Monday, December 8, 2008
Mon-Day 1
AP Chem- we drew several Lewis structures involving resonance structures. ONLY the double bond or triple bond locations vary among resonance structures, NEVER the placement of atoms.
We discussed the relative lengths and strengths of single, double, and triple bonds seeing that the greater the number/order of the bond, the greater its strength and the SHORTER its length because, when there are more pairs of shared electrons between TWO positive nuclei, there is BY FAR much more net attraction.
We saw that actual bond order of a molecule that has resonance structures is a weighted average of all of its resonance structures i.e. the average bond order in nitrate ion is 4/3 because there are 4 pairs of electrons shared among 3 pairs of positive nuclei. A 4/3 bond is stronger and shorter than a single bond but weaker and longer than a double bond.
We discussed the "game" of formal charge, which is in no way, shape, or form real Coulombic charge. It is just a game invented by some chemists (and the game usually "works") to help decide the more and the less significant resonance structures in molecules that have several possible resonance structures.
We learned the Kaplan shortcut (saves SO much time and annoyance) for getting the formal charge of an atom in a resonance structure simply by drawing a circle around the atom and halfway through any bonds that it forms.
We applied the formal charge game and , most importantly, used it with REAL spectroscopic data to rationalize the best Lewis structure according to bond length and bond order.
We discussed our precipitation lab a bit more... we will continue that by writing out the net ionic equations that occurred during the analytical procedure.
Bio 6-8: we had the Cellular Respiration, Photosynthesis, and Plant Structures exam. Those who carefully followed the test-taking/test skills advice scored big-time again. Those who continue to not bother with these simple techniques lost many points due to careless errors and answered questions that were not there or used pronouns that referred to nothing or wrote incorrect information where a labelled picture would have sufficed.
We discussed the relative lengths and strengths of single, double, and triple bonds seeing that the greater the number/order of the bond, the greater its strength and the SHORTER its length because, when there are more pairs of shared electrons between TWO positive nuclei, there is BY FAR much more net attraction.
We saw that actual bond order of a molecule that has resonance structures is a weighted average of all of its resonance structures i.e. the average bond order in nitrate ion is 4/3 because there are 4 pairs of electrons shared among 3 pairs of positive nuclei. A 4/3 bond is stronger and shorter than a single bond but weaker and longer than a double bond.
We discussed the "game" of formal charge, which is in no way, shape, or form real Coulombic charge. It is just a game invented by some chemists (and the game usually "works") to help decide the more and the less significant resonance structures in molecules that have several possible resonance structures.
We learned the Kaplan shortcut (saves SO much time and annoyance) for getting the formal charge of an atom in a resonance structure simply by drawing a circle around the atom and halfway through any bonds that it forms.
We applied the formal charge game and , most importantly, used it with REAL spectroscopic data to rationalize the best Lewis structure according to bond length and bond order.
We discussed our precipitation lab a bit more... we will continue that by writing out the net ionic equations that occurred during the analytical procedure.
Bio 6-8: we had the Cellular Respiration, Photosynthesis, and Plant Structures exam. Those who carefully followed the test-taking/test skills advice scored big-time again. Those who continue to not bother with these simple techniques lost many points due to careless errors and answered questions that were not there or used pronouns that referred to nothing or wrote incorrect information where a labelled picture would have sufficed.
# posted by C @ 4:46 PM 
