Monday, December 11, 2006
Monday
AP: we further developed our all-encompassing chart with AX2E, AX4, AX3E, AX2E2, and AX5 structures. If you study the posted videos and look at the "floating" molecules that have always been just below the "Files" section of the class website, you will become familiar with all of these minimum repulsion electron geometries and the bond angles that result from the symmetric geometric distribution of electrons. Only the AX5 electron geometries result in two different bond angles. We will do more of those tomorrow.
Once the whole chart is done, we will do some more examples to make sure that everyone is solid gold on this ridiculously important and fun topic.
Honors: We determined how to tell from a chemical formula whether a compound is an ionically bonded salt or a covalently bonded molecule. We then focused on ionic bonding throughout a crystal lattice. In any salt lattice, each cation is completely surrounded by anions and vice versa BUT the ratio of cations to anions in the lattice overall is determined by the charges of the cations and anions. We showed how to determine the formula for any binary salt that contains the cations of a representative metal and anions of any nonmetal. We then showed the mechanism of electron transfer that would lead to the formation of the ions in the salt, which then ionically bond to each other due to the attractions of the oppositely charged ions. This bonding is tremendously potential energy lowering and, thus, stabilizing; that is why salts naturally form from metals and nonmetals and the process is quite exothermic. Tomorrow, we will continue with salt formulas and then we shall discuss covalent bonding (nonmetal to nonmetal!) in individual molecules.
Regents: we took our brief quiz and then we got into drawing Lewis Dot structures of molecules. There are four to five rules and they must be strictly obeyed IN ORDER, otherwise your structure will be flawed.
I finished grading the quiz from today. Some of you are still having trouble with this material yet extra help is a ghost town except for the students who are doing well who come to extra help (what a coincidence). If you are doing poorly and you can't/won't come to extra help, you're going to have to get a tutor NOW. This topic is never going to go away; it is intrinsic to the rest of the course.
Here are some of the problems that I witnessed from grading the quiz today:
1. Some students are using TWO CAPITAL LETTERS FOR ONE ELEMENT! This is UNBELIEVABLE! NOT ONLY have I NEVER drawn two capital letters for a single element, but also the Periodic Table CLEARLY shows the symbol for each element. For example, sodium (natrium) is Na, NOT NA !!!!!! Notice, EVERY SYMBOL THAT CONTAINS TWO LETTERS has ONLY THE FIRST LETTER IS CAPITALIZED! Do not "do your own thing" in chemistry. There are rules and conventions and, if you break them, then you are WRONG and you will NOT get credit. Chemistry rules are NOT ARBITRARY, they are VERY important. The rules were made to prevent ambiguity, confusion, and dangerous miscommunication.
Clearly, those who are making this error cannot be doing the homework or taking notes in class.
2. Reminder: you shouldn't need this crutch by now, however, the NAME and matching SYMBOL of EVERY ELEMENT ON THE PERIODIC TABLE is on reference table "S" !!! WHY did half of you use "B" for bromide??? Bromide is the anion of Bromine, which is Br, directly on Table S !!! "B" is Boron!
3. DO NOT DEVIATE IN ANY WAY, SHAPE, OR FORM from the polyatomic ions listed in Reference Table E!!! More than half of you wrote phosphate as Po4 3- instead of the WAY IT IS WRITTEN FOR YOU DIRECTLY IN THE TABLES; go check.
"Po" means Polonium, as you may have heard about in the news recently involving the killing of the Russian dissident.
The same goes for sulfate, which is NOT So4 2-; see and write the ion EXACTLY as it appears in Table E.
4. Here's a general EXTREMELY IMPORTANT TEST TAKING TIP, especially when the tests actually determine your average in the course: WRITE CLEARLY AND CAREFULLY!!! Test and quizzes are the main opportunity to show that you actually know the material.
Why did some students draw ALL FOUR LEWIS STRUCTURES in such a small space that the STRUCTURES OVERLAPPED??!!! That is absolutely unbelievable to me. I can't tell which electrons belong to which element!!! You therefore GET NOTHING. If you want credit, do not ever cram any answers together on any test.
