[geocentrism] Re: Atoms & Electrons

  • From: Regner Trampedach <art@xxxxxxxxxxxxxx>
  • To: geocentrism@xxxxxxxxxxxxx
  • Date: Mon, 11 Feb 2008 15:14:50 +1100

Philip
  First of all, you seem to confuse atomic and nuclear physics - there is a large gap of a
factor of 100 in energy between the two disciplines!  I know the media often call it
"atomic energy" and "atomic bomb" when it is nuclear, but I thought an engineer would
know the difference.
   Basic structure of atom:
      Small nucleus:  Diameter about 1.6-15 fm (1 fm = 10^(-15) m = a thousandth of a
            millionth of a millionth of a meter = 0.[14 zeroes]1 m).
            The nucleus consists of protons and neutrons.
            Protons have a positive electric charge and the number of protons determines
            which element the atoms is of, e.g., 8 protons for oxygen, 26 for iron, 82 for
            lead, etc. Have a look at a periodic system.
            The number of neutrons determines the isotope of a given element.
            The most common isotopes have equal numbers of neutrons and protons for
            elements lighter than calcium (Ca, N=20) and more neutrons than that for
            heavier elements.
            Neutrons have no electric charge, but have nearly the same mass as protons.
            Since there are no negative charges in the nucleus, the nucleus would explode
            in  nanosecond if there wasn't something else to keep the protons together.
            That something else is "The strong nuclear force" - one of the four fundamental
            forces in nature. Unlike gravity and the electric force, the strong nuclear force is
            limited in range (doesn't reach to infinity) and only reaches about 1.3 fm. So this
            force only attracts neighbouring protons and neutrons and doesn't span the whole
            nucleus. The force is also repulsive at shorter distances, which means the
            separation between protons and neutrons in a nucleus is almost constant irrespective
            of element and isotope.
            The strong nuclear force only acts on hadrons - neutrons and protons are hadrons,
            but electrons are not.
       "Cloud" of electrons: Electrons are almost 2000 times lighter than protons and neutrons
            therefore containing only 1/4000th of the mass of the atom.
            Electrons have a negative electric charge, exactly canceling that of a proton.
            The electron cloud is about 100,000 times larger than the nucleus - scaled up (a bit!)
            that means that if the nucleus was the size of a fly, the electron cloud (and therefore
            the atom) would be the size of one of the larger Cathedrals of the world. It is fair to
            say that atoms consists of mainly nothing.
            In a neutral atom, the number of electrons balance the number of protons in the nucleus.
            In positive ions you have fewer electrons, and some elements can even have stable
            negative ions, with an extra electron.
               One major consequence of quantum mechanics (and observed property of the
            atomic world), is that these particles are not infinitely small points, but rather smeared
            out in space according to Heisenberg's uncertainty principle. It is a probability
            distribution of finding the electron in a particular point in space - called the wave-
            function (since it obeys much of classic wave-mechanics). This is the reason electrons
            form a cloud around the nucleus, instead of orbits, Even though there is no
            way of telling exactly where a particular measurement will find an electron (only
            the probability of finding it in any particular spot) the wave-functions themselves,
            behave absolutely deterministically.
            The size is inversely proportional to mass, so the electrons have much larger wave-
            functions than the nucleus.
           
  Atomic physics as well as chemistry deals with the electron cloud only. Chemistry usually
keeps to temperatures below about 500 K, and atomic physics stays below about 100,000 K.
When you reach energies where nuclear reactions can take place, you are in the realm of
nuclear physics.

philip madsen wrote:
 
