aga
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Water Polarity
Please bear with if this is a Noob error.
The H2O molecule has 2 covalant bonds between the O and the two H.
The H's 1 electron sharing with the O's 6 electrons in the O's valance shell.
It still has not been properly explained (anywhere i have found) what the mechanism is that only allows X electrons in each shell.
Assuming that electron 'shells' are truly as understood, then each shell is described by an electron orbit a distance on N further away from the
nucleus than the next lowest shell (or the nucleus if it's shell 1).
To my simplistic vision, that means that the electron path around the Hydrogen atom is shorter than it is around the Oxygen atom, as it travels around
shell 1 when it orbits the Hydrogen atom, and shell 2 when it orbits the Oxygen atom.
Basically it's a longer distance, so it takes longer to go around the oxygen atom, so on balance the oxygen atom has the electron for a longer time,
delivering a slight -ve charge at the oxygen end, and consequently a slight +ve charge to the hydrogen end.
I cannot see a constant velocity of the electron working well, given the changes in radius, so likely that the electron accelerates as it leaves the
oxygen and slingshots around the hydrogen, which would further reduce the time spent there.
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DraconicAcid
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That's an interesting way of putting it, but I don't think it's correct.
The electron isn't a set distance from the nucleus; in fact, it doesn't even have a defined location at any given time, and is best thought of as
being spread out over a mathematically-defined volume of space called an orbital (there is one orbital in the first shell, four in the second, nine in
the third, and so on). Because of the way quantum numbers work, only two electrons can fit in any single orbital (which is why you can fit 2
electrons in the first shell, 8 in the second, and 18 in the third). The stability of an electron in an orbital will depend (mainly) on the size of
the orbital (i.e., which shell it's in), and the nuclear charge of the atom. The larger the orbital, the further away most of the electron is from
the nucleus, and the less stable it is. The greater the nuclear charge, the greater the attraction for the electron, and the more stable the electron
will be in that orbital. Since oxygen has a much greater nuclear charge than hydrogen (+8 instead of +1), the electron is happier in oxygen's second
shell than in hydrogen's first shell.
That's for the individual atoms. When you bond the two atoms together, you basically add the two atomic orbitals and mathemagically divide them by
two to get two molecular orbitals- one more stable than either atomic orbital (the bonding orbital) and one less stable than either (the antibonding
orbital). The electrons will go into the stable bonding orbital and leave the unstable antibonding orbital empty, which is a more stable set-up than
having an electron in each atomic orbital (thus the bond holding the atoms together). Now, because the atomic orbital of oxygen is more stable than
that or hydrogen , the bonding orbital will have most of the electron density close to oxygen- that's where the electron is happiest. So that's where
most of the electron density is, giving oxygen a partial negative charge.
Basically, you don't want to think of the electron as a little blue dot whizzing around the nucleus or nuclei, going faster or slower, or being in an
orbit. The electron is spread out over a volume- it's more like peanut butter spread out over a slice of toast- thicker in some areas, thinner in
others. You can't ask yourself, how fast are the peanuts travelling? Are they going faster over some parts of the toast rather than others?
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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Chemosynthesis
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I hope I don't regret posting, as I've avoided responding thusfar, but I would argue that one could say no one really knows if the electron
distribution is just a normalized probability density of where to find an unknown, but absolute location of an electron due to the hermitian operators
of the Heisenberg Uncertainty Principle, or if the actual electron is dispersed.
I wish I remembered more about Slater determinants and Eigenstates/vectors, but I distinctly remember philosophical differences in interpretations
such as the collapse of the wave function possibly being objectively deterministic (de Broglie) rather than the classically assumed stochastic
interpretation that caught on from Born.
I know when I was taught about LCAO and quantum numbers, the rules of QM were hammered as purely observational and inductive sans any reasoning about
why they are as they are. If an explanation were required, it was usually explained as an energy reduction scheme, like anisotropy.
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aga
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Many thanks : Both very interesting and enlightening comments.
Certainly worth me reading vastly more on the subject.
I guess that in the context of Chemistry, the observed phenomena are what count, rather then the actual physics behind what makes those phenomena
happen.
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Galinstan
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of coarse the physics behind these phenomana matters if we didn't understand the reason thing happened we wouldn't be doing good science, it's about
matching the physics of what should happen to what is observed and explaining why and how.
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IrC
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Quote: Originally posted by aga  | | I cannot see a constant velocity of the electron working well, given the changes in radius, so likely that the electron accelerates as it leaves the
oxygen and slingshots around the hydrogen, which would further reduce the time spent there. |
Work is done to accelerate the electron and energy is radiated as a result. Energy not confined to a quantum value (other than E=hF).
