Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: reemie on September 16, 2015, 01:31:28 PM
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The answer according to my booklet is 1.6734×10-24 (g), but I don't understand how we got this answer.
proton: 1.6725×10-24
neutron: 1.6748×10-24
electron: 0.0009×10-24
To get the mass, I added protons with neutrons, but I got 3.3473×10-24.
What am I doing wrong?
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I suppose you're considering the most abundant isotope.
A hydrogen atom doesn't have a neutron. But even if you don't consider the neutron but only the proton you get a different answer. Why?
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I didn't realize that hydrogen doesn't have any neutrons. But if we subtract the number of protons from the answer, we get 9x10-28, and I can't figure out where this number came from.
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You have this number in your list, don't you?
It's the electron!
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Oh, that's right! But why did we add the electrons and the protons to get the mass? Isn't the mass the sum of protons and neutrons? do I have to add all the three particles for every element too to get the mass?
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Isn't the mass the sum of protons and neutrons?
That would yield mass of the nucleus*, not the atom.
*Actually it wouldn't, mass of the nucleus is always lower than the sum of masses of neutrons and protons, with a sole exception of 1H - the lightest hydrogen isotope. Google "mass defect" if you are interested in details.