Hey there! Sign in to join this conversationNew here? Join for free
x Turn on thread page Beta
    • Thread Starter
    Offline

    5
    ReputationRep:
    Hey,

    How is it that the atomic mass of a hydrogen-1 atom is 1.00794 when the atomic mass of a proton is 1,00728. Surely the mass of the constituent nucleons must be greater than the mass of the nucleus, which is taught as fact?

    I do A-Level physics btw, not Chemistry, this is in relation to nuclear fusion and fission, but any explanation of this would be great
    Offline

    8
    ReputationRep:
    I'm no expert, but a hydrogen 1 atom should have an electron in which will increase its mass in comparison to just a proton.
    • Thread Starter
    Offline

    5
    ReputationRep:
    In terms of nuclear physics, it's a well known fact that the total mass of the separated protons and neutrons is always greater than the mass of them in the nucleus. That's how you have binding energy and how energy is released in fission/fusion. And oh sorry I meant to say mass of hydrogen nucleus > mass of proton (i.e. not mass of hydrogen atom, which would also include the mass of the electron).

    So to me this doesn't make much sense Asciant
    Offline

    8
    ReputationRep:
    (Original post by googleit)
    In terms of nuclear physics, it's a well known fact that the total mass of the separated protons and neutrons is always greater than the mass of them in the nucleus. That's how you have binding energy and how energy is released in fission/fusion. And oh sorry I meant to say mass of hydrogen nucleus > mass of proton (i.e. not mass of hydrogen atom, which would also include the mass of the electron).

    So to me this doesn't make much sense Asciant
    Sorry for the late reply, I rarely use TSR tbh.

    Anyhow, using some Wikipedia articles (yh wikipedia I know so shoot me) we can see that the relative atomic mass of hydrogen is 1.00794 u (link), as you stated in your original post. The Ar (relative atomic mass) of an element is the mean of the atomic masses of the isotopes of the element, weighted according to their relative abundance, or its something like that anyway.
    What this means is, basically, this figure is irrelevant for considering binding energies etc. as it is the mean of the 3 different hydrogen isotopes which contain 0/1/2 neutrons.

    If we consider the actual mass of a hydrogen-1 atom we find it to be 1.007825 u (link). You can also see on this page that it claims hydrogen-1 has a binding energy of 0eV to many decimal places, so this should mean that if we add up the relative mass of a proton and an electron we should get 1.007825 u (as a hydrogen-1 atom is simply an electron orbiting a proton).

    Testing this, using these data (proton and electron) we can see:
    1.007276 u + 0.0005485799 u = 1.007825 u

    This is what we were expecting! Yay! Hope that clears anything up.
    Apologies for not doing the maths in (I think) latex, its been a while since I've used it and it is too late figuring how to use it now.
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: May 3, 2016
Poll
Do I go to The Streets tomorrow night?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.