Wolfram - 14-1-2006 at 06:35
If you look in a chemistry book the atomic mass of C is 12.0107. Now this is the avarage atomic mass of the normal mixture of isotopes in nature.
atomic mass of [12]C is by definition 12.000, but what would the atomic mass of [13]C alone and [14]C alone be?
Is it so easy so that they are 13.00000 and 14.00000? Do you have a link to the individual atomic mass of various isotopes?
Here is a nice page about isotopes http://en.wikipedia.org/wiki/Isotope_table_%28complete%29
Thank you for any help.
[Edited on 14-1-2006 by Wolfram]
[Edited on 14-1-2006 by Wolfram]
[Edited on 14-1-2006 by Wolfram]
[Edited on 14-1-2006 by Wolfram]
12AX7 - 14-1-2006 at 06:54
Atomic weight, not molecular weight. Talking pure carbon, molecular weight can be very large indeed for single crystal graphite or diamond. 
Neutrons and protons are about the same mass and electrons are negligible (about a thousandth) and since 12C is composed of 6 neutrons and protons, 13
and 14C should be pretty well what you suspect. But not exact, because 12C contains equal proportions of neutrons, protons and electrons. Higher
elements add neutrons, which are not exactly one atw.
Tim
Wolfram - 14-1-2006 at 07:59
Yes Atomic weight is correct ofcourse.
neutrino - 14-1-2006 at 09:24
When you're going to those precisions, mass loss due to nuclear binding energies also has a significant effect.
unionised - 14-1-2006 at 09:41
IIRC iodine is mono-isotopic and has mass 126.9045. Quite a bit lower than 127
Even fluorine (again, all 1 isotope; 19F) is 18.998403 so the binding energy is quite significant.
[Edited on 14-1-2006 by unionised]
Dr. Beaker - 16-1-2006 at 13:44
as I recall nuclear chemistry, every nuclous beyond some Fe isotop (in term of added nucleons) is endothermic in respect to the seperated protons and
neutrons. if that's true then the mass of the isotops of those heavy elements should have been greater then the sum of the masses of the individual
necleons...
x 1H + y n + E -----> heavy isotope
any ideas?
Quibbler - 17-1-2006 at 07:25
56Fe has the highest binding energy divided by the number of nucleons. Adding more nucleons increases the binding energy so elements beyond 56Fe are
still stable. Its just when it gets to the stage where losing a helium (alpha particle) is energetically sound that nuclei fall appart sponteneously.
I actually do a lot of magnetic resonance so some of the minor isotopes are much more important for example 13C, 15N, 17O and 33S.