why the mass of atom is less than the sum of mass of its atomic particles?
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answers:
Katie J. say: Ever hear of a neutron? Dipshit.
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busterwasmycat say: a small amount of mass is converted to energy. there is potential energy in the particles that is employed in the attachment of the particles into the atom structure (that energy must come from somewhere). It is a very tiny mass, but tiny mass gets important when dealing with 10^23 such items.
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lenpol7 say: By Einsteins theories DeltaE = mc^2
The difference is made up by Enerby (Delta E)
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pisgahchemist say: Mass of the parts of an atom....
Consider the universe in which we live. It's filled with about 90 naturally occurring elements and a large boat-load of chemical combinations of those elements. The elements came into existence early in the history of the universe, after the quarks got their act together forming a soup of protons and neutrons, which, along with electrons, formed hydrogen and helium as well as other particles.
Since we are here to observe the natural complexity, it's safe to say that the universe didn't simply stay a collection of protons and neutrons. Things in nature tend to go spontaneously to lower energy and the protons and neutrons combined to form stable, and more complex, atomic nuclei with the accompanying release of energy.
For instance: 4 protons --> 1 helium nucleus + energy
It is important to understand mass and energy as it relates to Einstein's equation E=mc². A common misconception suggests that matter can be converted into energy or energy converted into matter, but that is not what the equation says. Pick units where c=1. Then E=m. The equation says that mass (not matter) and energy are equivalent.
Now, return to the formation of helium.
4 protons --> 1 helium nucleus + energy
... mass1 ............ mass2 ............ mass3
mass1 = mass2 + mass3
but since mass and energy are equivalent....
mass1 = mass2 + energy
mass3 is the mass defect, which is equivalent to energy, which is called the binding energy.
To summarize:
mass1 is the mass of the individual particles
mass2 is the mass of the combined parts to make the nucleus
... mass2 is less than mass1, and the difference is the mass defect, mass3
mass3 = binding energy .... in accord with E=mc²
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Dixon say: Binding energy
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Dr W say: mass defect
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Roger the Mole say: see https://en.wikipedia.org/wiki/Nuclear_bi... and the rest of the article that contains it.
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