SciHawks

Physics - for HW, do Electrostatics A, questions 4 and 5. These explanations are similar to the ones that we did in class today so you should be able to figure them out; if not, there is extra help tomorrow morning before class.
We learned the MAJOR difference between a description and an explanation. The burden of proof in giving an explanation is much greater than that for a description because an explanation entails how and why something occurs; usually, there is a logical sequence of cause and effect events within an explanation. Explanations require precision/detail. To develop a proper explanation, always write the word "why?" or "how?" at the end of each sentence that you write, and then ANSWER that question, with a "because" sentence until you get to a statement of fact that cannot be further explained.

We did the first 3 questions in Electrostatics A, drawing and explaining (using our labeled drawings) how charges move when a charged object is near another object.

AP Chem - took our Bonding/Molecular Geometry unit exam.

Physics- we further discussed electrostatic charging via conduction, and then via induction.
We noted the structure of the atom to see that only the outermost/valence electrons can move in a given material, the protons can NEVER move throughout a substance because they are all held together to neutrons in the nucleus of each atom via the STRONG FORCE of nature which, conveniently, is the strongest force in nature by far, yet it only acts over short distances i.e. the diameter of the NUCLEUS of an atom, which is about 10^-15 m (teeny tiny!).
We finished up our Power Lab, and then began a lab on energy loss in an inelastic collision.
By measuring the potential energy of a lacrosse ball at a given height, and equating that to the kinetic energy of the ball as it hits the ground, and then measuring the (lower) potential energy as the ball returns to a new lower height, we can calculate the net energy lost during the collision of the ball with the floor - we certainly hear that some of the potential energy was converted to sound energy as the ball hits the floor.

We began to discuss the various types of solids by bond type.

Physics - started our new unit on Electrostatics.
Using an electroscope, we saw that objects could be charged via friction, and that charge (electrons) could be transferred via conduction. We also saw that we could move electrons via attraction to a positively charged object, or repulsion from a negatively charged object, even without touching the two objects i.e. via induction.

Physics - took part 2 of our Work and Energy unit exam.
There was a correction to the last question on the multiple choice; a newborn human infant cannot way 900 Newtons. Think of it this way, 1 kg is about 10 N of weight. So, to convert from Newtons to kg, just divide by 10, and vice-versa. A 90 kg baby at about 2 lbs. per kg would way 180 pounds! ouch.

For another rough approximation, there are about 5 Newtons to every 1 lb. of weight. So, if you weigh 100 lbs., in metric units, you weigh 500 N.

We finished the write-up for our power/bavaa lab.
On Monday, we start the next major section of Physics: Electricity and Magnetism (mostly electricity in our course). In a college course, this part of physics is given in a different semester.
We will have to do a lot of drawing because the particles that we will deal with are invisible; however, with the correct picture, the forces and other factors are not difficult to deal with. You just have to remember that like charges repel, and that opposite charges attract!

AP Chem - did a couple of reinforcement bonding/molecular geometry/hybridization , and IMFA examples.
We will continue on with the application of intermolecular forces of attraction (IMFA) in discussing solids, liquids, and gases before our break.
The Bonding unit exam will be given next Wednesday.
I will post more practice questions on Blackboard.

The question types on the next test will be as follows:

1.Most of our time and therefore most of our test will be on all of the types of molecules or ions that we drew out in our grand chart. So anything and everything on that chart will be asked for such as:

 - how to draw the correct Lewis dot structure including any and all reasonable (by the rules) resonance structures for any atom, molecule, or ion (given one central atom)

-Be able to show the orbital hybridization that occurs on a CENTRAL atom starting with the orbital diagram of the un-hybridized atom. Then show the electron shifts that occur in order to form the proper bonding arrangement in the molecule. For example, in CH4, carbon has a valence electron configuration of 2s2 2p2, which had only two unpaired electrons available for bonding. Not only that, the unpaired p electrons are in perpendicular p orbitals. So, in order to explain the four bonds that form in a tetrahedral arrangement, the C must hybridize its 2s and all three 2p orbitals to form FOUR equal energy, tetrahedrally oriented sp3 orbitals. As bonds form, these sp3 orbitals overlap with the Hydrogen 1s orbital (that is all that H has occupied with one electron; generally don't worry about hybridization of terminal atoms, unless there is only one type of hybridization that can apply) and the opposite spin electron pairs (one from each atom in this case) form a bond between each pair of atomic nuclei.
- know how to calculate and apply formal charge ( you must SHOW your calculation; the circle method is fine - bring a PENCIL for that part)  in determining the most significant resonance structure for a molecule or ion.

