE DEDUCTED.

Regents: our test has been moved to Friday for this ONE time - I will not usually schedule your test on the day of the Honors and AP class tests; as a result, I expect an A effort and a higher class average. If that doesn't occur, your next test will NOT BE ANNOUNCED.
Extra help may be very crowded on Thursday afternoon because the Honors and AP classes have their tests on Friday also. First come, first served with the questions that day. If extra help is too crowded at a given time, I have continuous extra help until the late buses leave so you can always check in later.

AP: We revisited the Van der Waal's gas equation and then did some stoichiometry of thermochemical equations, today. I will try to do some/most of calorimetry on Thursday. The test will be on material covered through Thursday including past tested and untested Gas Unit material and some built-in stoichiometry questions.

NOW I REMEMBER WHY MOST STUDENTS CAN'T APPLY HESS'S LAW: when I was writing out the solutions to the hw, I recalled that too many students try to do MASSIVE calculations ALL AT ONCE on their calculators without ANY estimate of what the answer should be. Do yourself a BIG FAVOR: before you calculate your Hess's Law answer with the crazy numbers from the data, ESTIMATE YOUR ANSWER BY ROUNDING ALL OF THE NUMBERS TO THE NEAREST TENs OR HUNDREDs place- WHATEVER IT TAKES TO DO THE CALCULATION IN YOUR HEAD!!! You should have a ballpark idea of your answer before you touch your calculator ESPECIALLY of whether your answer is POSITIVE or NEGATIVE. DEFINITELY practice the estimation of your answers and see how good you can get at that, quickly.
Then, DON'T do too much at once with your calculator!!! Get subtotals and then add or subtract as appropriate. THE SIGN CHANGES in the HESS law problems are the real KILLERS.
Mark me, heed my advice. Even the best have fallen on this only to wail, "what a STUPID error that was". I'm just telling you what most of my past students have said before they eventually became more careful. In the class and on the hw, I have tried to emphasize how NOT to repeat those errors (see hw answers on website). Good luck, I hope that we can prove that Hess's Law doesn't have to be messy.
Thanks.

Click on "Student Tutorials" on the left side of this linked page and enjoy various Gas Unit and Thermo unit tutorials.
http://cwx.prenhall.com/bookbind/pubbooks/petrucci8/chapter6/deluxe.html

http://cwx.prenhall.com/petrucci/medialib/media_portfolio/06.html

http://cwx.prenhall.com/bookbind/pubbooks/petrucci8/chapter7/deluxe.html

AP: revisited the First Law of Thermo : delta E = q + w ...be wary of the SIGN of q and w based on the conditions given for the process.
We discussed enthalpy which is defined as the heat lost or gained during a CONSTANT PRESSURE conditions. We distinguished between a STATE FUNCTION (P,V,T,E,H,S,G ...all CAPS) and a function that is PATH dependent such as work or heat ( w or q ).


We then went through three algebraic axioms for manipulating delta H when you multiply or flip a balanced thermochemical equation.
We will be using those logical rules when we start doing the alternate form of Hess's Law.
Tomorrow, we will get into how delta H values are experimentally obtained.
Friday is day 6...test day for the Thermo and Gas Units.

Regents: We finished our significant figure and scientific notation lesson. Then, we finished up the evidence that led to the Rutherford Model of the atom; study that picture on page 2 of the orange review book.
Always bring your orange review book and the blue workbook to class; starting tomorrow, we will use them almost daily.

Honors D,G: We finished our significant figure and scientific notation lesson; then we began our introduction to the Bohr Model of the Atom. In order to understand the Bohr Model, you have to know about radiant energy/light; what it is and how it interacts with matter. We will discuss light over the next one or two classes and then relate that information to the light emission spectrum of hydrogen (and other elements) in order to understand the Bohr Model of the atom. I will put up some PowerPoints on that. Tonight, I will also put up some outline notes that you can download and then expand upon as we discuss the Bohr Model in class. I will post the objectives for Friday's Honors exam (yes, it will be given Friday). Start writing your answers to the questions ASAP and then check them at extra help.
G Period: Bring in your LAB FOLDER with the completed LAB SAFETY agreement and lab questions tomorrow, TUESDAY.

