Quote:
|
So if we look at an atom of Nitrogen, the only reason it is not exactly 14 amu is because of the extra electron?
|
Who mentioned electrons?!!!?
The electrons are ALMOST NEVER considered when calculating the atomic mass.
If you read my post you will see that there is something called BINDING ENERGY which subtracts from the sum of the protons and neutrons to give a formula (in the case of nitrogen) 7p + 7n does NOT equal mass of nitrogen.
We take the mass of protons and neutrons as determined by other means (when on their own) and we use a mass spectrometer to measure the mass of the nitrogen atom on its own. The difference between these two values is the mass defect which relates to the binding energy using Einstein's equation E=mc^2
Quote:
Gallium consists of two naturally ocouring isotopes with masses of 68.926 and 70.925 amu. How many protons and neutrons are in the nucleus of each isotope?
Well of course there is 31 protons in each, but how do you know for sure how many neutrons there are? Looking at the answers it would appear that you just round off to the nearest whole number and subtract the protons. This makes sense I guess but why the decimals?
|
you are given the decimals just to demonstrate that the mass values can be measured very accurately indeed. You are correct in assuming that they are not needed for this question.
You could read this as Ga-69 (31p, 38n) and Ga -71 (31p, 40n) without any problems.
Forget about the electrons, they have a mass of approx 0.00054 amu they are not going to affect any calculation at this level.
OK?