Wednesday, January 17, 2007
Wednesday, Day 4
Honors: MULTIPLE CHOICE bonding unit test tomorrow, which will cover the unit on bonding, naming, and attractions up to and including "induced dipole' attractions that we covered in class today.
This correction came up at extra help:
on the file from 011407 entitled "Chemical Bonding Worksheets and Practice Tests", on the Bonding I Self Test,
Question #1 has two correct answers: during ion formation, the atom that TRANSFERS (loses) its valence electron(s) is the (metal atom) one with the LOWER electronegativity OR the LOWER ionization energy; both of those answers (B) and (C) are correct! To see this, just think of sodium chloride formation.
Question #20 is NOT written correctly; it SHOULD read, "ALL COVALENT chemical bonds are the result of ..."
the correct answer is then (D), "simultaneous attraction of electrons to two nuclei"; as an example, think of the covalent bond in an H2 molecule or in a CH4 molecule.
Today we reviewed ion-dipole attractions and their relationship to the solubility of salts. We then discussed ion-induced dipole attractions between a salt and a nonpolar solvent: these attractions are not strong enough to overcome ionic bonds, therefore salts are not soluble in nonpolar solvents.
We then explained the process of induced dipole formation as the source of attraction between/among nonpolar molecules. The more polarizable the molecule, due to a greater number of total electrons per molecule, the stronger and more frequent the induced dipoles and therefore, the greater the induced dipole attractions, which are sometimes called "London dispersion" or "Van der Waal's" attractions.
Regents: we reviewed parts of our last test and found a few more points for the class, good times. We then explained ion-dipole attractions and their relationship to the solubility of salts. When there are enough ion-dipole attractions between an ion and its surrounding polar solvent molecules, then the NET force of attraction between these particles may be sufficient to break the ionic bond between the ion and surrounding oppositely charged ions so that the ion (salt) will dissolve/be solvated/be hydrated.
AP: today, we reviewed the various graphs that yield 0th, 1st, 2nd, and 3rd order rate constants and the units of each.
Then we explained , statistically, how the exponent of a rate law MUST match the molecularity of the elementary step.
We then showed that the SLOW step of a reaction is the "rate determining step".
We stated the criteria for a PLAUSIBLE proposed reaction mechanism: how the rate determining step of the proposed mechanism MUST agree with the EXPERIMENTALLY DETERMINED rate law ( there is NO OTHER WAY to get a rate law for a reaction!). Also, the sum of the mechanism steps must yield the overall balance equation.
We finished by showing how some mechanisms can agree with or not concur with an experimentally determined rate law. We will do more of these problems tomorrow.
This correction came up at extra help:
on the file from 011407 entitled "Chemical Bonding Worksheets and Practice Tests", on the Bonding I Self Test,
Question #1 has two correct answers: during ion formation, the atom that TRANSFERS (loses) its valence electron(s) is the (metal atom) one with the LOWER electronegativity OR the LOWER ionization energy; both of those answers (B) and (C) are correct! To see this, just think of sodium chloride formation.
Question #20 is NOT written correctly; it SHOULD read, "ALL COVALENT chemical bonds are the result of ..."
the correct answer is then (D), "simultaneous attraction of electrons to two nuclei"; as an example, think of the covalent bond in an H2 molecule or in a CH4 molecule.
Today we reviewed ion-dipole attractions and their relationship to the solubility of salts. We then discussed ion-induced dipole attractions between a salt and a nonpolar solvent: these attractions are not strong enough to overcome ionic bonds, therefore salts are not soluble in nonpolar solvents.
We then explained the process of induced dipole formation as the source of attraction between/among nonpolar molecules. The more polarizable the molecule, due to a greater number of total electrons per molecule, the stronger and more frequent the induced dipoles and therefore, the greater the induced dipole attractions, which are sometimes called "London dispersion" or "Van der Waal's" attractions.
Regents: we reviewed parts of our last test and found a few more points for the class, good times. We then explained ion-dipole attractions and their relationship to the solubility of salts. When there are enough ion-dipole attractions between an ion and its surrounding polar solvent molecules, then the NET force of attraction between these particles may be sufficient to break the ionic bond between the ion and surrounding oppositely charged ions so that the ion (salt) will dissolve/be solvated/be hydrated.
AP: today, we reviewed the various graphs that yield 0th, 1st, 2nd, and 3rd order rate constants and the units of each.
Then we explained , statistically, how the exponent of a rate law MUST match the molecularity of the elementary step.
We then showed that the SLOW step of a reaction is the "rate determining step".
We stated the criteria for a PLAUSIBLE proposed reaction mechanism: how the rate determining step of the proposed mechanism MUST agree with the EXPERIMENTALLY DETERMINED rate law ( there is NO OTHER WAY to get a rate law for a reaction!). Also, the sum of the mechanism steps must yield the overall balance equation.
We finished by showing how some mechanisms can agree with or not concur with an experimentally determined rate law. We will do more of these problems tomorrow.
# posted by C @ 12:34 PM 