- how to determine bond order and its relation to bond length AND bond strength (BDE).

- know the rules for electron deficient species, odd-electron molecules, and expanded octets.

- explain the dimerization of odd-electron species/ radicals, and how/why they are relatively so reactive.

2. Be sure to draw OXOacids correctly: for OXOACIDS, each "H" in the formula IS NOT BONDED TO THE CENTRAL ATOM, but rather to one of the Oxygen terminal atoms, which is why they are called oxoacids. So, in nitric acid, HNO3, the H is bonded to one of the terminal oxygens that is bonded to the N. Don't forget that. Also, keep in mind that Lewis structures for ANY ions, whether monatomic or polyatomic ions, ALWAYS get put in brackets with the magnitude of the charge FIRST and the sign of the charge NEXT outside the brackets; do not say that ions are polar or nonpolar - ions have full INTEGER charges of just ONE sign. Ions can only form multiple bonds to all surrounding oppositely charged ions! Ions can ATTRACT molecules via ion-molecule (duh!) attractions.

3. covalent vs. ionic bonds vs. metallic bonds

4. Molecular polarity and its relation to IMFA- intermolecular forces of attraction - types
The polarity of covalent bonds may result in the formation of permanent dipoles in a molecule if:


there is a net PARTIAL positive region of a molecule with a net partial negative region on the opposite region of the molecule
- this usually results from dipoles that are NOT equal and opposite OR dipoles that, due to lack of symmetrical distribution, do NOT cancel out.


5. Explain and show resonance stabilization in a given molecule via valence bond theory/orbital hybridization, and by showing overlapping p orbitals containing a pair of electrons; the electrons in these overlapping p orbitals are above and below the 3 or more bonded atoms' nuclear plane.
Relate the fractional bond order to integer bond order lengths and strengths.

6. Know the difference between and the REASON for the relative strengths of sigma bonds and pi bonds.

7. For intermolecular attractions, know the different types: induced dipole, dipole-dipole, and extreme dipole-dipole (hydrogen "bonding") attractions. Based on electronic and molecular geometry from your Lewis structure and VSEPR, predict the molecular polarity and the expected dominant intermolecular types!! of attraction. For example, CF4 has tetrahedral electronic and molecular geometry, which results in a symmetric distribution of charge/electrons. The molecule is therefore nonpolar because there is, on average, no net partial positive or partial negative "side" of the molecule so its intermolecular forces of attraction are induced dipole attractions.
REMEMBER, BOTH polar and non-polar molecules have induced dipole attractions BUT polar molecules ADDITIONALLY have dipole-dipole or, if there is an H-F, H-O or H-N within the molecule, there will be EXTREME dipole-extreme dipole attractions among/between the molecules.

Physics - took part I of the Work and Energy unit exam.

AP Chem- did the remaining 5 and 6 electron-domain types of molecules and ions, emphasizing placement of any and all LONE PAIRS of electrons on the EQUATORIAL triangular plane in the 5 electron domain species.

We had to readjust our redox titration lab because the equivalence points had been reached after the addition of a mere 6 mL of titrant. We could have titrated MORE bleach solution or less dilute bleach solution but we decided that it would be easier or more practical to do a 1:5 dilution of the titrant, bringing our thiosulfate concentration to about .025M.

Physics - did work and energy multiple choice problems.
We then considered the (elastic) potential energy that is stored in a spring by virtue of its "stretch" or "compression" distance, x, from its equilibrium/un-stretched position.

The greater a spring is compressed or stretched, the greater the stored potential energy/ability to do work when the spring is released. The PE of the spring is proportional to the SQUARE of its stretched or compressed distance.