You only had to take care and put more than ONE millimeter between your answers, not leave three quarters of the page BLANK! This is not a test of how much info that you can cram into a small space!
Follow the above advice TO THE LETTER on all upcoming tests and quizzes.
Once the whole chart is done, we will do some more examples to make sure that everyone is solid gold on this ridiculously important and fun topic.
Honors: We determined how to tell from a chemical formula whether a compound is an ionically bonded salt or a covalently bonded molecule. We then focused on ionic bonding throughout a crystal lattice. In any salt lattice, each cation is completely surrounded by anions and vice versa BUT the ratio of cations to anions in the lattice overall is determined by the charges of the cations and anions. We showed how to determine the formula for any binary salt that contains the cations of a representative metal and anions of any nonmetal. We then showed the mechanism of electron transfer that would lead to the formation of the ions in the salt, which then ionically bond to each other due to the attractions of the oppositely charged ions. This bonding is tremendously potential energy lowering and, thus, stabilizing; that is why salts naturally form from metals and nonmetals and the process is quite exothermic. Tomorrow, we will continue with salt formulas and then we shall discuss covalent bonding (nonmetal to nonmetal!) in individual molecules.
Regents: we took our brief quiz and then we got into drawing Lewis Dot structures of molecules. There are four to five rules and they must be strictly obeyed IN ORDER, otherwise your structure will be flawed.
I finished grading the quiz from today. Some of you are still having trouble with this material yet extra help is a ghost town except for the students who are doing well who come to extra help (what a coincidence). If you are doing poorly and you can't/won't come to extra help, you're going to have to get a tutor NOW. This topic is never going to go away; it is intrinsic to the rest of the course.
Here are some of the problems that I witnessed from grading the quiz today:
1. Some students are using TWO CAPITAL LETTERS FOR ONE ELEMENT! This is UNBELIEVABLE! NOT ONLY have I NEVER drawn two capital letters for a single element, but also the Periodic Table CLEARLY shows the symbol for each element. For example, sodium (natrium) is Na, NOT NA !!!!!! Notice, EVERY SYMBOL THAT CONTAINS TWO LETTERS has ONLY THE FIRST LETTER IS CAPITALIZED! Do not "do your own thing" in chemistry. There are rules and conventions and, if you break them, then you are WRONG and you will NOT get credit. Chemistry rules are NOT ARBITRARY, they are VERY important. The rules were made to prevent ambiguity, confusion, and dangerous miscommunication.
Clearly, those who are making this error cannot be doing the homework or taking notes in class.
2. Reminder: you shouldn't need this crutch by now, however, the NAME and matching SYMBOL of EVERY ELEMENT ON THE PERIODIC TABLE is on reference table "S" !!! WHY did half of you use "B" for bromide??? Bromide is the anion of Bromine, which is Br, directly on Table S !!! "B" is Boron!
3. DO NOT DEVIATE IN ANY WAY, SHAPE, OR FORM from the polyatomic ions listed in Reference Table E!!! More than half of you wrote phosphate as Po4 3- instead of the WAY IT IS WRITTEN FOR YOU DIRECTLY IN THE TABLES; go check.
"Po" means Polonium, as you may have heard about in the news recently involving the killing of the Russian dissident.
The same goes for sulfate, which is NOT So4 2-; see and write the ion EXACTLY as it appears in Table E.
4. Here's a general EXTREMELY IMPORTANT TEST TAKING TIP, especially when the tests actually determine your average in the course: WRITE CLEARLY AND CAREFULLY!!! Test and quizzes are the main opportunity to show that you actually know the material.
Why did some students draw ALL FOUR LEWIS STRUCTURES in such a small space that the STRUCTURES OVERLAPPED??!!! That is absolutely unbelievable to me. I can't tell which electrons belong to which element!!! You therefore GET NOTHING. If you want credit, do not ever cram any answers together on any test.
You only had to take care and put more than ONE millimeter between your answers, not leave three quarters of the page BLANK! This is not a test of how much info that you can cram into a small space!
Follow the above advice TO THE LETTER on all upcoming tests and quizzes.
# posted by C @ 6:29 PM 