I will post a density lab write-up for the Honors and Regents classes by Wednesday. That lab writeup will be due next week.

Honors and Regents: homework is from both the text and the orange review book as well as from some posted worksheets. There are a LOT of questions but all answers/solutions are posted so you don't have to finish the hw this weekend but get it done within the next three days and carefully check your answers.

Honors: Soon, I will post the objectives/questions for the next exam (which will be given on Thursday or Friday). You will see that the objectives are exactly what we have covered in class (IF you took good notes in class).

AP: I have posted some solved Hess Law problems and the Thermo Unit CollegeBoard Objectives for your perusal.

Since we didn't have time to discuss the exam today, here's some of what needs to be said:
As I graded the Honors Atomic Concepts I Exam, I could plainly see that the majority of you had never been held accountable for following directions. The one in five students who scored in the high 90s applied the information exactly as we had done in class. Those students also explicitly followed the test instructions.

In class, without exception, I modeled every atom-mole-mass problem with proper units, cancellations, and notation. I repeatedly warned that units were required for EVERY calculation on EVERY exam in this class. I explained that a number without a unit is NOT a measurement and is therefore meaningless in most calculations involving measured quantities. I even said DURING THE EXAM that the numbers used should match the decimal places from the data in the question. The next test will be much more challenging because most of the questions require explicit and detailed explanations; also, significant figures will matter in your calculations, now. On future tests, take heed of my advice or the poor grades will continue.

I have stated since day ONE that there are NO makeup tests and NO extra credit in this course. That means you should do your utmost to prepare BEFORE each test or quiz because these assessments are the reflections of your knowledge. One should NEVER expect extra credit in ANY course unless one first earns the BASIC credit from the tests in the course.

I am NOT saying that chemistry is easy, but an Honors student should prepare until the material is bulletproof and understood backwards and forwards before a test. Perhaps some of you do not have or will not make available the time required to achieve such understanding. I stayed after school every day and I would occasionally have one or two students come in with a couple of questions. I was in at 7:30 on days 1 and 4 and nobody showed even after all the buses were in.
Here are some of the major wanton flaws that were handed in on this exam; these errors should not be made by a true "Honors" student:

Ignorance of the meaning of mass number (recall that I said over 40 times that a mass number is really the proton plus neutron number)- you simply had to ADD the number of protons and neutrons instead of wasting your time looking up ATOMIC MASS (which clearly is a different phrase than "mass number") in the periodic table. Had you done the practice files and hw, you would repeatedly have seen the complete difference between atomic mass and mass number.
The chart on question 2 EXPLICITLY AND PLAINLY stated that the symbol had to include any NET CHARGE and the MASS NUMBER of the isotopes (as based on the sum of the protons and neutrons in that row of the table). MOST of you put NOTHING for either charge or mass and some of you put the wrong symbol which was PLAINLY on the Periodic Table that has a legend indicating the atomic number for each element.
There was no understanding of the difference between the law of constant composition (by mass) and the law of multiple proportions. See the notes: these laws are very different- one law requires one compound, the other law requires at least two compounds.
In the math calculation section, if units were even used, many times they were used inconsistently or illogically. Any time that units do not match perfectly, numerator with numerator, denominator with denominator, your answer will be WRONG. I stated that repeatedly and was ignored by many. Many people had impossible answers such as 8.398 atoms of Ne. Atoms are INDIVISIBLE! You can have 8 atoms or 9 atoms but NEVER 8.398 atoms.
Do not shorten or abbreviate the data from a question, EVER. If the question says that you have 24.00 g of Carbon, do NOT shorten that to 24 g or, even worse, to just 24. 24 is a TV show!
The bottom line is that many of you have no idea how much you need to practice to succeed in this course. NONE of you are starting on an even playing field. Some have to compensate a lot more than others in order to know the material in this course. Knowing chemistry requires much more than mere memorization although memorization is absolutely a basic essential; you have to know the HOW and WHY even for setting up a calculation.
Start preparing for the next test and come to extra help PREPARED with questions.

