OK, the return of the first exam was today, with a brief run-through to show where most of the problems seemed to occur. Check the key, come to me with questions if necessary. If you suddenly find that you are not performing up to your standards/expectations, you need to make sure that you are getting help -- either me, the group study sessions, or a tutor.
Today we started looking at Chapter 5, which deals with reactions. The main point was to show that we can look at reactive processes using the same methods as we used for resonance structures and acid/base reactions -- curved arrows, indicating electron movement.
We saw two kinds of electron movement in bond cleavages -- homolytic (both sides of a bond are treated the same way and each atom receives an electron; use "fish hook" arrows) and heterolytic (the sides are treated differently and one atom receives both electrons and the other is given none). The direction that the electrons flow in a heterolytic cleavage is governed by the polarity of the bond -- the electrons flow in the direction of the atom that is happier to have excess electrons. Generically, this is decided by electronegativity. The concept is made a bit simpler by the realization that nearly all heteroatoms (anything other than a C or H) attached to a carbon is more electronegative than the carbon and will grab the electrons from a carbon-heteroatom bond, leaving C with only six electrons and a more positive charge.
The picture is of a "rotating bomb combustion calorimeter," an instrument used to measure the energy contained within a compound. In this particular picture, it is being used to measure the differences between fuel oils containing differing amounts of heteroatom additives.
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