As a result all water vanishes, we fall to the ground as dust, as we realize we are in an 80's B SciFi movie: 'Night of the Comet'. Starring two great
looking ladies so maybe not so bad a fate after all.
So the question remains do we rethink your premise as we contemplate 'to be or not to be', or do we find a torrent for that movie as we have not seen
it in years?
"Science is the belief in the ignorance of the experts" Richard Feynman
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blogfast25
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For a beginner it helps to consider only the outer orbital electrons as it is those who take part in chemical bonding. The inner electrons are so
tightly bound to the nucleus that, by and large, we don't have to consider them in chemistry.
This is one of the reasons why electron configurations in textbooks are often abbreviated as follows:
Na = [Ne] 3s<sup>1</sup>
..meaning that the electron configuration of sodium is that of Neon, plus one lone, outer 3s electron. The 'neon electrons' don't take part in
sodium's chemistry, only the lone 3s electron does. And it explains much of sodium (and other alkali metals) chemistry: the lone 3s electron is
relatively easy to rip off the atom, leaving a sodium ion, that is Na<sup>+</sup>, with the same electron configuration as the chemically
inert and stable neon.
Conversely, chlorine is Cl = [Ne] 3s<sup>2</sup>3p<sup>5</sup> and has a tendency to accept an electron, thus becoming
Cl<sup>-</sup> = [Ne] 3s<sup>2</sup>3p<sup>6</sup> or... argon but with an extra electron:
Cl<sup>-</sup>. The other halogens behave very similarly.
Combine Na<sup>+</sup> and Cl<sup>-</sup> and you get strong mutual electrostatic attraction, resulting in a stable lattice
with both types of ions at alternating places in this three dimensional crystal. NaCl = kitchen salt.
Over-simplified this forms the basis of one very important type of chemical bonds: ionic bonds.
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blogfast25
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| Quote: Originally posted by DraconicAcid |
Basically, you don't want to think of the electron as a little blue dot whizzing around the nucleus or nuclei, going faster or slower, or being in an
orbit. The electron is spread out over a volume- it's more like peanut butter spread out over a slice of toast- thicker in some areas, thinner in
others. You can't ask yourself, how fast are the peanuts travelling? Are they going faster over some parts of the toast rather than others?
|
Electrons in much simpler situations (like one, two or three dimensional square or rectangular boxes) behave like standing waves, with discrete,
quantised energy levels. That was also the basis of Schrodinger's heuristic derivation (for mono-electronic atoms).
A lone electron, bound by a central electrostatic field (the nucleus of the atom), is thus expected to behave as a three dimensional standing wave.
This is seriously beyond imagination (except perhaps for the radially symmetric s orbitals) and it's best, I think, to simply accept the mathematical
description of electrons, rather than to try and imagine what a real atom's electron orbitals must 'look' like.
Who was it that said [or words to that effect]: 'If you think you've understood quantum mechanics, you've probably not studied it enough!'
[Edited on 4-4-2014 by blogfast25]
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aga
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From a practical standpoint, I totally agree : that's is all that needs to be known.
Having said that, i really would like to get up to speed with where current knowledge is at.
A particle behaving as a wave seems pretty straightforwards to me, as does said particle (or wave) even existing or not at any given point in the
dimensional framework.
Imagining the usual 4 dimensional reality is fine. 6 dimensions and beyond makes my head hurt, but that's where maths takes over.
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blogfast25
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When trying to teach people about atoms, I like to use the 'particle in a box' model, because as a simple quantum system it displays much of the
characteristics of more complicated systems, like quantisation, ground state energy > 0, orthogonality:
http://en.wikipedia.org/wiki/Particle_in_a_box
Here are some musings of mine about a one-dimensional hydrogen 'atom':
http://www.sciencemadness.org/talk/viewthread.php?tid=16001&...
Interestingly, the one-dimensional system only shows 's-type orbitals'.
[Edited on 7-4-2014 by blogfast25]
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aga
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α1 = ½ (2π e2m/hε0)3/2
hmm. need to have a think about that one.
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aga
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OK.
I had to go look up 'permittivity' as i'd forgotten what it was (resistance to EM propagation).
First stab : looks like you're calculating the energy of a thing based on it's 'distance' from a zero-point along what is assumed to be a
one-dimentional sinusoidal wave, so distance could be 'phase', or maybe angular position..
Still no idea what 'normalisation' is, or even what 'wave function' really means here.
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blogfast25
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Essentially the equation is the time independent version of the Schrodinger Equation but applied specifically to this system.