Another truncated day but at least we learned a concrete skill or two:
Honors and Regents: you were introduced to significant figures, "sig figs". Everyone seemed to catch on but I know from experience that you can forget that information if you don't practice with it. So, this weekend, I will post some sig fig practice files that have addition and multiplication of sig figs. I will finish sig figs and scientific notation on Monday; then it's back to Atomic Models. There will most likely be a test next THURSDAY. We are OFF on Wednesday so make sure that you study adequately over the weekend and also early next week.
I returned the Honors Atomic Concepts exams (some students in G still have to pick up their tests; avoiding them is not a good idea since you could have reviewed them over the weekend). I will return last week's Regents class exam on Monday.
IF YOU DID NOT DO WELL on your exam in Honors or Regents, I expect to see you at extra help correcting your mistakes and asking questions for clarification. That is why I am in 229 after school EVERY DAY; yet, very few have come to extra help even though some of you need extra help almost daily. Even if your average is low, don't make things worse by never learning the material that you should have learned by test day. Most of chemistry is cumulative so you will dig yourself into an inescapable hole if you don't correct your mistakes and eventually learn the material. At least you'll earn some credit back when you know the information on the Regents exam, otherwise you'll be going to summer school.

Now that we have the Orange Review Books, I will post some review hw and answers for you to check. Many of you still need to clarify the difference between atomic mass and mass number and to know what atomic number means. I will also post answers to the text Chapter 4 Unit questions.

AP: Just a skeletal lesson on enthalpy of formation, enthalpy of REACTION (NOT the same as FORMATION!), and Hess's Law. No joke, most students from the past two years REFUSED to put the coefficients from the balanced equation into the Hess formula. Please write out the general formula and follow it exactly; this doesn't have to be a difficult unit.

We conclude our abbreviated week with Pep Rally Day tomorrow. Good times.
Our classes are cut short so be ready to work fast as soon as class begins.

AP: we did another descriptive chem set drill; take good notes on all of the sets including any mention of colors or other physical properties of reactants or products (e.g. iodine solid is dark gray; iodine vapor is purple; SO2 gas has harsh, toxic fumes that cause choking).
We started thermochem and introduced the concept of universe= system + surroundings (the equals sign means "duh"). We talked about work, heat, and changes in internal energy; we discussed the Zeroth and 1st Law of Thermodynamics: energy can neither be created nor destroyed a.k.a. deltaE = q + w . More on that important law tomorrow.

Honors: D,G covered the Rutherford Gold Foil Experiment evidence and inferences/conclusions; download the videos of that from the class website, study and enjoy! In D Period, we began to discuss the next major improvement in the atomic model: the Bohr Model of the atom. I will give out the Orange Review Books tomorrow.

Regents: we explained the Thomson Cathode Ray tube experiment (see videos on website) and then the Rutherford Gold Foil Experiment, which we will continue tomorrow. Watch the Rutherford video from the class website. I will give out the Orange Review Books tomorrow and I will assign some review questions and some grams to moles to atoms questions from that book. If you have the Barron's Blue Review Book, check that you have the 4th Edition because that edition has the correctly assigned page numbers for hw.

I will try to have all Regents and Honors tests returned by tomorrow. In Honors, although there are about 12 scores in the 90s, there are a lot of outright failures due to an OBVIOUS lack of preparation and failure to follow directions. OWN your mistakes and make sure that they aren't repeated. That's the most important thing that you can do in this course.
I should have the AP exams graded by Friday.

G, D Honors: finished the evidence and conclusions of Thomson's experiments that led to the "Plum Pudding" Model of the atom. Thomson also used his measurements to deduce the charge to mass ratio of an electron; that, along with Millikan's Oil Drop experiment that deduced the charge of an electron, led to the calculation of the mass of an electron.
We will further discuss the experiment that led to the more accurate AND precise Rutherford model of the atom.

