D4RR3N
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atomic energy density of elements
I have a question regarding the energy density of elements.
E = mc2 therefore mass is energy. Mass divided by volume gives you the density and since mass is energy we can call it the energy density.
If it were possible to know the true radius of an atom of a particular element e.g. Aluminum then you could calculate the true volume of that atom.
Divide the mass by the volume would give you the energy density for the atom. Since every element has a different mass and volume then each element
has its own energy density which is unique to it.
My question is this, If I wanted to make a chart so that it would be possible to make a comparison of energy densitys (on an atomic level) for various
elements could I use standard density (g/cm3) chart or would the difference in the crystal structure of each element introduce errors, i.e. some
crystal structures may geometrically allow more atoms per unit area then others?
I’m trying to explain this but not sure I have done a good job of it, hope you understand what I’m getting at.
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woelen
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The concept of density is a macrophysical concept. Speaking of density on the basis of a single atom makes no sense. Whether it be mass density or
energy density does not matter. You simply have to take into account that there will be 'unused' space in a lattice.
Think of a packing of oranges. Oranges have a certain density (which will be close to 1 gram/ml, probably a little more), but this only makes sense
because we regard an orange as a macroscopic object. Now think of an orange as single atom, and each orange has a unit mass, called OR. What would be
the density of a single orange, expressed in OR? Rather useless, isn't it? Now suppose we have a very large truck, filled with oranges. Now we again
can speak of density. Determine the volume of the truck's container, which is completely filled with oranges. Count the number of oranges, and we have
a density, which is N/V [OR/m3], with V the volume, and N the number of oranges, each having a unit mass OR. We could have a density of e.g. 700
OR/m3. This analogy also nicely shows the effect of lattice. The density, expressed in OR/m3 always is less than the volume of one cubic meter,
divided by the volume of an orange. Oranges do not fill 100% of space. The same is true for atoms and molecules.
The analogy of oranges allows the concept of density to some extent (several thousands of oranges). The larger the number of objects involved, the
more the continuum approximation is valid. On a macroscopic level we really may disregard the discrete number of atoms, there are so many, that for
all practical situations, we may regard the density function as a real continuous function.
Density of packings of oranges only begin to make sense with volumes in the order of magnitude of cubic meters. Density of packings of atoms and
molecules already makes perfectly sense at microliter volumes or even less.
[Edited on 20-9-07 by woelen]
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franklyn
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Density indicated by the greek letter rho ( ρ ) is mass divided by volume.
water is taken to have the value of one and all other elements and substances
are some multiple of this. The crytal lattice and bond length of an element
determines much of the volume of that element. I have not seen any atomic
order determined by density , it's easy enough to list elements by density.
You can use the atomic radius and atomic weght to figure the density of
a single atom. This is only approximate since the outermost valence electrons
are constantly changing state. The notion of an atom as a sphere is only a
convenient fiction. Orbital theory shows that there is quite a varied structure.
http://micro.magnet.fsu.edu/electromag/java/atomicorbitals/i...
Mass is only convertable to energy completely if two equal amounts of matter
and antimatter interact regardless of density.
p = m /V , so m = pV
E = mc² , so m = E /c²
pV = E /c² , so E /p = Vc²
.
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Sauron
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The fellow's concept is naive. Is he going to compare nuclear radii, or atomic radii? Atomic radii include electron shells, but these are variable.
In nuclear terms, what is important is the binding energy.
And so I strongly recommend the excellent book, "The Curve of Binding Energy" to anyone interested in nuclear energy. Perhaps it can be found in
Amazon or Allbris.
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franklyn
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The curve of binding energy is process specific , limited to fusion
or fission , and a gross indicator of available latent enrgy from that
process. Fusion of heavy elements is endothermic as is fission of
light elements. Take an amount of lead which is essentially inert to
nuclear meddling , drop this onto a neutron star and you will obtain
a considerable bang.
.
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D4RR3N
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If we take the example of Graphite and Diamond, both are composed of carbon atoms yet the density of graphite is 2.23 g/cm3 whilst diamond has a
higher density at 3.52 g/cm3. We can only assume this is due to the crystal structure of diamond geometrically allowing more carbon atoms per unit
area then graphite dose.
I do realise that atoms are not spherical in reality and I also realise that much of an atom is composed of empty space. The outer orbit is in
continuous dynamic change so its not possible to give it an exact value but an outermost limit (radius) could be established?
I know such a chart dose not exist but was wondering what a chart arranged by energy density would look like.
Radius of atoms determined by covalent bonding of two atoms, dose covalent bonding always occur on the same electron orbit for all elements?
[Edited on 21-9-2007 by D4RR3N]
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not_important
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IF you are talking about energy in terms of total conversion of mass to energy, then you get this:
http://www.science.co.il/PTelements.asp?s=Density
http://environmentalchemistry.com/yogi/periodic/density.html
Physical form and allotropes of elements would need to be taken into account, but a decent handbook or interactive periodic table will give you that.
If you are talking about energy we know how to extract, or believe nature to do, then you need to look at molar volumn and nuclear binding energy
http://www.webelements.com/webelements/properties/text/image...
http://web.lemoyne.edu/~giunta/chm151L/plots1.gif
http://www.alaskajohn.com/physics/charts/binding_energy.jpg
http://crippen.nevada.edu/KJC/courses/CIT707/content/nuclear...
http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=n...