Our unit 6 test is on Thursday and Friday this week.

AP Chem - to give you more time and practice with this most important unit, I will give the unit exam sometime next week. I will post a list of question topics tomorrow or Thursday.

we looked at all important aspects of our electronic and molecular geometry, hybridization, molecular polarity chart today for each of AX3, AX2E, AX4, AX3E, AX2E2, AX5, and AX4E molecules (or ions) today.

We also explained resonance stabilization by using valence bond theory. We reviewed bond order, and its relation to bond strength and bond length.

Physics - did problems that involved conversions of potential energy to kinetic energy, and vice-versa, given that total energy is a constant, always!

We looked at "estimation problems", in which we use rough approximations of physical quantities to get a ballpark answer, and choose the closest matching answer. Estimation problems will appear on each test for the rest of the year.
It is important to practice and use scientific notation, so that these problems are more easily solved.

We looked at energy conversions in pendulum problems and noted that the speed of the bob does NOT depend on the mass of the bob! We saw that, as potential energy (mgh) of the bob was converted to kinetic energy (mv^2 / 2) , the masses cancel on each side of the equation.

AP Chem- showed orbital hybridizations for AX2 and AX3 type molecules.
We also showed, and discussed pi bonding in molecules.

Physics - start prepping for next week's work and energy unit exam - you have a three day weekend!
For hw: check Blackboard for solutions to Work and Energy 1- 4 problems that we did not get to in class. Do those problems from the packet and check your answers.
Today, we discussed all of the formulas for the unit, especially the all-encompassing change in total energy formula. Since energy cannot be created or destroyed, it can only convert from one form another, the total energy change in any object is always ZERO, which equals the sum of the changes in POTENTIAL, KINETIC, and INTERNAL energy.
We have the three formulas for potential, kinetic, and internal (due to frictional work) energy change, so we just let the questions tell us the one missing variable!

We will do problems on "estimates" of physical quantities, and some multiple choice practice on Monday.

AP Chem - notes and hw are now posted on Blackboard (12/10).
 we finished our discussion of the "smog" phenomenon by discussing kinetics, energy changes (thermodynamics), and observations of sky color to explain the greater smog content on warm summer days as opposed to cool winter days in NYC.
We went over other octet exception molecules : those containing H, Be, and B, which follow a duet, quartet, and sextet rule, respectively.
We then explained the insufficiency and inaccuracy of using atomic orbitals to explain the bonding in molecules. We use "valence bond theory", which involves VSEPR that causes orbital hybridization.
We went through the hybridization required for each of the possible electron domain numbers about a central atom.
We then began our chart of each of the possible electron domain molecules, starting with an AX2 example.

Physics - we did Work and Energy 4 problems involving potential and kinetic energy calculations.
We did a lab showing the power generated in your doing the work of lifting your body up stairs in a certain amount of time.

AP Chem - we showed how to draw Lewis structures for "odd-electron" molecules; everything is the same except that the central atom ultimately gets 7 valence electrons instead of 8.
We then explained the reason for the relatively increased reactivity of radicals (lone single electron containing molecules), which are stabilized by reacting with each other or other molecules by forming a bond between nuclei using their lone/single nonbonded electron.
We used the example of nitrogen dioxide reacting with another nitrogen dioxide molecule to form dinitrogen tetroxide. This process is called DIMERIZATION.

Physics - we showed the three ways that work done on an object can change its energy: potential ( work to change height), kinetic (work applied horizontally), and internal (work due to friction).
We did a work problem involving a frictionless ramp.
We also applied the definition of power, the rate at which work is done, to several problems involving work and time.

AP Chem - we reviewed the various types of intermolecular attractions, showing the requirement for extreme dipole dipole attractions (the inappropriately named "hydrogen bonding", in which there is no bond) is an extremely polar region of the molecule due to a highly polar covalent bond within each molecule between an H atom and either an F,O,or N atom (not Cl because that is a larger atom, so the resulting molecules do not pack close enough together for an extreme attraction).

We then discussed the made up "formal (fake, not real) charge" method with which the more/most significant resonance structure in a series of resonance structures may be determined. I teach this only because the method is on the AP exam- its worth may do more harm than good, but we have to know how to use it.

