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### Topic: atomic masses of isotopes  (Read 6183 times)

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#### atakmanga

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##### atomic masses of isotopes
« on: April 26, 2013, 10:18:27 PM »
The atomic masses of nitrogen-14, titanium-48, and xenon-129 are 13.999234 amu, 47.935878 amu, and 128.904779 amu respectfully.

For each isotope, calculate the nuclear mass.  Express your answers using 6 decimal places.

Ok.  Is this the mass defect equation where you take the number of protons times the mass of one proton plus the number of neutrons times the mass of one neutron and subtract it from the given mass?  This is what I did and got .119766, .474122, and 1.202221 respectfully, but my answers are wrong.  I'm not looking for specific answers, only understanding.  I don't know what I'm doing wrong.  I used the values of 1.008 for proton and 1.009 for a neutron.  If anyone could help, I would be very appreciative.

#### Borek

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##### Re: atomic masses of isotopes
« Reply #1 on: April 27, 2013, 02:42:31 AM »
Aren't you going a step too far? Question asks for nuclear masses, not for mass deficits.

And I suppose there are better masses for proton and neutron than the ones you used, I would look for numbers with at least 6 significant digits if that's what you are expected to give in the final answer.
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#### gippgig

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##### Re: atomic masses of isotopes
« Reply #2 on: April 27, 2013, 04:11:13 AM »
The nuclear mass is the atomic mass less the mass of the electrons. Just subtract 7 electron masses for N, 22 for Ti, & 54 for Xe.