Modern physics doesn't seem to know
Well, I'm afraid we do.
and has a variety of models, with shells and other configurations or models.
What governs the structure of atoms is the Schrödinger equation of quantum mechanics
and the electric force. That is just as established as the fact that the Sun heats the Earth.
For hydrogen - a proton and an electron - you can solve the structure analytically, i.e.,
you can write down equations that give you the structure of the atom, exactly. That is
because it is a two-particle system. Have a look at
        http://en.wikipedia.org/wiki/Hydrogen_atom
for more details, and a "picture" of the electron orbitals of a hydrogen atoms can be found
here:
        http://en.wikipedia.org/wiki/Hydrogen_atom#Visualizing_the_hydrogen_electron_orbitals
The various orbitals correspond to various excited states - the atom has gotten some sort of
"kick" and is no longer in the ground-state. It will decay to the ground state (1s) by emitting
a photon with the energy-difference.
  For other atoms you need to solve the equations numerically - which means trying with a
first guess, from which you can calculate how to improve to get a better guess - you iterate
that process until you get the required accuracy. The measure of success is the total energy.
An equilibrium state has the lowest energy possible, so you basically scan parameter space
for a global minimum in energy. The problem is the dimension of this exercise:
  Each electron has a position (x-, y- and z-coordinate) and a velocity (vx, vy and vz) - so it
takes 6 parameters to describe each electron, which means you need to scan N*6 dimensional
space for an energy minimum for an atom with N electrons. That quickly gets far too huge
to do on todays super-computers. That means that atomic physicists need to be clever and
look for patterns that means the problem can be simplified. That pattern is the shell model:
  According to this model, each electron is described by three quantum numbers, n, l and m.
The principal quantum-number, n, is the number of the shell (1,2,3,...) and the radius and
energy of the orbital depends mainly on this number - higher n means higher r and E.
The angular quantum number, l=0,...,n-1, determines the shape of the orbital (l=0 means
round) and the magnetic quantum number, m=-l,...,0,...,+l, only perturbs the energy
modestly. Each (n,l,m) combo is an energy state and each energy-state can only harbour
up to two electrons (Pauli's exclusion principle). All in all, that means that each shell, n,
can harbour up to 2*n*n electrons = 2, 8, 18, 32, etc. for each shell.
  An electron fills up its shells from the inside (this results in the lowest total energy),
which means that neon (Ne, N=10) has the n=1 and the n=2 shells filled, and no extra
electrons - that means it is an inert gas. Chemistry and a lot of atomic physics is determined
by the number and configuration of the electrons in the outermost shell.
  The shell model is not an assumption. It falls out of the Schrödinger equation (and the
relativistic extension of it, which is called the Dirac equation) when combined with
the conservation of energy and angular momentum (basically rotation). And it has stood
up to nearly a century of experiments.
  To give you all a feeling for the state of atomic physics, I have reproduced Fig. 3, of
H Kjeldsen et al 2002 J. Phys. B: At. Mol. Opt. Phys. 35 3655-3668.
Light absorption by iron ion.
 This figure shows how an iron ion, missing one electron, absorbs photons (light) of various energies
(horizontal axis) to kick out one more electron. Observations at top, two independent (and relativistic)
calculations at the bottom. The calculations, don't match the observations perfectly, which means we
need more sophisticated calculations - but remember that this is a 25 electron system, and we therefore
have 150 independent coordinates - a 150 dimensional space in which to find a minimum! The agreement
with experiment is truly impressive, and my description of atomic physics above, barely scratches the
surface of what goes on in this figure. A semi-classical Bohr-model, would just result in a constant
value above a threshold around 20eV and zero below.
  Conclusion: We understand atomic physics, but the numerical implementation is still a work in
progress, depending on how accurate your results need to be - that describes pretty well a mature
science, in general.
do a google and you will get entirely convinced that the nuclear physicist is just as much a dreamer as the cosmological.
 
Its a frightening thing that when they tested the first bomb, they crossed their fingers.  Would it work?
They understood the nuclear physics very well. They didn't know how to calculate many of
the needed quantities from scratch, but they could measure them, so didn't need the calculations
to engineer a bomb. The improved understanding from knowing the underlying physics and being
able to calculate those quantities, was of course necessary to making the bombs yet worse.
  The thing that was the big unknown, was the hydrodynamics: How fast would the blast expand
and therefore decrease in density below the critical density - that is, how much of the bomb would
explode, before being scattered.
and or would it chain react and destroy the atmosphere of the world?
Physicists knew about cosmic rays back then - these particles bombard the Earth's atmosphere
with much higher energies than anything we can come up with - nothing happens...
Nuclear fusion (as in hydrogen bombs) are yet more sensitive to density than fission bombs
(uranium and plutonium) and there is no way you could sustain a fusion reaction in the
Earth's atmosphere - no way!
And fusion is not a chain-reaction, anyway...
Warnings were given that Atmospheric tests whith thermonuclear H2 run this grave risk, hence the ban on high altitude tests. It was not all about radiation pollution.
Sigh...
And H2 is molecular hydrogen. Thermonuclear means fusion due to high temperature - higher
than 10,000,000 K (~20,000,000 F) - you don't have molecules then. Molecules are irrelevant
at the energies/temperatures of nuclear physics. You don't even have any atomic hydrogen left
- only fully ionized hydrogen - that is protons. The H-bomb is not named for the particular form
of the fuel when it is "shipped", but for the "active ingredient" at the time of detonation.
That "active ingredient" is deuterium and tritium (heavy isotopes of H (hydrogen), with one and
two neutrons, respectively), produced from LiD (lithium + deuterium molecule) irradiated by high
intensity flux of neutrons from the trigger-(fission) explosion.

Sorry for this post being so long, but there were a lot of misconceptions to clear up.
I hope this helped...

        Regner

Philip
----- Original Message -----
From: Jack Lewis
Sent: Friday, February 08, 2008 12:34 AM
Subject: [geocentrism] Re: Atoms & Electrons

I also forgot to ask if there is any relationship between the number of protons, the number neutrons and the number of electrons?


Jack Lewis wrote:
Dear All,
I'm doing an illustration of an atom and I would like to know if the electrons all orbit the nucleus at the same distance or do they have different orbits?

Jack

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