Physics - the Momentum and Circular Motion unit is extremely important. Some of you wasted two weeks of this course not learning the material, and not asking questions to help you to learn the material.
There was more help available for this test than for any previous test: the practice test, a lengthy set of worksheets in the packet with fully detailed answers, extra help before and after school. Why throw away a unit exam, when you can ace it with some practice, persistence, and repetition.
Be sure to go over the test, check the thorough answer key on Blackboard.
This material is emphasized on the Regents exam, and is central to understanding mechanics in Physics.
The big disappointment is that almost all of you have proven how well you can learn physics, when the pressure is on. Don't take a vacation when you do well on a previous test; use that psychological "momentum" to continue to do better and better.
Thank you.
Today we collected did the centripetal force requirement lab; we varied the INDEPENDENT variable, the Tension in the string, by attaching various masses to the string, which pull the string with the force of their weight/gravitational attraction to the earth.
Theoretically, the greater the centripetal force requirement, as supplied by the source- the tension on the string- the greater the velocity that can be sustained on the circular path.

We then did the same incline problem that we did on Friday except that this one had a frictional force between the block and the ramp. We saw that the total work done equalled the work done against gravity in the vertical direction plus the work done against friction all along the length of the ramp.

We also introduced the meaning/definition of power, the rate at which work is done.


4th/5th period - we discussed a method, a flawed but occasionally potentially useful (though distasteful) method of determining significance of a given resonance structure when there is no spectroscopic data (the best method) available.

Physics - we did a "work on an incline" problem in two ways, one involving more steps, the other involving fewer steps (the way that we will be doing future problems). We did so because we needed to establish the equivalence of the two methods.
We saw, for an object that has no NET change in its kinetic energy (started at rest, ended at rest, or any lack of net change in velocity) that the WORK on the object is solely equal to its change in GRAVITATIONAL potential energy (due to its change in height/position relative to the center of the Earth). This work is equal to the calculation of force applied to the object along the ramp (F parallel of the Fg/weight component) x the distance along the ramp.

We introduced the next problem that adds the factor that there is friction between the object and the ramp's surface.

Physics - took part 2 of our Unit 5 exam.
Began work on our "Work and Energy" unit by establishing their relationship, and reasoning through potential energy as the potential to do work; we did a few of the work= force x distance problems in units of N-m or Joules.

Physics - took the multiple choice part of our Unit 5 exam.

Tomorrow, we have the written response of the unit exam.
Expect the following question types (as seen in the packet and practice tests, etc.)

Momentum and Impulse - sticky/inelastic collisions, bouncy/elastic collisions, and explosion problems. Impulse causing change in momentum, causing change in velocity.

Circular Motion - questions relating period, radius, velocity, centipetal acceleration, centripetal force REQUIREMENT, the SOURCEs of centripetal force.

Elevator problems - Fnet, F (gravitational) or weight, and F (normal)- the reading on the scale.

AP Chem - we have a test on Friday involving non-stop explanations of periodic trends. On the last test, the "explanations" of the photoelectric effect, in general, were the worst that I can recall. Copying the question is not and cannot ever even remotely qualify as an explanation. As a reminder, explanations answer HOW and WHY phenomena occur; descriptions merely state WHAT occurs.

Most of you cannot and do not know how to write (or worse, memorize) an explanation. I implore you to write out your explanations and submit them to me for correction BEFORE Friday's exam.
DO NOT WRITE ANY EXPLANATION FROM MEMORY. Thoroughly and repeatedly study the notes on any explanation FIRST, then try to write a proper explanation.
The fact that you are not making sure that you are prepared for each test is astonishing. There has yet to be a surprise question of any type on any test. Thus, you should be checking that you understand the tested information correctly, AND that you can convery that knowledge IN WRITING and DRAWING on a test BEFORE you take that test.

Note: on the Periodicity Worksheets posted on Blackboard, some of the brief explanations were highly insufficient (e.g. Worksheet 2, questions 2 and 3); these answers were removed. Refer to your notes for justification of the answers.