Thursday, December 3, 2009

 

Thurs-Day 2


Bio 3/6 - we finished our discussion of the structure and function of the leaf, including the various layers and cell types. We focused on the guard cells that FORM the stoma/mouths/pores/stomates on the bottom side of the leaf. These stomates allow an easy entrance for CO2 gas from the air but they allow water vapor to escape.
We then discussed the transport of water in the xylem via capillary action, which is due to adhesion of water to the xylem walls and cohesion of water molecules to each other.
We reviewed how and why of the factors that influence the rate of photosynthesis and drew graphs of each factor as the independent variable. We even saw that color type could be used as an independent variable that influenced photosynthetic rate.
We then introduced the definition and equation for cellular respiration.


We used ORBITAL DIAGRAMS from the Quantum Model of the atom to explain ANOMALIES in the first IE trend. We invoked the concept of "shielding" WITHIN a principal energy level: the fact that "s" electrons are, on avg., closer to the nucleus than are "p" electrons so that the s electrons partially shield or BLOCK some of the positive nuclear charge from the p electrons thus making the p electrons easier to remove from the atom (lower than PREDICTED first IE!). we reviewed the first ionization anomalies among Group 3A elements and saw that the first IE value is LOWER than expected due to the shielding of the p electron by the two s electrons, making the p electron less attracted to the nucleus thus requiring LESS ENERGY for removal of said p electron.
We saw that Group 6A elements ALSO have anomalous/lower than expected first IE's BUT this is NOT due to s to p shielding; we drew the orbital diagrams to show that the electron pair repulsion, which is more significant between electrons in the same orbital/region of space due to their mutual proximity, causes one of those two electrons to be more easily removed from the atom.

We then explained the trend in SUCCESSIVE ionization energies to see that when the first NON-valence electron is removed, their is a DISPROPORTIONATE increase in ionization energy required. This is because NON-valence electrons are attracted to their nucleus by a much higher Zeff and these electrons are located closer to the nucleus (lower # OPEL's) than are valence electrons. Both of these factors cause greater nuclear to electron attraction.

We then defined "electron affinity" as the energy released when a gaseous atom GAINS an electron. This is measured via a laboratory procedure in which electrons are directed at a gaseous sample of atoms and the energy change is then measured. Atoms that have high EA (electron affinity) do so because of a relatively high Zeff, few OPEL's, AND not too much electron-electron repulsion as a result of gaining the new electron.

# posted by C @ 10:55 PM


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