Re: how is it that the Atomic Mass Unit is less than either the
- From: Sean Case <seancase@xxxxxxxxxx>
- Date: Wed, 20 Sep 2006 09:29:55 +0000 (UTC)
In article <C1322FB8.1A7E%rbj@xxxxxxxxxxxxxxxxxxxx>,
robert bristow-johnson <rbj@xxxxxxxxxxxxxxxxxxxx> wrote:
even if the electrons weighed nothing, each proton and neutron is more
than the amu so it must add to more than 12 amu. how can this be?? i
know that this is a definition, but it seems to me that the definition
does not square with CODATA values of the most massive components of a
carbon-12 atom and the conservation of mass principle. how does
sticking these 6 neutrons and 6 protons together, toss in 6 electrons
and maybe some binding energy/c^2 add up to less than the total? i
don't get it.
The binding energy is negative. That is, when you take six neutrons
and six protons and squeeze them into a carbon nucleus, more energy
comes out than you used up in the squeezing. And when you throw some
electrons at the nucleus to make a neutral atom, they radiate away
some energy as they fall into place. This means you have to subtract,
not add, some energy to get the total mass of the atom.
If the total energy of a bound carbon atom weren't less than the sum
of its parts, of course, carbon atoms would tend to fall apart, which
would be bad luck for any life-forms based on carbon chemistry.
Sean Case
.
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