E: finished up gram to mole to atom and vice-versa calculations. Make SURE that you know how to set up these calculations AND that you know how to use your SCIENTIFIC calculator for them (NO graphing calculators will be permitted on any future exam).
We will discuss the evolution of the models of the atom on Thursday and Friday- see Chapter 4.2 of the text.

AP: finished the Van der Waals equation for real gases and explained the meaning of the a and b correction factors and how to predict their relative magnitudes. Try the descriptive chem set tonight. We will discuss that tomorrrow and then we will start THERMOCHEM...it's all about energy changes during reactions and phase changes.

AP, Honors, and Regents classes:
I haven't yet been able to post hw and powerpoint files for any classes tonight so just review notes from today for hw. Later tonight, I will post all files that can be done for hw tomorrow. G'night.
update: very long day...
hw files and powerpoints are up for tomorrow...Honors and Regents classes should find the Atomic Concepts powerpoints helpful; the text does a pretty good job with its illustrations also. The Thomson audio and video files are posted too.

AP- had our Gas Law and Gas/Solution Stoichiometry exam today. Another long one but we have to cover the important question types...next test will have the missing Graham's Law questions and some more Gas Law explanations...

Honors: we started the important description and explanation of the major models of the atom: Dalton to Thomson and then later we will do Rutherford to Bohr to the Modern Quantum Mechanical Model of the atom.

Regents: we did some practical calculations involving the mole and the atomic mass scale.

AP: Reviewing all of the hw solutions and practice tests that I put up for this test, I see that the volume of practice material might be overwhelming. Too much of a good thing can sometimes have a negative effect.
Since our next exam (the exam AFTER the one tomorrow, Tuesday) will also have some gas unit questions, you can save many of the practice questions for that test. Just make sure that you know how to do the types of questions that we covered in class and also see the previous post for general objectives covered on this test.
See you tomorrow @ 7:30.

Now that I'm on-line (see rant below), I can give some general guidelines for the AP exam on Day 6, Tuesday. Of course, the most general guideline is that the test will cover class material- notes, text readings/problems, and practice tests- since our last exam as well as some accumulated skills from previous exams.
The exam is based on, but not limited to, the following items:

- redox balancing via the half-reaction method
- mixture problems (whichever method you prefer)
- percent composition or combustion analysis to empirical formula to molecular formula via scaling factor (show scaling factor calculation explicitly)
- gas stoichiometry with limiting reactants and percent yield
- each gas law as explained via kinetic molecular theory: know the four postulates of K-M theory and also explain each gas law EXPLICITLY and in MINUTE detail. Show cause and effect between each variable P,V,n, and T and the effect of each on the 1. particle collision frequency (number of collisions PER SECOND) with the container walls and 2. the average FORCE or energy of the particle collisions with the container walls . Some explanations require a two-part sequence. Drawings are permissible and strongly encouraged as part of a thorough explanation.
- Dalton's Law problems including gas calculations when gas is collected via water displacement.
- Graham's Law calculations for BOTH relative effusion rates and relative effusion TIMES
- Average (RMS) speed of gas molecules: don't forget the 1000g/kg conversion factor when you write your units in the equation from the tables! I warned you, do not mess up that calculation. If you get a molecules going a million meters per second, you did something horribly wrong. Most average molecular speeds at normal temperatures are in the hundreds of m/s range.

That's what I have for now. I am happy to say that the class was generally very strong on the last exam. If you correct your relatively minor errors (test-taking or other types) by seriously reviewing/analyzing your past exams, you will continue to get even stronger (in which case, awards may have to be invented and doled out)!

