Chemistry 101

[bjjones37]

Okay, now you guys got me back into it, you have to put up with me pestering you with questions.  I am going back through my college textbook so that is the source for everything I am asking about.

The 'spin' of an electron within an orbital.  How can it have a direction if it motion is random within the orbital?  Or is it's motion random?  It says that the electrons must spin in opposite directions, but then says that this is mainly an analogy.  Is there a better description of it yet?  

Also the book describes and illustrates the shape of the electronic orbitals, but does not explain how they were derived. You know - s, p, d, and f.  How do we know their shapes?

[bjjones37]

Karlos wrote:

Now, you may (or may not) know that the probability of finding the electon at a specific point in 3D space is proportional to the square of the wavefunction at that point.

Once you know this, you can derive the "shape" of the obitals by defining a boundary surface that represents eg a 95% probability volume for the electron. That is to say there is a 95% chance the electron is somewhere inside that volume.

Any chance you could demonstrate the math used to derive, say, a p orbital? I don't really know what the wave function would look like. I assume these are standard equations derived for each of the orbitals to define their statistical boundaries.

[bjjones37]

Karlos wrote:
Off the top of my head, no chance :-D

An s orbital, would me more managable...

Hey, I could have asked for an f orbital.:-D

The wavefunction for the orbital where quantum n=1 (corresponding to a 1s orbital) looks like

Phi = (1/(pi.a0^3))^(1/2) . e^(-r/a0)

where a0 is the Bohr radius and r the radial distance (This is for the 1s case only - for 2s etc you have to factor in the effect of increasing nuclear charge Z, and but the symmetry of the function doesn't change).

Could you clarify a0 (Bohr radius) and r (radial distance), using the nucleus as a frame of reference?

Would not the effect of the nuclear charge Z be reducing with each increase of n, or is this assuming a larger number of nucleons in a stable atom?

[bjjones37]

I know this may be one of those "just the way it is" things, but I would like a little insight on something. I was taught that covalent bonds are formed because elements like to have their valence shells filled - 1s, 2s, 2p and so forth.  At least this was the rationale I was given.  I don't remember any particular rational given for ionic bonding.  Some elements are more likely to form ionic bonds, others covalent bonds, and some do both. Calcium, which has it's valence shells filled up thru 4s is extremely reactive, while Gold which has an available 6s electron is rather nonreactive.  (This observation seems to be rather consistent for the IIA and IB elemental groups.)  Could you comment on why this is so?

[bjjones37]

bloodline wrote:
VSEPR theoy is just a "rule of thumb", it breaks down after atomic number 20 or there abouts.

The funny thing is that I could never work with VSEPR but had no problems with MO, for most people it's the other way around!

Could you clarify VSEPR and MO please? Not sure what the letters stand for.

[bjjones37]

More questions later, but for now I wish y'all to know that I am printing these responses and saving them for future reference.  It helps to fill in some of the gaps in my Chemistry text. And for past and future responses, my sincere thanks.  I have always loved Chemistry and have always regretted the necessity of giving it up as a major.  I did well in the two years of General and Organic Chemistry I had in college and after reviewing them, I hope to move on to the texts in Physical, Quantum, and Biochemistry which I have acquired.  May not be able to do any lab work, but at least I can acquire the principles. Perhaps when I retire I can go back to college.  The University I have available only offers Upper division chemistry classes in the morning, and I must work as I provide the sole income for my family. I have great hopes to complete my Chemistry degree when I retire, but I do not wish to wait that long to learn more about it.

[bjjones37]

This Chemistry review came just in time.  My children are doing Chemistry in high school now and it is up to Daddy to help themm out.  Thanks guys. :-)