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Difference between revisions of "Atomic mass units"

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The Atomic Mass Unit is defined as the twelfth part
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The '''atomic mass unit''' (AMU) is defined as the twelfth part
 
of the mass of a C<math>_{12}</math> atom.
 
of the mass of a C<math>_{12}</math> atom.
 
Its value (in SI units,
 
Its value (in SI units,
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Hence,
 
Hence,
 
it is approximately equal to the mass of a proton.
 
it is approximately equal to the mass of a proton.
Elements are asigned masses in these units which are
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Elements are assigned masses in these units which are
 
not integer numbers. This is because
 
not integer numbers. This is because
 
neutrons and protons have slightly different masses,
 
neutrons and protons have slightly different masses,
 
because nuclear binding forces cause the total mass
 
because nuclear binding forces cause the total mass
of a nucleum to be less than that of the sum of
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of a nucleus to be less than that of the sum of
 
its constituents, and, mainly, because of the
 
its constituents, and, mainly, because of the
 
appearance of natural isotopes. Thus, Potassium
 
appearance of natural isotopes. Thus, Potassium
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isotopes.
 
isotopes.
  
Here is a list of masses of elements and compounds in amus:
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Here is a list of masses of elements and compounds in atomic mass units:
 
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Revision as of 12:33, 25 October 2007

The atomic mass unit (AMU) is defined as the twelfth part of the mass of a C_{12} atom. Its value (in SI units, CODATA value) is

1.66054\times10^{-27} kilograms

Hence, it is approximately equal to the mass of a proton. Elements are assigned masses in these units which are not integer numbers. This is because neutrons and protons have slightly different masses, because nuclear binding forces cause the total mass of a nucleus to be less than that of the sum of its constituents, and, mainly, because of the appearance of natural isotopes. Thus, Potassium has a mass of 39.10 mainly because of natural K^{40} isotopes.

Here is a list of masses of elements and compounds in atomic mass units:

Compound/element mass in amu
Ar 39.95
Xe 131.29
CO2 44.01
H2O (water) 18.02
N2 28.01