Understanding atomic mass units (amu) and weight of particles

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SUMMARY

The carbon-12 (C12) atom is defined to have an atomic mass unit (amu) of exactly 12 amu, despite the calculated mass of its constituent particles being approximately 12.098994 amu. This discrepancy arises from the concept of mass defect, which accounts for the binding energy that holds the nucleus together. The mass defect indicates that the total mass of the nucleus is slightly less than the sum of the individual masses of protons and neutrons due to the energy released during nuclear binding. Understanding this principle is crucial for grasping atomic mass definitions.

PREREQUISITES
  • Understanding of atomic structure, including protons, neutrons, and electrons.
  • Knowledge of atomic mass units (amu) and their significance.
  • Familiarity with the concept of mass defect and binding energy.
  • Basic principles of nuclear physics.
NEXT STEPS
  • Research the concept of mass defect in nuclear physics.
  • Explore the relationship between binding energy and atomic stability.
  • Learn about isotopes and their applications in various fields.
  • Investigate the role of quantum mechanics in atomic mass calculations.
USEFUL FOR

Students of physics, educators teaching atomic theory, and professionals in nuclear science will benefit from this discussion on atomic mass units and the principles governing atomic structure.

solarcopper
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I read that a C12 atom has an atomic mass unit of 12 amu's. A C12 atom has 6 protons, 6 neutrons, and 6 electrons. If the mass of a proton is 1.00728 amu, the mass of a neutron is 1.00867 amu, and the mass of an electron is .000549, how can it's total amu be 12?

6*1.00728+6*1.00867+6*.000549= 12.098994 amu

How did they determine that a C12 atom is 12 amu's? Are they giving an approximate answer?
 
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I found the answer to this question:

"The carbon-12 atom has a mass of 12.000 u, and yet it contains 12 objects (6 protons and 6 neutrons) that each have a mass greater than 1.000 u, not to mention a small contribution from the 6 electrons.

This is true for all nuclei, that the mass of the nucleus is a little less than the mass of the individual neutrons, protons, and electrons. This missing mass is known as the mass defect, and represents the binding energy of the nucleus."

from http://physics.bu.edu/~duffy/sc546_notes10/mass_defect.html
 
Yes, mass defect (or a binding energy) is the answer.
 

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