I have been out of radio contact due to a temporary shutdown of my expensive Cablevision service. For the third time this year, Cablevision had ineptly shut off my "Optimum" Online service. I finally spoke to a live human after sitting through ten minutes of push-button options and five minutes of inane ads for the most puerile pay-per-view events (yes, I really want to waste my life watching "extreme" wrestling). What happened this time? Well, the first two reps told me that there was a "problem" and that they would "work on it" and I should have my service back "by the morning". Two days later, still with no internet service, I finally spoke to a rep (who clearly understood me and whom I could clearly understand- wow, what an asset to have in customer service!) who told me straight-up that I had "moved" and had cancelled my internet AND TV service. I replied that I had done none of those things and that I would like to know how such a change could occur without my knowledge. Well after receiving no explanation or apology (of course, I don't blame that one, helpful rep AT ALL because she was the only one who knew what she was doing), my internet service has returned. If there are cable providers other than the monopolistic Cablevision, I will sign with them forthwith. Don't suggest DSL, that's even worse.

E- Regents: We're starting to move up although there is room for improvement; many of you still do not know how to take a test, which translates to lots of careless errors and inconsistencies. Come to extra help and we'll talk more about how to take a test to maximize your score.
Class average: 83 (7 more points, about two more correct answers per test, and I'll/we'll be happy)

D, G: I'll be grading your first Atomic Concepts exam over the next week. I was glad to hear that some found the test easy or easi-er than the last exam. I did note one disturbing and truly inexcusable mistake on some tests: recall the highly inappropriately named term, "MASS NUMBER". I did not invent that term and I wish that the name had never made its way into chemistry texts. However, I ranted on and on about how that term REALLY means "the number of PROTONS + NEUTRONS in the nucleus" of an isotope of an element and that the terms has NOTHING, per se ("by itself"), to do with the mass of an atom! Therefore, the "mass number" CANNOT POSSIBLY BE A DECIMAL (non-integer)! THERE ARE ONLY WHOLE NUMBERS OF PROTONS AND NEUTRONS in a nucleus or anywhere! YOU WILL NEVER, EVER SEE A "mass number" THAT IS NOT A POSITIVE INTEGER (even if you do crazy nuclear physics)! I went on and on about how the MASS NUMBER is NOT the MASS of the atom!
When I go out of my way to help you avoid the mistakes of legions of past students, I expect you to NOT make those mistakes. I could not have highlighted the mass number misnomer any further. If you did practice problems, you definitely would have repeatedly written and seen the difference between a mass number and an atomic mass.
Furthermore, we did problems for a WHOLE WEEK in which we calculated the (weighted average) ATOMIC MASS of an element. That number is THE MASS of an AVERAGE atom of a given element. ATOMIC MASS = MASS OF (average) ATOM!! These numbers ALWAYS HAVE DECIMALS (with ONE exception: the atomic mass of the Carbon-12 isotope is, BY DEFINITION, exactly 12 amu).
Here is an example of what I am talking about:
the MASS NUMBER ( =total of protons + neutrons) of a chlorine-37 atom/isotope is 37. The MASS of a SINGLE specific atom of chlorine-37 is 36.98 a.m.u. or grams per mole (measured to the hundredths place). YET, the ATOMIC MASS of chlorine, in general, is 35.453 a.m.u. (or grams per mole) because there are two isotopes of Cl, Cl-35 and Cl-37 and the WEIGHTED AVERAGE of those two isotopes is 35.453 a.m.u. (or grams per mole). The ATOMIC MASS of any element is the weighted average of the masses of the isotopes of that element. The ATOMIC MASS never turns out, even coincidentally, to be a whole number / integer (unless you are intentionally rounding your answer to the one's place).
If you made the above error, make SURE that you learn from that error and don't repeat it on future tests because you will have to know the distinction between mass number and atomic mass for the rest of this course.

AP: we almost wrapped up the gas unit as we applied the equation for the average (root-mean-squared) speed of a given type of gas molecule at a particular temperature. Remember that the formula given in the reference table is "WRONG": you have to multiply the numerator by 1000 grams per kilogram) in order to use "normal" molar mass units (grams per mole).
Also, of course, only Kelvin/Absolute temperatures "work". We then applied the two versions, relative rate and then relative time, of Graham's Law of Effusion. Be careful to always write the GENERAL formula first and then, from the given data, plug in the respective values for each gas. Graham's Law is a simple equation but, MARK MY WORDS, MOST students cannot apply it properly and consistently. They forget the square root or they write the gases in reverse order or they forget to "square" the square root when the variable is in the square root or they square only one side of the equation. Please QUALITATIVELY estimate your answers to these questions BEFORE you do ANY formal calculation. If you KNOW that a heavier gas effuses more slowly, then its rate is slower (lesser) BUT ITS EFFUSION TIME IS longer (greater!). Make sure that your answer is consistent with your guess. If you are solving for molar mass, remember, the lightest gas in the entire universe is MOLECULAR HYDROGEN! So, if you get a molar mass of less than 2.0158 grams per mole, you are wrong.