The equation is no more than an energy conservation balance. For a given energy level, say E, the electron possesses both kinetic energy (of the
wave), E<sub>kin</sub>, and potential energy, E<sub>pot</sub> (which is the result of the electrostatic attraction between the
nucleus and the electron). Energy conservation dictates that at all times E = E<sub>kin</sub> + E<sub>pot</sub>. By developing
this argument, expressions for E and the amplitude of the wave function can be found.
By wave function (in my piece notated as y, but usually as Ψ ) has to be understood the amplitude of the wave in function of the distance (so,
Ψ(x)). In quantum mechanics, the square of Ψ, i.e. Ψ<sup>2</sup> represents the probability that the electron will be found
there.
Normalisation is the result of integration of this second order differential equation: in essence it places limits on how far the electron can stray
from the nucleus.
[Edited on 7-4-2014 by blogfast25]
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aga
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i know it's off-topic, but i'm really pleased to meet someone with schooling in quantum physics.
If i say anything demonstrably wrong, please jump on it and flatten it.
How i imagine an entity, irrespective of size, is as a manifestation of a great multitude of things coming together and co-inciding at a point where i
observe it, from which i can try to deduce things about it.
Applied to the nature of electrons, i see an electron as a manifestation of an n-dimensional entity.
That is, each 'property' it has exists as a dimension. e.g. height, length, breadth, spin velocity, mass, when, gravitiation, magnetism etc - a
simple extrapolation of the dimensions we 'know'.
It flies about (maybe randomly, maybe oscillating) not only in the 'where', but also in all other dimensions as well.
So, at a point where it does not 'exist' in a specified space and time, it is simply not manifesting it's energy in the dimensions of x,y,z and When -
it is co-ordinated elsewhere, or elsewhen, or elsemass.
It could be that it's perceived energy is the sum of it's 'measurements' in all the dimensions that it occupies.
Fits OK with my understanding of Uncertainty, in that an entities position may well be calculated correctly, just totally out of phase in the Time, or
any other, dimension.
Energy conversion/release also works nicely : the poor thing lost something in the length, spin and popularity dimensions to make that wave.
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aga
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Cool !
This works better than the Many Worlds idea, and Schrodinger's cat was alive when all it's bits' dimensions aligned in one configuration, but was dead
in another configuration.
All the bits' dimensional presences align differently again, and it will have been born this time next Tuesday.
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Dan Vizine
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"Who was it that said [or words to that effect]: 'If you think you've understood quantum mechanics, you've probably not studied it enough!
--Blogfast
Soooo true. In fact, our view of the world around us is colored very strongly by the extremely narrow band of inputs our senses perceive, the snail's
pace of our fastest movements, etc.
You'd never dream, based on daily observations, that you weigh more as your velocity increases, that you shorten in the direction of movement, that
time slows down (technically that's true for acceleration only, there's no such thing as "absolute velocity" because...well, compared to what frame of
reference? Absolute acceleration exists, however.) but these happen always. "True" descriptions of objective reality are monsterously complicated.
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aga
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Imagine this.
Dimensions :-
X
Y
Z
Time
Magnetic
Electric
Gravitational
Van der Vaalian etc etc etc (basically all the Unknown Others, maybe infinite)
All intersect. Point of intersection of each dimension variable.
Energy=Sum of the expression of the Intensity of the imbalance of the intersection points, maybe plus some unknown 'pressure' exerted by the Extent of
the movement of said point in each dimension.
Equilibrium *might* what the system wants, but it's all wobbly, but it might want that instead.
The Big Bang was just the oscillations going crazy.
As the dimensional variances proceed, interact, oscillate ... all matter is expressed by this 1, singular 'entity' expressing itself (co-ordinating)
in many and varied ways.
Time isn't important in isolation - it's simply one of the variables, all of which are varying.
Hence Speed, frequency etc are also just expressions of the phenomenon, but isolated to 4 of the possibly infinite interacting dimensions involved.
Uncertainty is possibly an observation that a particle simply is not expressed in a particular reality (i.e. the one we want it to) at the Time
expected : it is expressed elsewhere, but will certainly be expressed 'here' at some time.
Obviously i'm no quantum mechanic, but it is clear to me that Time is VITALLY important when applied to 'What Time Does the Beer Shop Close'.
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aga
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I would argue that there is no 'True'.
Rather: 'This seems to work OK for now'.
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Chemosynthesis
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| Quote: Originally posted by blogfast25 |
Who was it that said [or words to that effect]: 'If you think you've understood quantum mechanics, you've probably not studied it enough!'
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Sounds like a Bohr quote. He also was known for saying "your theory is crazy, but not crazy enough to be true."
A favorite Dirac quote of my teacher's was always "shut up and calculate."
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