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12AX7
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Single ended (i.e., without antimatter), the best thing we know of to convert mass to energy is a black hole. The conversion is something like 10%,
IIRC.
I don't know of any crashed Romulan Birds of Prey, so you're pretty well SOL until NASA plans a mission to our galactic neighborhood's supermassive.
Tim
[Edited on 9-21-2007 by 12AX7]
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Jdurg
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| Quote: | Originally posted by franklyn
Density indicated by the greek letter rho ( ρ ) is mass divided by volume.
water is taken to have the value of one and all other elements and substances
are some multiple of this. |
Well, that's true and false. Density is indeed Mass divided by Volume, but water's density of approximately 1 was not arbitrarily assigned like the
values in the Centrigrade Temperature Scale were. The Density of water is approximately 1.0 because one mL of water is equal to one gram. 1 L of
water is equal to 1 Kg. There's nothing "assigned" about it. The density of ALL substances out there have been measured, or calculated when direct
measurements are not possible.
\"A real fart is beefy, has a density greater than or equal to the air surrounding it, consists of the unmistakable scent of broccoli, and usually
requires wiping afterwards.\"
http://maddox.xmission.com. |
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Ozone
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IIRC, E=MC^2 is absolute. That is, a single proton is the near equivalent of 938 MeV and the electron yields approximately 0.51 (an electron:positron
annihilation event yields 1.022 or 2X0.51 MeV, at roughly 180°).
That's pretty much it--"density" on quantum scale amounts to probability rather than absolute volume (see "Dell^2")...and, the more accurately you
know the velocity of a given particle, the less you can define about its location (although one would think that the differential volume would be
fixed), but then there is...
Duality. How much volume is "displaced" by a photon oscillating it's way along (at a rather expeditious velocity)?
In the conventional sense, one cubic cm of protons (or any other discrete particle) would have quite an enormous (and calculable) heft...or not,
considering uncertainty .
Cheers,
O3
[Edited on 21-9-2007 by Ozone]
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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DerAlte
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Density depends entirely on the units used - for instance water has a density of 1000 kg/m^2 on the MKS system, but at one temp only, that of maximum
density. c. 4C. Specific gravity is the density of a substance compared to that of water at 4C. Specific gravity depends on temperature, pressure.
What any of this has to do with inorganic chemistry or chemistry topic of general interst beats me. Sounds like very elementary physics...
Der Alte
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franklyn
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| Quote: | Originally posted by Jdurg
water's density of approximately 1 was not arbitrarily assigned like the values in
the Centrigrade Temperature Scale were. The Density of water is approximately
1.0 because one mL of water is equal to one gram. 1 L of water is equal to 1 Kg.
There's nothing "assigned" about it. |
Ooh Yeah !
http://en.wikipedia.org/wiki/Metric_system
Quote _
In the late 18th century, Louis XVI of France charged a group of savants to
develop a unified, natural and universal system of measurement to replace the
disparate systems then in use. This group, which included such notables as
Lavoisier, produced the metric system, fundamental base units.
These were derived from each other via the properties of natural objects,
mainly the Earth and water: 1 metre was originally defined as 1/40,000,000th
of the polar circumference of the Earth, 1 kilogram was originally defined as
the mass of 1 litre (or, equivalently, 1 dm³) of water at its melting point (this
definition was later revised to specify a temperature of 4 °C). The Celsius
temperature scale was derived from the properties of water, with 0 °C being
defined as its freezing point and 100 °C being defined as its boiling point under
a pressure of one standard atmosphere.
The metre was later redefined as the length of a particular bar of
platinum-iridium alloy; then in terms of the wavelength of light emitted by a
specified atomic transition; and now is defined as the distance travelled by
light in an absolute vacuum during 1/299,792,458 of a second. The gram,
originally one millionth of the mass of a cubic metre of water, is currently
defined by one thousandth of the mass of a specific object that is kept in a
vault in France; however there are efforts underway to redefine it in terms of
physical quantities that could be reproduced in any laboratory with suitable
equipment.
If that's not arbitrary I don't know what is.
" water is taken to have the value of one " I say nothing about it being an
arbitrarilly assigned reference for comparison. But since you brought it up ,
that is - exactly what it is.
A L L weights and measures are the concensus of some convenient
reference standard. The density of water is one because that I S
the chosen unit of measure derived from the meter - 1 liter / 1 kg. , 1/1 = 1 , one
not two or three or thirteen of something else.
It didn't just coincidentally happen to be one , it was chosen to be one.
http://en.wikipedia.org/wiki/Mensuration
.
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12AX7
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Planck units are perhaps the least arbitrary system, but the most commonly encountered values (such as those on the scales of eV, amu, kg, J, W, m and
so on) end up with extreme exponents that computationally aren't of any consequence, but make for very inconvienient use.
BTW, protons don't like to hang out together, but you could have a solid block of neutrons. It might be convienient to declare it as room
temperature. The deBroglie wavelength is pretty small (due to the large particle mass), so "neutronium" is quite dense. Since wavelength depends on
energy, and average energy depends on temperature, such a material might actually shrink on heating.
Tim
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