Dare to gaze at the face of the awesome yet pulchritudinally challenged Amadeo Avogadro!
G and D Honors: we only had half of a period today so I didn't bother to start the next part of our unit. We'll begin that next Tuesday. We did a review lesson today (rarely will we have time for this) and did a couple of problems converting atoms to moles to grams and vice-versa.

E: we did one more Law of Multiple Proportions problem today and then we talked about the atomic mass scale and the mole.

AP: got into the amazing Cannizzaro method for identifying an unkown element in a compound via gravimetric analysis of the elements in the compound. From the data, we obtain some whole number multiple (1x, 2x, 3x, etc.) of the atomic mass of the unknown element.

Good luck to the Regents and Honors classes on their chem tests tomorrow!

AP: applied Dalton's Law to two "collection of gas over water" stoichiometry problems; good point that all gases in a mixture occupy the ENTIRE volume of the container so you just have to use a single value for V for all gases in any given calculation.
We began our first of many descriptive chemistry sets...make sure that you re-write those and try to GENERALIZE each reaction so that you recognize them when the elements are slightly change i.e. using Cl2 instead of Br2 in a single replacement of iodide ion.
We began one more partial pressure problem. Tomorrow, we do the amazing Cannizzaro Method for determining the atomic mass of an unknown in several compounds and then we'll try to finish the unit.

D,G Honors: we did atoms --> moles --> mass problems and the reverse mass-->moles--> atoms problems....these are ALWAYS two part problems; you CANNOT convert a number of atoms of an element to a mass (in grams) in one step and you CANNOT in ONE step convert a specific mass of a certain element to a specific number of atoms. Both calculation require you to calculate the number of MOLES of atoms of a substance. Once you know the number of MOLES of a substance, then you can easily convert the number of moles to the number of atoms or to the number of grams by using the appropriate ratio or conversion factor.

E: we finished up Dalton's Laws with the Law of Multiple Proportions. Make sure that you are READY for your second test of the semester, which is on THURSDAY. The test will be worth 100 points towards your quarterly average.

This Thursday, both Honors and Regents classes will have tests on all material covered since our last exam through what we cover in class on Wednesday. I will give further details in class.

G and D Honors:
We reviewed Dalton's Laws of Constant Composition and Multiple Proportions; I will dig up some worksheets on these laws and post them by tomorrow.
We then discussed the basis of the atomic mass scale. Don't freak out about that; practically speaking, you will be responsible for knowing simple conversions and ratios: for example, if one atom of Carbon "on average" weighs, 12.011 a.m.u., then a "mole" of Carbon atoms must weigh 12.011 grams....just replace the unit "a.m.u" with "grams" when you increase from one atom to one mole of atoms. The end.

Regents E: We reviewed Dalton's 4 Postulates on Atoms and then we did several examples of Dalton's Law of Constant/Definition Composition. We deduced whether two samples containing compounds of carbon and oxygen are actually samples of the same compound; we did this by applying the Law of Constant Composition.

AP: We finished some gas stoichiometry and then applied Dalton's Law of partial pressures to calculate the pressures of each component of a mixture of gaseous products. We then started another problem in which we will use the exact same law of partial pressures on a problem involving a mixture of gases collected over water (therefore, water vapor is always one of the gases in the mixture contributing to the total gas pressure of the mixture).
Tomorrow, we will hit that descriptive chem problem set and then cover one more gas law: Graham's Law of Effusion (done and done in Honors) and the Van der Waal's Gas Equation (child's play).